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Effects of job-simulated flexibility and strengthflexibility training protocols on maintenance employees engaged in manual handling operations a
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L. GUO , A. GENAIDY , J. WARM , W. KARWOWSKI & J. HIDALGO
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Occupational Biomechanics Laboratory, Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, OH, 45221-0116, USA b
Perception Performance Laboratory, Department of Psychology, University of Cincinnati, Cincinnati, OH, 45221-0376, USA c
Center for Industrial Ergonomics, J. B. Speed Scientific School University of Louisville, Louisville, KY, 40292, USA Published online: 31 May 2007.
To cite this article: L. GUO , A. GENAIDY , J. WARM , W. KARWOWSKI & J. HIDALGO (1992): Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations, Ergonomics, 35:9, 1103-1117 To link to this article: http://dx.doi.org/10.1080/00140139208967385
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Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations L. Guo,' A. GENAIDY,' J. WARM,^ W.KARWOWSKI~ and J . HIDALGO^
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'Occupational Biomechanics Laboratory, Department of Mechanical, Industrial and Nuclear Engineering University of Cincinnati, Cincinnati, OH 4522 1-0 1 1 6, USA 'Perception Performance Laboratory, Department of Psychology University of Cincinnati, Cincinnati, OH 4522 1-0376, USA Tenter for Industrial Ergonomics, J. 8. Speed Scientific School University of Louisville, Louisville, K Y 40292, USA Keywords: Flexibility; Dynamic and static strength; Endurance time; Employees;
Maintenance protocol. This study examined the effects of four flexibility and strength-flexibility training protocols on the dynamic strength, endurance time, and truncal flexibility of 24 maintenance employees engaged in manual material handling operations. The study was conducted over a n 8-week period. Significant improvement in physical capacity was obtained through flexibility training either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase repetition with fixed holding time. The flexibility and strength-flexibility training protocols exhibited similar effects on physical capacity. It was suggested that a follow-up flexibility protocol should be performed on a daily basis in order to maintain the gains obtained in flexibility during the intensivehhort training programme. 1. Introduction Musculoskeletal disorders are rated among the top ten work-related health problems in the United States (CDC 1983a). They are the leading cause of worker disability, and approximately one-half of the members of the US workforce are affected at some time during their working life (Association of Schools of Public Health 1986). Musculoskeietal disorders also account for one-t hird of annual worker compensation. The physical requirements of the manual handling of material have resulted in many of the various musculoskeletal injuries reported in industry (CDC 3 983b). In this regard, lack of physical fitness has been recognized as a possible contributing factor to the etiology of back pain resulting from manual material handting (National Institute for Occupational Safety and Health 1 98 1). Hence, one would expect that physical fitness training could be used as an intervention tool to reduce the frequency and severity of musculoskeletal injuries resulting from manual material handling (M MH) activities in the workplace. There are mixed results reported in the literature about the role of employee fitness programmes in the reduction of injuries, and health care costs in industry (e.g., Hilyer el al. 1990, Cady el al. 1979, Dehlin et al. 1979, Silverstein er al. 1988). The lack of agreement among investigators about the precise role of employee fitness in preventing the frequency and severity of injuries in industry could be attributed to the foIlowing: ( 1 ) training protocols used in some studies did not adhere to the design principles of physical training regimens available in the exercise physiology 0014-0 I W 9 2 $3.00 O 1992 Taylor & Francis Ltd.
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literature; and (2) lack of some knowledge concerning the design of industrial fitness protocols. Examples of important training design principles are:
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( 1 ) the intensity of an initial training protocol should be greater than the work intensity experienced by employees on the job; (2) the technique used in improving a component of a fitness programme such as flexibility should be based on the sound methods used in exercise physiology literature; (3) the tasks undertaken in a training protocol should closely resemble the activities and motions performed by employees on the job in order to gain the maximum benefits from the training protocoi; (4) the physical tests used in evaluating the efficacy of training should simulate the activities undertaken during training. Additional knowledge needed for the design of industrial fitness protocols should concentrate on developing new techniques or modifying existing techniques for maximizing human performance. This is specially important because industrial management is often concerned about use of company time, the number of hours devoted to the programme, the need for special training facilities and equipment, and the simplicity of training methods and instructions so that supervisors and practitioners of occupational safety and health will be able to implement them. Several studies examined the short term effects of physical training for M M H tasks over a period of less than eight weeks (Asfour e! a/. 1984a, Asfour et al. 1 984b, Genaidy et al. 1989, Genaidy el a/. 1990a, Genaidy et a/. 1990b, Genaidy 199 la, 1991b). College students participated in these studies and were inexperienced in MMH. The major conclusions drawn from these studies showed that: ( 1 ) a truncal flexibility protocol significantly improves dynamic muscular strength, low-back flexibility, and truncal rotation; however, the effects of the programme on endurance time were mixed; (2) an endurance training protocol significantly increases endurance time, and may increase both static and dynamic strength only if the weight of load handling dyring the programme taxes the subject to 50% or more of hidher initial dynamic strength; (3) a strength training protocol significantly increases dynamic strength, static strength and endurance lime, with the 10-repetition maximum protocol yielding higher values than the 6-repetition maximum protocol; and (4) for a fixed workload, endurance time increases without changingjob demand perception. Genaidy ct al. ( 1 99 1 ) investigated the effects of strength and strength-flexibility protocols on the physical capacity of employees engaged in industrial MMH tasks. The findings of the study showed that: ( I ) a strength-flexibility training programme can significantly improve endurance time, dynamic and static muscular strength, and truncal flexibility; (2) a dynamic strength training protocol may not improve static strength as much as dynamic strength; (3) a dynamic strength training protocol does not improve low back flexibility; and (4) endurance time increases for a fixed workload without changing job demand perception, and daily operations can be performed more easily. While flexibility is an important component of physical fitness, the effect of flexibility training protocols on employees engaged in M M H was not studied. Since Genaidy ( 199 1b) found that a flexibility training protocol may improve dynamic strength, endurance time, and truncal flexibility of college students, a flexibility protocol should be tested on employees engaged in M M H in
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order to determine its efficacy. If it is successful, it may appeal more to industrial personnel since it does not require any special equipment and is easy to implement. As pointed out by Genaidy ( 1 99 lb), a static stretching may be a practical technique to use in the design of a flexibility protocol. However, it is not known which procedure is better in applying this technique, a progressive increase in exercise repetition with a fixed holding time, a progressive increase in holding time with a fixed exercise repetition, or a progressive increase in both exercise repetition and holding time. 2. Objectives The aforementioned studies did not investigate how to maintain the gains in physical capacity beyond the intensive/short training period (usually eight weeks or less). Research is limited on .how to establish a maintenance exercise programme in industrial settings. Thus further research is warranted to develop a maintenance training protocol for industrial settings. This study was conducted to further understand the effects of job-simulated exercise protocols on the physical capacity of employees engaged in manual materials handling operations. Specifically, the aim of this study was to seek answers to the following questions:
Is it possible to improve the physical capacity (muscular strength, endurance time, and flexibility) of employees engaged in manual handling operations through an intensivekhort flexibility exercise programme? Is it possible to improve the physical capacity through flexibility training as much as a strength-flexibility protocol? Which technique is better to improve flexibility, a progressive increase in the holding time with fixed exercise repetition or a progressive increase in exercise repetition with fixed holding time? Which technique can be used to maintain the gains observed through the shortintensive training?
3. Methods 3.1 . Subjects Twenty-four male maintenance employees from a local hospital volunteered to participate in this study. The employees represented five shops from the maintenance department, i.e., carpenter, electrical, machine, plumbing, and heat, ventilation, and air conditioning. They were engaged in a variety of manual handling tasks during each 8 h work shift. Means and standard deviations of the physical characteristics of the employee population are given in Table 1. No significant differences were found among the various groups in terms of age, body weight, stature, and body weight. Employees were assigned at random to one of four training groups (groups 1,2, 3, and 4). Descriptions of the training groups are given in t he experimental procedures section. During the course of the study, one employee from group 3 and two employees from group 4 did not regularly participate in.the exercise programme due to job emergencies. Thus, their results were not considered in the data analysis. As such, there were six subjects in groups I and 2, five subjects in group 3, and four subjects in group 4. All employees were given instruction about the experimental methods and procedures of the study. This was done by means of an introductory lecture,
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Means and standard deviations (SD) of physical characteristics.
Group
Variable
Mean
SD
Group I Age (years)
Body weight (kg) Stature (cm) Job service (years) Group 2 Age (years) Body weight (kg) Stature (cm) . Job service (years)
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Group 3
A8e (years) Body weight (kg) Stature (cm) Job service (years). Group 4 Age (years) Body weight (kg) Stature (cm) Job service (years)
accompanied by handout materials. All employees signed an informed consent form prior to participation in the study and filled out a general information packet. 3.2. Customizarion of the training programme Prior to the design of the training programmes, supervisors and employees in the various shops were interviewed in order to determine the major activities and critical motions undertaken by employees on a daily basis. Also, employees were observed while performing their daily activities. Following the interviews and observations, the training programme was designed to simulate the activities performed by employees.
3.3. Design and evaluation of intensive/short training The experimental procedures used in this research consisted of two steps: (1) design and evaluation of an intensivelshort training programme; (2) design and evaluation of a follow-up training programme. The details of the intensivehhort training programme are outlined below. Prior to the start of the intensive/short programme, employees were given two educational sessions on physical ergonomics and the effects of physical fitness of the body. The training programme was 4 weeks long at a frequency of 5 times per week (Monday through Friday). The training session duration for each subject was approximately 30 min long, and started each day at the beginning of the shift. Two groups were trained for flexibility (groups 1 and 2). The other groups were trained using strength-flexibility exercises (groups 3 and 4).
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3.3.1. Design of flexibility exercise protocol: Each employee in groups I and 2 performed flexibility exercises for the wrist, forearm, shoulder, trunk, knees, and overall body. The flexibility exercises were performed on a daily basis (see table 2). In a given week, each flexibility exercise was performed at a certain frequency and every employee was instructed to hold the final position for few seconds. The details of the frequency and holding time of flexibility exercises for the four weeks are given in table 3. For group 1, the frequency of exercise was progressively increased while fixing the holding time at 9 s. For group 2, the frequency of exercise was fixed at 7 times and the holding time was progressively increased. Each flexibility exercise group was led by a leader within the group. 3.3.2. Design ofstrength-jlexibilityprotocol: Each employee in groups 3 and 4 started every training session with flexibility exercises, followed by progressive resistance exercise, then flexibility exercises. On Monday, Wednesay, and Friday the progressive resistance exercise was performed for a manual material handling task. On Tuesday and Thursday, the progressive resistance exercise consisted of an upper extremity task. The manual material handling task consisted of the following activities: ( I ) Lift a 38 x 38 x 38 cm box from floor level to elbow level using the straight back-bent knees technique; (2) carry the box horizontally through a distance of 2 13 cm; (3) place the box on a 76 cm-high shelf; (4) push the box horizontally to the maximum reach; (5) pull the box back the same distance as in step 4; (6) lift the box to a 127 cm-high shelf; (7) place the box on the shelf; (8) push the box on the shelf to the maximum reach; (9) pull the box back; (1 0) lift the box to a 178 cm-high shelf; ( I 1) place the box on the shelf; (12) push the box on the shelf to the maximum reach; (1 3) pull the box back; (1 4) lower the box to elbow level; (1 5) hold the box and turn around 180"; (6) carry the box through a distance of 2 13 cm; (1 7) lower the box on the floor using the straight back-bent knees technique. The elements of upper extremity exercise were: ( I ) the subject started the exercise by standing in an erect position with the forearm perpendicular to his trunk and the upper arms vertical (parallel and adjacent to the trunk); (2) flex and extend the right wrist with a load in the hand while maintaining the initial position; (3) pronate and supinate the right forearm around the elbow; (4) flex and extend the right forearm around the elbow; (5) flex and extend the right upper extremity around the shoulder; (6) flex and extend the left wrist with a load in the hand; (7) pronate and supinate the left forearm around the elbow; (8) flex and extend the left forearm around the elbow; (9) flex and extend the left upper extremity around the shoulder. When the subject flexes, extends pronates or supinates, the ending point of the trajectory of motion is held for 5 s (by counting from 1 to 5). Exercises for the shoulder flexionlextension, sit and reach, lateral bending, trunk rotation, lumbar spine flexionlextension, and straight back-bent knees flexibility exercises were performed on Monday, Wednesday, and Friday of each week. The shoulder flexionlextension, forearm rotation, and wrist flexionlextension flexibility exercises were practiced on Tuesday and Thursday of every week. The details of the frequency and holding time of flexibility exercises for the four weeks are given in table 3. The progressive increase in frequency of exercise repetition for group 3 was similar to that of group 1. Also, the progressive increase in holding time for group 4 was the same as that of group 2. This was necessary to allow comparison between the flexibility and strength-flexibility protocols. In this study, the ten repetition maximum (1 0 RM) technique of progressive
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Table 2. Description of flexibility exercises. Flexibility exercise Lumbar spine
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Lateral bending
Trunk rotation
Sit and reach
Wrist flexion1 extension
Forearm rotation
Shoulder flexion/ extension
Knee flexion/ extension Overall body
Description The subject starts the exercise from an flexion/extension erect position Bends the trunk forward around waist height with the hands reaching for the toes (lumbar spine flexion) and straight knees Moves the trunk to an erect position Places the hands around the waist Bends the trunk backward as far as possible (lumbar spine extension) The subject returns to initial posture The subject begins from an erect position Places the hands around the waist Bends the trunk laterally to one side with straight knees Moves the trunk to an erect posture Bends it laterally to the other side The subject resumes the initial posture The subject begins from an erect position Places the hands around the waist Rotates the trunk laterally to one side with straight knees Moves the trunk to an erect posture Rotates it laterally to the other side The subject resumes the initial posture At the beginning of the exercise, the subject lies down on the floor Moves the trunk up then forward with the hands reaching for the toes The subject resumes the initial position The subject stans the exercise from an erect position with the foreanns perpendicular to the trunk and the upper arms vertical (parallel and adjacent to the trunk) Flexes the wrist Extends the wrist The subject resumes the initial position The subject stans the exercise from an erect position with the forearms perpendicular to the trunk and the upper arms vertical (parallel and adjacent to the trunk) Pronates the forearm around the elbow Supinates the forearm around the elbow The subject resumes the initial position The subject starts the exercise from an erect position with the upper extremity venical (parallel and adjacent to the trunk) Hexes the upper extremities around the shoulder Extends the upper extremities around the shoulder The subject resumes the initial position the subject starts the exercise from an erect position The subject bends the knees with straight back and hands around the waist The subject resumes the initial position The subject starts the exercise by standing on knees with straight back, lower legs parallel to the thighs, and angle flexed on the floor Flexes the trunk forward until the forehead gets close to the floor In the position taken in step 2, the hands touch the floor (bent around the wrist) The subject resumes the initial position
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Table 3. Frequency and holding time of flexibility exercises for various training groups
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Group No.
Frequency of flexibility exercise week I week 2 week 3 week4
week 1
Holding lime week 3
week 2
week 4
resistance exercise was used (Genaidy et al. 1990). The 10 RM load was defined as the maximum load that an employee could handle ten consecutive times without resting between the repetitions for the task under consideration. The ten-repetition maximum technique required the subject to perform a total of 30 repetitions per training session divided into three sets of ten repetitions each as folIows: (1) set 1= 10 repetitions at a load of 112 the.10 RM load; (2) set 2= 10 repetitions at a load of 314 the 10 RM load; (3) set 3-1 10 repetitions at a load equal to the 10 RM load. The subject was asked to continue training at the 10 RM load until he was able to perform twelve repetitions of set 3, then the I0 RM load was increased by 4 kg for the overall body manual material handling task and 2 kg for the upper extremity manual handling task and was considered as the new 10 RM load for the next training session. Two minutes of rest was provided between two consecutive sets.
3.3.3. Evaluation of training protocols: Each employee was tested twice, separated by a period of four weeks. The various tests included dynamic and static strength, muscular endurance, and flexibility. The tests were conducted in the week prior to the start and the week after the end of the intensivelshort training programme. The muscular endurance test required each employee t o perform the overall body manual material task described in the previous section until he/she could not perform it any longer due to local muscular fatigue andlor overall body fatigue. The test duration was defined as endurance time, and was recorded upon termination of the exercise. Each subject handed a load equal to 75% of the subject's initial dynamic strength and contained in a 38 cm x 38 cm x 25 cm box. Dynamic strength was defined as the maximum amount of load contained in a 38 cm x 38 cm x 25 ern box that could be handled for the overall body manual material handling task through a single trial. For each static measurement, the subject was attached to a handle connected to a load cell which is hooked to an electronic device with a digital readout to measure the exerted force. Static strength measured were recorded according to the procedures reported by Ayoub et al. (1977). The flexibility measurements consisted of: (1) sit and reach, (2) truncal rotation; (3) lateral bending; and (4) lumbar spine extension. Each test was repeated three times, with thirty seconds of rest between trials for the same test and 2 min of rest between two consecutive tests. The final score for each test was the average of the three trials. Before any starting any test, a warm-up of five stretches was performed by each subject. The sit and reach test followed the guidelines of Wilmore (1 986). Lateral bending was examined by recording the difference between the position of the fingertips in erect standing and in maximal side bending to the right and left sides (Battie et a/.
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1987). The subject was instructed to keep the knees straight and both heel on the floor when bending to the side. The lumbar spine extension was measured in a standing position using a goniometer which was placed on the first lumbar vertebra. In the truncal rotation test, leftlright truncal rotation was measured by attaching a belt around the subject's chest. A pointer was connected to the belt so that it recorded the angular rotation of the spine. 3.4. Design and evaluation offollow-up programme The objective of follow-up training was to sustain the improved performance that may be gained from the shortlintensive training programme. A flexibility exercise programme was implemented at the beginning of the shift twice a week. The duration of the follow-up programme was four weeks. The programme consisted of the exercises described in table 2. For groups 1 and 3, each exercise was repeated 12 times with a count of 9 at the final position. For groups 2 and 4, each exercise was performed 7 times with a count of 14 at the final position. The evaluation of the follow-up programme was performed in the week following the completion of the follow-up protocol. The same dependent variables collected during the intensive/short training programme were also measured at this time. For each group, measurements collected prior to the start of the follow-up programme were compared to those obtained at the end of the programme.
3.5. Data analysis Several approaches can be used for the statistical analysis of the data obtained in the present investigation. Huck and McLean (1975) recommended that, for a pretest-post-test design, analysis of covariance should be used to assess the degree to which the four study groups differed in response measures at the end of the intensivelshort training or follow-up training protocol. The post-test response measure served as the dependent variable while the pre-test value served as the covariate. Analysis of covariance was conducted for each response measure. An analysis of variance was conducted for each experimental group in order to determine whether there was a significant change from pre-treatment to posttreatment for each rcsponse variable (Asfour et al. 1990). The analysis of covariance and variance were conducted using the General Linear Model Procedure 'GLM'of the Statistical Analysis System Software (SAS 1 985). 4.
Results
4 . 1 . Descriptive sfatistics
Means and standard deviations of response measures for the intensivelshort training programme are given in table 4. Post-test flexibility measures, dynamic strength, and endurance time increased with respect to the pre-test measures among all training groups. The average gains in flexibility measures due to training for groups 1, 2, 3, and 4 were 26%, 29%, 26%, and 20%, respectively. A minimum improvement of 99% was achieved in terms of endurance time. The average percentage increase in dynamic strength ranged from 28% to 59%. Post-test static strength measures were higher than the pre-test measures for the second flexibility group and the strengthflexibility groups. Less gains were obtained for the first flexibility group. The average percent increase in static strength was 6%, 17%, 25%, and 30%, respectively, for groups 1, 2, 3, and 4.
Flexibility and dynamic strength Table 4.
Descriptive statistics of response measures for in tensivehhort training programme.
Group response measure
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I
1111
Pre-test SD mean
Post-test mean SD
Percentage change
Group 1 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) cm Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 2 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 3 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach Lateral bending (right) Lateral bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 4 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (crn) Lateral bending (right) (deg.) Lateral bending (left) (deg.) Rotat ion (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Note: Group I-first flexibility group; Group 2-second flexibility group; Group 3-first strength-flexibili ty group; Group 4-second strength-flexibili ty group.
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The means and standard deviations of the response measures for the follow-up training programme are given in table 5. There was a loss in flexibility for both flexibility protocols. The average loss was 1 1 % and 7016, respectively for b o ~ h protocols. Static strength was not affected. The average percentage change was 2.3% and 0.4% for both flexibility protocols, respectively. Sim-ilar results were obtained in terms of dynamic strength and dynamic endurance. However, dynamic endurance increased 24% for the second flexibility protocol. Table 5. Descriptive statistics of response measures for follow-up training programme. Pre-test mean SD
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Group response measure
Post-test SD mean
Percentage change
Group I Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) tateral bending (right) Literal bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 2 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) Lateral bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Note: Group I -first
flexibility group; Group 2-second
flexibility group.
4.2. Analysis of variance and covariance The results of analysis of covariance for the intensive/short training protocol are summarized in table 6, and indicate that: (1) there were no significant differences between the flexibility group; (2) there were no significant differences between the strength-flexibility groups, except endurance time where the second strength-flexibility protocol yielded higher gains; (3) the first strength-flexibility group resulted only in significantly higher static arm and dynamic strength values than the first flexibility group, and endurance time was higher for the second strength-flexibility group than the second flexibility group. No other differences were found between the two groups. The analysis of variance results showed that dynamic strength and endurance time
Flexibility and dynamic strength were statistically significant for all training groups (tabje 7). In the post-test, most flexibility measures were significantly higher than those in pre-tests. Static strength was significantly improved for all groups, except the first flexibility group which did not experience any significant change. Table 6. Analysis of covariance results for various groups in intensivelshort training programme.
Response measure
Significance level G3 G1 G2 vs vs vs vs G2 G 4 G3 G 4
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateralbending(right)(cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg) Lumbar spine extension (deg.)
NS NS NS NS S NS NS NS NS NS NS NS
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Gf
GI
NS NS NS
NS NS NS NS NS NS NS
NS
NS
NS
82
NS
NS
NS
37
NS
NS
Groups G2 G3
429 477 533 586 622 619 1036 1097 1153 1382 1394 1580 424 505 527 10-3 10 11.4 25 26 28 22 27 27
S NS NS NS S NS NS NS NS NS
NS NS NS NS NS S
NS NS
.
26 84
G4 549
609 1123
1720 475
26
23
16 27 24 23
84 91 36
84 85
84 82
37
37
Note: Adjusted means of response variables are reported.
Table 7. Analysis of variance results for intensivelshort training programme. Response measure
GI
Groups G2 G3
G4
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Nole: G !-Group i ; G2-Group 2: G3-Group 3; G4-Group 4; S-statistically cant at the 5% level; NS-statistically non-significant at the 5% level.
signifi-
For the follow-up protocols, the analysis of covariance indicated no significant differences between the two training groups in terms of static and dynamic strength, and all flexibility measures (table 8). Endurance time was significantly higher for the second flexibility group. No significant differences were found between the pre-test
.
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and post-test measures of static and dynamic strength for both flexibility protocols (table 9). O n the other hand, significant differences were obtained in terms of flexibility measures for both flexibility protocols. Table 8. Analysis of covariance results for follow-up training programme.
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Response measure
Significance level
Adjusted means G1 G2
Static arm strength (N) Static shoulder strength Static back strength (N) Static composite strengt Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (leh) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Nore: Adjusted means of response variables are reported.
Table 9. Analysis of variance results for follow-up training programme. Groups Response measure
G1
G2
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
5. Discussion Most physical training studies on manual material handling tasks were conducted on college students. This study utilized as subjects hospital management workers who were engaged in various types of manual handling tasks over an eight-week period. In the first four weeks,.employees were divided into four groups and each group was given a different training protocoi. All protocols were designed to permit comparison among the four training groups. In the following four weeks of the study, employees were split into two groups.
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5.1. Inrensive/short programme ' Both flexibility training groups resulted in significant improvement in dynamic strength, endurance time, and flexibility measures during the course of intensive1 short training. Static strength was only improved for the second flexibility group. Overall, no significant differences were found between the two protocols except for the dynamic strength. In general, it seems that by progressively increasing the number of exercise repetitions or holding time, similar improvement in physical capacity could be obtained. The results obtained from the flexibility groups are comparable to those obtained in Genaidy (1 99 1 b) for college students. Genaidy ( 1 99 1b) reported a 20.2Oh increase in truncal rotation, 2 1.4% improvement in low back flexibility, and 36.5% change in dynamic strength for male college students following a 4-week training programme. In this study, there was 28.4%, 28-3%, and 39% improvement in truncal rotation, low-back flexibility (sit and reach) and dynamic strength, respectively, for the flexibility groups. Each strength-flexibility training protocol resulted in significant improvement in employees' physical capacity. Moreover, no significant differences were obtained between the two groups for each dependent variable, except for dynamic endurance where the second protocol resulted in higher values. Thus, such strength-flexibility protocol was equally effective in improving physical capacity. The strength-flexibility protocol used in Genaidy et al. ( 1 991) scored high gains in dynamic strength (85.8%), endurance time ( I 24-2%), and low back flexibility (48-4%), comparable to those obtained in this study for the strength-flexibility groups (improvements in dynamic strength-52.4%; endurance time- 1 50.2%; and low back flexibility-27.2%). There was no major differences between the strength-flexibility and flexibility groups in terms of physical capacity. This could be interpreted in two different ways. A flexibility protocol may be as effective as the strength-flexibility protocol in improving physical capacity. On the other hand, the 4-week duration of training may be too short to detect any substantial differences since the strengt h-flexibility protocols generally resulted in greater performance improvement than the flexibility protocols. Finally, employees reported that, after the first week of training, they started to feel the positive effects of exercise during leisure time. They reported engaging in many activities without being fatigued. Thus, it seems that exercise may have both physical and psychological effects on employees. In this study, the physical effects were only recorded. Therefore, future studies should test if exercise has any psychological effects. Sime ( 1 984) pointed out that those who exercise regularly have reported reduced anxiety and depression, improved mood and self-esteem, and a better sense of self-control.
5.2. Follow-up programme Both static and dynamic strengths remained almost unchanged during the course of the follow-up programme. On the other hand, there was a loss in flexibility measures. Significant losses were found for some flexibility measures, with more pronounced losses for the flexibility protocol. These results indicate that a follow-up flexibility exercise protocol performed at a rate of 2 timeslweek is not adequate to maintain the gains obtained from the intensivelshort training programme. Thus, it is suggested that a follow-up flexibility training protocol should be performed on a daily basis.
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5.3. General observations The flexibility and strength-flexibility training protocols produced comparable effects on the physical capacity of employees within the 4-week period investigated in this research. It seems that this period should be extended in order to determine the desired role of each protocol in improving human capability. There are different views regarding improving human capability through flexibility and strength training protocols. Hartley-O'Brien ( 1 980) suggested that flexibility may be increased by either decreasing the resistance of target muscle or increasing the strength of opposing muscles. Physiologically, resistance to stretch may be decreased in two ways: (1) by actual physical lengthening of the connective tissues; and (2) by relaxation of the muscle under stretch. Increasing the strength of the muscles that will activate the range of motion can be achieved by various muscle loading activities as well as by reflexive facilitatory techniques. Chapman er a/. (1 972) reported that progressive, resistance exercise improved the strength and joint mobility of the index fingers. Massey and Chaudet ( 1 955) pointed out that progressive resistance may increase the range of motion in joints exercised, while it may actually restrict movements in areas that are not exercised. They attributed this phenomenon to an imbalance in development of the muscles surrounding or affecting the movement of a joint. 6. Conclusions The results of this study showed that significant improvements in physical capacity could be achieved through a flexibility training programme. Improvement in physical capacity can be assured either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase in exercise repetition with fixed holding time. The progressive increase in holding time yielded slightly higher values. No significant differences were found between the flexibility and strengthflexibility training protocols in terms of physical capacity. However, the strengthflexibility protocols resulted, on the average, in higher percent improvement in physical capacity. A follow-up performed at a rate of 2 timedweek is not adequate to maintain the performance levels gained from the initial training, thus, it is suggested that a follow-up flexibility protocol should be performed on a daily basis to sustain these gains. Finally, no major differences were obtained among the two flexibility protocols during the follow-up programme. However, the progressive increase in holding'time resulted in less losses in terms of flexibility. References ASFOUR, S. S., AYOUB,M . M. and M r r a , A. l984a, EfTects on an endurance and strength
training programme on lifting capacity of males, Ergonomics, 27, 435-442. ASFOUR,S. S., DUTTA,S. P. and TABOUN, S. M. 1984b, The effects of training on static strength and carrying capacity of college males, in: A. Mital, Trends in Ergonomics/Human Factors I (Elsevier Science Publishers, Amsterdam), 1 6 1-1 66. ASFOUR,S. S., KHALIL,T.M., WALY, S. M., GOLDBERG, M. L., ROSOMOFF, R. S. and Roso~om,H. L. 1990, Biofeedback in back muscle strengthening, Spine, 15, 510-513. ASSOCIATION OF SCHOOLSOF PUBUCH ULTH 1 9 86, Propos~dNational Strategiesfor !he Prevmtion of Leading Work-related Diseases and Injuries, Pad I , prepared for National Insti tute for Occupational Safety and Health (Cincinnati, OH), Pb87- 1 14740; reprinted by US Depanment of Commerce, National Technical Information Service. AYOUB,M. M., DEIVANAYAGAM, S. and BAKKEN,G . 1977, A preliminary manual for selected an thropometric strength and endurance measurement. Texas Tech University Report, Texas Tech University, Lubbock, TX.
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h m ~ M. , C., BIGOS, S. J., SHEELY, A. and WORTLEY, M. D. 1987, Spinal flexibility and individual factors that influence it, Physical Therapy, 67, 653-658. CADY,L. D., B r m o m , D. P., O'CONNELL,E. R., THOMAS, P. C. and A w , J. H. 1979, Strength and fitness and subsequent back injuries in fire fighters, Journal of Occuparional Medicine, 21, 269-272. E. A., DE VRIES,H. A. and SWEZEY, K. 1972, Joint stiffness: effects of exercise on CHAPMAN, young and old men, Journal of Gerontology, 77, 2 1 8-22 1 . C ~ R FOR S DISEASECOKIROL1983a, Leading work-related diseases and injuries-Uni ted States, Morbidity and Mortality Weekly Reporr, 32 (2), 24-26, 32. CENTERS FOR DISEASE COKIROL198 3b, Musculoskeletal injuries, Morbidity and Mortality Weekl-v Reporr, 32( 14), 1 89- 1 9 1. DEHUN, O., BERG,S., ANDERSSON, G. B. J. and GRIMBY, G. 198 1, Effect of physical training and ergonomic counselling on the psychological perception of work and on the subjective assessment of Iow-back insufficiency, Scandinavian Journal ofRehabilitation Medicine, 13, 1-9. GENAIDY, A. M. 199 la, A physical training programme for manual handling operations, Ergonomics, 34, 1 - 1 1 . GENMDY,A. M. 1 99 1b, Truncal flexibility exercise effects on musculoskeletal capability for manual handling tasks, Applied Ergonomics, 22, 1 55- 1 62. GENMDY, A. M., BAMA,K. M., SARMIDY, R. and SXNA,P. 1 WOa, An endurance training program for symmetrical and asymmetrical manual lifting tasks, Journal oJOccupationa1 Medicine, 32, 226-2 33. GENAIDY, A. M., DAVIS,N., D E L G E., ~ ,GARCIA,S. and AL-HERUIU, E. 1992, Musculoskeletal exercise effects on employees performing manual handling operations in manufacturing industry, Ergonomics, in press. GENAIDY. A. M., GUPTA,T., and ALSHEDI, A. 1990b, Improving human capabilities for combined manual materials handling through a short and intensive physical training program, American lndusrrial Hygiene Association Journal, 51, 810-814. GENMDY,A. M., MITAL, A., and BAFNA,K. 1989, A n endurance training programme for frequent manual carrying tasks, Ergonomics, 32, 149-155. S. .I. 1980, Six mobilization exercises for active range of hip flexion, HARTLEY-O'BRIW, Research Quarterly for Exerci-ye and Sport, 51, 625-63 5. HILYER, J. C., BROWN,K. C., SIRES,A. T.,and PEOPLES,L. 1990, A flexibility intervention to reduce the incidence and severity of joint injuries among municipal firefighters, Journal of Occupational Medicine, 32, 63 1-637. HUCK, S. W. and MCLEAN, R. A. 1975, Using a repeated measures ANOVA to analyse the data from a pre-test-post-test design: a potentially confusing task, Psychological Bulletin, 82, 5 1 1-518. MASSEY, B. H. and CHANDET, N. L. 1956, Effects of systematic, heavy resistive exercise on range of joint movement in young male adults, Research Quarterly, 27, 4 1-5 1. NATIONAL INSTITUTE FOR OCCUPATIONAL S m AND HEALTH 1 98 1, Work Prac!ices Guide for Manual Lifring. DHHS (NOSH), Publication No. 8 1-1 22, March. SILVERSTEM, B. A., A R M ~ R O NT.GJ., , LONGMATE,A. and WOODY,D. 1 98 8, Can in-plant exercise control musculoskeletal symptoms? Journal of Occupational h4edicine, 30, 922-92 7. SIME,W. E. 1 984, Psychological benefits of exercise training in the healthy individual, in J. D. Matarazzo (ed.) Behavioral Healrh: A Handbook of Health Enhancement and Disease Prevenrion (John Wiley and Sons, New York), 488-508. S T A T I ~ UANALYSIS L SYSTEM1 985, SAS User's Guide: Statistics, Version 5 (SAS Institute Inc., Cary, NC). WILMORE, J. H. 1 986, Sensible Fitness, Second Edition (Leisure Press, Champaign, Ill). Rcccivcd 20 September 1 99 1. Revision accepted 10 December 1991.
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Effects of job-simulated flexibility and strengthflexibility training protocols on maintenance employees engaged in manual handling operations a
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b
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L. GUO , A. GENAIDY , J. WARM , W. KARWOWSKI & J. HIDALGO
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Occupational Biomechanics Laboratory, Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, OH, 45221-0116, USA b
Perception Performance Laboratory, Department of Psychology, University of Cincinnati, Cincinnati, OH, 45221-0376, USA c
Center for Industrial Ergonomics, J. B. Speed Scientific School University of Louisville, Louisville, KY, 40292, USA Published online: 31 May 2007.
To cite this article: L. GUO , A. GENAIDY , J. WARM , W. KARWOWSKI & J. HIDALGO (1992): Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations, Ergonomics, 35:9, 1103-1117 To link to this article: http://dx.doi.org/10.1080/00140139208967385
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Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations L. Guo,' A. GENAIDY,' J. WARM,^ W.KARWOWSKI~ and J . HIDALGO^
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'Occupational Biomechanics Laboratory, Department of Mechanical, Industrial and Nuclear Engineering University of Cincinnati, Cincinnati, OH 4522 1-0 1 1 6, USA 'Perception Performance Laboratory, Department of Psychology University of Cincinnati, Cincinnati, OH 4522 1-0376, USA Tenter for Industrial Ergonomics, J. 8. Speed Scientific School University of Louisville, Louisville, K Y 40292, USA Keywords: Flexibility; Dynamic and static strength; Endurance time; Employees;
Maintenance protocol. This study examined the effects of four flexibility and strength-flexibility training protocols on the dynamic strength, endurance time, and truncal flexibility of 24 maintenance employees engaged in manual material handling operations. The study was conducted over a n 8-week period. Significant improvement in physical capacity was obtained through flexibility training either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase repetition with fixed holding time. The flexibility and strength-flexibility training protocols exhibited similar effects on physical capacity. It was suggested that a follow-up flexibility protocol should be performed on a daily basis in order to maintain the gains obtained in flexibility during the intensivehhort training programme. 1. Introduction Musculoskeletal disorders are rated among the top ten work-related health problems in the United States (CDC 1983a). They are the leading cause of worker disability, and approximately one-half of the members of the US workforce are affected at some time during their working life (Association of Schools of Public Health 1986). Musculoskeietal disorders also account for one-t hird of annual worker compensation. The physical requirements of the manual handling of material have resulted in many of the various musculoskeletal injuries reported in industry (CDC 3 983b). In this regard, lack of physical fitness has been recognized as a possible contributing factor to the etiology of back pain resulting from manual material handting (National Institute for Occupational Safety and Health 1 98 1). Hence, one would expect that physical fitness training could be used as an intervention tool to reduce the frequency and severity of musculoskeletal injuries resulting from manual material handling (M MH) activities in the workplace. There are mixed results reported in the literature about the role of employee fitness programmes in the reduction of injuries, and health care costs in industry (e.g., Hilyer el al. 1990, Cady el al. 1979, Dehlin et al. 1979, Silverstein er al. 1988). The lack of agreement among investigators about the precise role of employee fitness in preventing the frequency and severity of injuries in industry could be attributed to the foIlowing: ( 1 ) training protocols used in some studies did not adhere to the design principles of physical training regimens available in the exercise physiology 0014-0 I W 9 2 $3.00 O 1992 Taylor & Francis Ltd.
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literature; and (2) lack of some knowledge concerning the design of industrial fitness protocols. Examples of important training design principles are:
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( 1 ) the intensity of an initial training protocol should be greater than the work intensity experienced by employees on the job; (2) the technique used in improving a component of a fitness programme such as flexibility should be based on the sound methods used in exercise physiology literature; (3) the tasks undertaken in a training protocol should closely resemble the activities and motions performed by employees on the job in order to gain the maximum benefits from the training protocoi; (4) the physical tests used in evaluating the efficacy of training should simulate the activities undertaken during training. Additional knowledge needed for the design of industrial fitness protocols should concentrate on developing new techniques or modifying existing techniques for maximizing human performance. This is specially important because industrial management is often concerned about use of company time, the number of hours devoted to the programme, the need for special training facilities and equipment, and the simplicity of training methods and instructions so that supervisors and practitioners of occupational safety and health will be able to implement them. Several studies examined the short term effects of physical training for M M H tasks over a period of less than eight weeks (Asfour e! a/. 1984a, Asfour et al. 1 984b, Genaidy et al. 1989, Genaidy el a/. 1990a, Genaidy et a/. 1990b, Genaidy 199 la, 1991b). College students participated in these studies and were inexperienced in MMH. The major conclusions drawn from these studies showed that: ( 1 ) a truncal flexibility protocol significantly improves dynamic muscular strength, low-back flexibility, and truncal rotation; however, the effects of the programme on endurance time were mixed; (2) an endurance training protocol significantly increases endurance time, and may increase both static and dynamic strength only if the weight of load handling dyring the programme taxes the subject to 50% or more of hidher initial dynamic strength; (3) a strength training protocol significantly increases dynamic strength, static strength and endurance lime, with the 10-repetition maximum protocol yielding higher values than the 6-repetition maximum protocol; and (4) for a fixed workload, endurance time increases without changingjob demand perception. Genaidy ct al. ( 1 99 1 ) investigated the effects of strength and strength-flexibility protocols on the physical capacity of employees engaged in industrial MMH tasks. The findings of the study showed that: ( I ) a strength-flexibility training programme can significantly improve endurance time, dynamic and static muscular strength, and truncal flexibility; (2) a dynamic strength training protocol may not improve static strength as much as dynamic strength; (3) a dynamic strength training protocol does not improve low back flexibility; and (4) endurance time increases for a fixed workload without changing job demand perception, and daily operations can be performed more easily. While flexibility is an important component of physical fitness, the effect of flexibility training protocols on employees engaged in M M H was not studied. Since Genaidy ( 199 1b) found that a flexibility training protocol may improve dynamic strength, endurance time, and truncal flexibility of college students, a flexibility protocol should be tested on employees engaged in M M H in
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order to determine its efficacy. If it is successful, it may appeal more to industrial personnel since it does not require any special equipment and is easy to implement. As pointed out by Genaidy ( 1 99 lb), a static stretching may be a practical technique to use in the design of a flexibility protocol. However, it is not known which procedure is better in applying this technique, a progressive increase in exercise repetition with a fixed holding time, a progressive increase in holding time with a fixed exercise repetition, or a progressive increase in both exercise repetition and holding time. 2. Objectives The aforementioned studies did not investigate how to maintain the gains in physical capacity beyond the intensive/short training period (usually eight weeks or less). Research is limited on .how to establish a maintenance exercise programme in industrial settings. Thus further research is warranted to develop a maintenance training protocol for industrial settings. This study was conducted to further understand the effects of job-simulated exercise protocols on the physical capacity of employees engaged in manual materials handling operations. Specifically, the aim of this study was to seek answers to the following questions:
Is it possible to improve the physical capacity (muscular strength, endurance time, and flexibility) of employees engaged in manual handling operations through an intensivekhort flexibility exercise programme? Is it possible to improve the physical capacity through flexibility training as much as a strength-flexibility protocol? Which technique is better to improve flexibility, a progressive increase in the holding time with fixed exercise repetition or a progressive increase in exercise repetition with fixed holding time? Which technique can be used to maintain the gains observed through the shortintensive training?
3. Methods 3.1 . Subjects Twenty-four male maintenance employees from a local hospital volunteered to participate in this study. The employees represented five shops from the maintenance department, i.e., carpenter, electrical, machine, plumbing, and heat, ventilation, and air conditioning. They were engaged in a variety of manual handling tasks during each 8 h work shift. Means and standard deviations of the physical characteristics of the employee population are given in Table 1. No significant differences were found among the various groups in terms of age, body weight, stature, and body weight. Employees were assigned at random to one of four training groups (groups 1,2, 3, and 4). Descriptions of the training groups are given in t he experimental procedures section. During the course of the study, one employee from group 3 and two employees from group 4 did not regularly participate in.the exercise programme due to job emergencies. Thus, their results were not considered in the data analysis. As such, there were six subjects in groups I and 2, five subjects in group 3, and four subjects in group 4. All employees were given instruction about the experimental methods and procedures of the study. This was done by means of an introductory lecture,
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Means and standard deviations (SD) of physical characteristics.
Group
Variable
Mean
SD
Group I Age (years)
Body weight (kg) Stature (cm) Job service (years) Group 2 Age (years) Body weight (kg) Stature (cm) . Job service (years)
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Group 3
A8e (years) Body weight (kg) Stature (cm) Job service (years). Group 4 Age (years) Body weight (kg) Stature (cm) Job service (years)
accompanied by handout materials. All employees signed an informed consent form prior to participation in the study and filled out a general information packet. 3.2. Customizarion of the training programme Prior to the design of the training programmes, supervisors and employees in the various shops were interviewed in order to determine the major activities and critical motions undertaken by employees on a daily basis. Also, employees were observed while performing their daily activities. Following the interviews and observations, the training programme was designed to simulate the activities performed by employees.
3.3. Design and evaluation of intensive/short training The experimental procedures used in this research consisted of two steps: (1) design and evaluation of an intensivelshort training programme; (2) design and evaluation of a follow-up training programme. The details of the intensivehhort training programme are outlined below. Prior to the start of the intensive/short programme, employees were given two educational sessions on physical ergonomics and the effects of physical fitness of the body. The training programme was 4 weeks long at a frequency of 5 times per week (Monday through Friday). The training session duration for each subject was approximately 30 min long, and started each day at the beginning of the shift. Two groups were trained for flexibility (groups 1 and 2). The other groups were trained using strength-flexibility exercises (groups 3 and 4).
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3.3.1. Design of flexibility exercise protocol: Each employee in groups I and 2 performed flexibility exercises for the wrist, forearm, shoulder, trunk, knees, and overall body. The flexibility exercises were performed on a daily basis (see table 2). In a given week, each flexibility exercise was performed at a certain frequency and every employee was instructed to hold the final position for few seconds. The details of the frequency and holding time of flexibility exercises for the four weeks are given in table 3. For group 1, the frequency of exercise was progressively increased while fixing the holding time at 9 s. For group 2, the frequency of exercise was fixed at 7 times and the holding time was progressively increased. Each flexibility exercise group was led by a leader within the group. 3.3.2. Design ofstrength-jlexibilityprotocol: Each employee in groups 3 and 4 started every training session with flexibility exercises, followed by progressive resistance exercise, then flexibility exercises. On Monday, Wednesay, and Friday the progressive resistance exercise was performed for a manual material handling task. On Tuesday and Thursday, the progressive resistance exercise consisted of an upper extremity task. The manual material handling task consisted of the following activities: ( I ) Lift a 38 x 38 x 38 cm box from floor level to elbow level using the straight back-bent knees technique; (2) carry the box horizontally through a distance of 2 13 cm; (3) place the box on a 76 cm-high shelf; (4) push the box horizontally to the maximum reach; (5) pull the box back the same distance as in step 4; (6) lift the box to a 127 cm-high shelf; (7) place the box on the shelf; (8) push the box on the shelf to the maximum reach; (9) pull the box back; (1 0) lift the box to a 178 cm-high shelf; ( I 1) place the box on the shelf; (12) push the box on the shelf to the maximum reach; (1 3) pull the box back; (1 4) lower the box to elbow level; (1 5) hold the box and turn around 180"; (6) carry the box through a distance of 2 13 cm; (1 7) lower the box on the floor using the straight back-bent knees technique. The elements of upper extremity exercise were: ( I ) the subject started the exercise by standing in an erect position with the forearm perpendicular to his trunk and the upper arms vertical (parallel and adjacent to the trunk); (2) flex and extend the right wrist with a load in the hand while maintaining the initial position; (3) pronate and supinate the right forearm around the elbow; (4) flex and extend the right forearm around the elbow; (5) flex and extend the right upper extremity around the shoulder; (6) flex and extend the left wrist with a load in the hand; (7) pronate and supinate the left forearm around the elbow; (8) flex and extend the left forearm around the elbow; (9) flex and extend the left upper extremity around the shoulder. When the subject flexes, extends pronates or supinates, the ending point of the trajectory of motion is held for 5 s (by counting from 1 to 5). Exercises for the shoulder flexionlextension, sit and reach, lateral bending, trunk rotation, lumbar spine flexionlextension, and straight back-bent knees flexibility exercises were performed on Monday, Wednesday, and Friday of each week. The shoulder flexionlextension, forearm rotation, and wrist flexionlextension flexibility exercises were practiced on Tuesday and Thursday of every week. The details of the frequency and holding time of flexibility exercises for the four weeks are given in table 3. The progressive increase in frequency of exercise repetition for group 3 was similar to that of group 1. Also, the progressive increase in holding time for group 4 was the same as that of group 2. This was necessary to allow comparison between the flexibility and strength-flexibility protocols. In this study, the ten repetition maximum (1 0 RM) technique of progressive
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Table 2. Description of flexibility exercises. Flexibility exercise Lumbar spine
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Lateral bending
Trunk rotation
Sit and reach
Wrist flexion1 extension
Forearm rotation
Shoulder flexion/ extension
Knee flexion/ extension Overall body
Description The subject starts the exercise from an flexion/extension erect position Bends the trunk forward around waist height with the hands reaching for the toes (lumbar spine flexion) and straight knees Moves the trunk to an erect position Places the hands around the waist Bends the trunk backward as far as possible (lumbar spine extension) The subject returns to initial posture The subject begins from an erect position Places the hands around the waist Bends the trunk laterally to one side with straight knees Moves the trunk to an erect posture Bends it laterally to the other side The subject resumes the initial posture The subject begins from an erect position Places the hands around the waist Rotates the trunk laterally to one side with straight knees Moves the trunk to an erect posture Rotates it laterally to the other side The subject resumes the initial posture At the beginning of the exercise, the subject lies down on the floor Moves the trunk up then forward with the hands reaching for the toes The subject resumes the initial position The subject stans the exercise from an erect position with the foreanns perpendicular to the trunk and the upper arms vertical (parallel and adjacent to the trunk) Flexes the wrist Extends the wrist The subject resumes the initial position The subject stans the exercise from an erect position with the forearms perpendicular to the trunk and the upper arms vertical (parallel and adjacent to the trunk) Pronates the forearm around the elbow Supinates the forearm around the elbow The subject resumes the initial position The subject starts the exercise from an erect position with the upper extremity venical (parallel and adjacent to the trunk) Hexes the upper extremities around the shoulder Extends the upper extremities around the shoulder The subject resumes the initial position the subject starts the exercise from an erect position The subject bends the knees with straight back and hands around the waist The subject resumes the initial position The subject starts the exercise by standing on knees with straight back, lower legs parallel to the thighs, and angle flexed on the floor Flexes the trunk forward until the forehead gets close to the floor In the position taken in step 2, the hands touch the floor (bent around the wrist) The subject resumes the initial position
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Table 3. Frequency and holding time of flexibility exercises for various training groups
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Group No.
Frequency of flexibility exercise week I week 2 week 3 week4
week 1
Holding lime week 3
week 2
week 4
resistance exercise was used (Genaidy et al. 1990). The 10 RM load was defined as the maximum load that an employee could handle ten consecutive times without resting between the repetitions for the task under consideration. The ten-repetition maximum technique required the subject to perform a total of 30 repetitions per training session divided into three sets of ten repetitions each as folIows: (1) set 1= 10 repetitions at a load of 112 the.10 RM load; (2) set 2= 10 repetitions at a load of 314 the 10 RM load; (3) set 3-1 10 repetitions at a load equal to the 10 RM load. The subject was asked to continue training at the 10 RM load until he was able to perform twelve repetitions of set 3, then the I0 RM load was increased by 4 kg for the overall body manual material handling task and 2 kg for the upper extremity manual handling task and was considered as the new 10 RM load for the next training session. Two minutes of rest was provided between two consecutive sets.
3.3.3. Evaluation of training protocols: Each employee was tested twice, separated by a period of four weeks. The various tests included dynamic and static strength, muscular endurance, and flexibility. The tests were conducted in the week prior to the start and the week after the end of the intensivelshort training programme. The muscular endurance test required each employee t o perform the overall body manual material task described in the previous section until he/she could not perform it any longer due to local muscular fatigue andlor overall body fatigue. The test duration was defined as endurance time, and was recorded upon termination of the exercise. Each subject handed a load equal to 75% of the subject's initial dynamic strength and contained in a 38 cm x 38 cm x 25 cm box. Dynamic strength was defined as the maximum amount of load contained in a 38 cm x 38 cm x 25 ern box that could be handled for the overall body manual material handling task through a single trial. For each static measurement, the subject was attached to a handle connected to a load cell which is hooked to an electronic device with a digital readout to measure the exerted force. Static strength measured were recorded according to the procedures reported by Ayoub et al. (1977). The flexibility measurements consisted of: (1) sit and reach, (2) truncal rotation; (3) lateral bending; and (4) lumbar spine extension. Each test was repeated three times, with thirty seconds of rest between trials for the same test and 2 min of rest between two consecutive tests. The final score for each test was the average of the three trials. Before any starting any test, a warm-up of five stretches was performed by each subject. The sit and reach test followed the guidelines of Wilmore (1 986). Lateral bending was examined by recording the difference between the position of the fingertips in erect standing and in maximal side bending to the right and left sides (Battie et a/.
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1987). The subject was instructed to keep the knees straight and both heel on the floor when bending to the side. The lumbar spine extension was measured in a standing position using a goniometer which was placed on the first lumbar vertebra. In the truncal rotation test, leftlright truncal rotation was measured by attaching a belt around the subject's chest. A pointer was connected to the belt so that it recorded the angular rotation of the spine. 3.4. Design and evaluation offollow-up programme The objective of follow-up training was to sustain the improved performance that may be gained from the shortlintensive training programme. A flexibility exercise programme was implemented at the beginning of the shift twice a week. The duration of the follow-up programme was four weeks. The programme consisted of the exercises described in table 2. For groups 1 and 3, each exercise was repeated 12 times with a count of 9 at the final position. For groups 2 and 4, each exercise was performed 7 times with a count of 14 at the final position. The evaluation of the follow-up programme was performed in the week following the completion of the follow-up protocol. The same dependent variables collected during the intensive/short training programme were also measured at this time. For each group, measurements collected prior to the start of the follow-up programme were compared to those obtained at the end of the programme.
3.5. Data analysis Several approaches can be used for the statistical analysis of the data obtained in the present investigation. Huck and McLean (1975) recommended that, for a pretest-post-test design, analysis of covariance should be used to assess the degree to which the four study groups differed in response measures at the end of the intensivelshort training or follow-up training protocol. The post-test response measure served as the dependent variable while the pre-test value served as the covariate. Analysis of covariance was conducted for each response measure. An analysis of variance was conducted for each experimental group in order to determine whether there was a significant change from pre-treatment to posttreatment for each rcsponse variable (Asfour et al. 1990). The analysis of covariance and variance were conducted using the General Linear Model Procedure 'GLM'of the Statistical Analysis System Software (SAS 1 985). 4.
Results
4 . 1 . Descriptive sfatistics
Means and standard deviations of response measures for the intensivelshort training programme are given in table 4. Post-test flexibility measures, dynamic strength, and endurance time increased with respect to the pre-test measures among all training groups. The average gains in flexibility measures due to training for groups 1, 2, 3, and 4 were 26%, 29%, 26%, and 20%, respectively. A minimum improvement of 99% was achieved in terms of endurance time. The average percentage increase in dynamic strength ranged from 28% to 59%. Post-test static strength measures were higher than the pre-test measures for the second flexibility group and the strengthflexibility groups. Less gains were obtained for the first flexibility group. The average percent increase in static strength was 6%, 17%, 25%, and 30%, respectively, for groups 1, 2, 3, and 4.
Flexibility and dynamic strength Table 4.
Descriptive statistics of response measures for in tensivehhort training programme.
Group response measure
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I
1111
Pre-test SD mean
Post-test mean SD
Percentage change
Group 1 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) cm Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 2 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 3 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach Lateral bending (right) Lateral bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 4 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (crn) Lateral bending (right) (deg.) Lateral bending (left) (deg.) Rotat ion (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Note: Group I-first flexibility group; Group 2-second flexibility group; Group 3-first strength-flexibili ty group; Group 4-second strength-flexibili ty group.
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The means and standard deviations of the response measures for the follow-up training programme are given in table 5. There was a loss in flexibility for both flexibility protocols. The average loss was 1 1 % and 7016, respectively for b o ~ h protocols. Static strength was not affected. The average percentage change was 2.3% and 0.4% for both flexibility protocols, respectively. Sim-ilar results were obtained in terms of dynamic strength and dynamic endurance. However, dynamic endurance increased 24% for the second flexibility protocol. Table 5. Descriptive statistics of response measures for follow-up training programme. Pre-test mean SD
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Group response measure
Post-test SD mean
Percentage change
Group I Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) tateral bending (right) Literal bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Group 2 Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateral bending (right) Lateral bending (left) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Note: Group I -first
flexibility group; Group 2-second
flexibility group.
4.2. Analysis of variance and covariance The results of analysis of covariance for the intensive/short training protocol are summarized in table 6, and indicate that: (1) there were no significant differences between the flexibility group; (2) there were no significant differences between the strength-flexibility groups, except endurance time where the second strength-flexibility protocol yielded higher gains; (3) the first strength-flexibility group resulted only in significantly higher static arm and dynamic strength values than the first flexibility group, and endurance time was higher for the second strength-flexibility group than the second flexibility group. No other differences were found between the two groups. The analysis of variance results showed that dynamic strength and endurance time
Flexibility and dynamic strength were statistically significant for all training groups (tabje 7). In the post-test, most flexibility measures were significantly higher than those in pre-tests. Static strength was significantly improved for all groups, except the first flexibility group which did not experience any significant change. Table 6. Analysis of covariance results for various groups in intensivelshort training programme.
Response measure
Significance level G3 G1 G2 vs vs vs vs G2 G 4 G3 G 4
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Endurance time (min) Sit and reach (cm) Lateralbending(right)(cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg) Lumbar spine extension (deg.)
NS NS NS NS S NS NS NS NS NS NS NS
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Gf
GI
NS NS NS
NS NS NS NS NS NS NS
NS
NS
NS
82
NS
NS
NS
37
NS
NS
Groups G2 G3
429 477 533 586 622 619 1036 1097 1153 1382 1394 1580 424 505 527 10-3 10 11.4 25 26 28 22 27 27
S NS NS NS S NS NS NS NS NS
NS NS NS NS NS S
NS NS
.
26 84
G4 549
609 1123
1720 475
26
23
16 27 24 23
84 91 36
84 85
84 82
37
37
Note: Adjusted means of response variables are reported.
Table 7. Analysis of variance results for intensivelshort training programme. Response measure
GI
Groups G2 G3
G4
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
Nole: G !-Group i ; G2-Group 2: G3-Group 3; G4-Group 4; S-statistically cant at the 5% level; NS-statistically non-significant at the 5% level.
signifi-
For the follow-up protocols, the analysis of covariance indicated no significant differences between the two training groups in terms of static and dynamic strength, and all flexibility measures (table 8). Endurance time was significantly higher for the second flexibility group. No significant differences were found between the pre-test
.
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and post-test measures of static and dynamic strength for both flexibility protocols (table 9). O n the other hand, significant differences were obtained in terms of flexibility measures for both flexibility protocols. Table 8. Analysis of covariance results for follow-up training programme.
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Response measure
Significance level
Adjusted means G1 G2
Static arm strength (N) Static shoulder strength Static back strength (N) Static composite strengt Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (leh) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.) Nore: Adjusted means of response variables are reported.
Table 9. Analysis of variance results for follow-up training programme. Groups Response measure
G1
G2
Static arm strength (N) Static shoulder strength (N) Static back strength (N) Static composite strength (N) Dynamic strength (N) Dynamic endurance (min) Sit and reach (cm) Lateral bending (right) (cm) Lateral bending (left) (cm) Rotation (right) (deg.) Rotation (left) (deg.) Lumbar spine extension (deg.)
5. Discussion Most physical training studies on manual material handling tasks were conducted on college students. This study utilized as subjects hospital management workers who were engaged in various types of manual handling tasks over an eight-week period. In the first four weeks,.employees were divided into four groups and each group was given a different training protocoi. All protocols were designed to permit comparison among the four training groups. In the following four weeks of the study, employees were split into two groups.
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5.1. Inrensive/short programme ' Both flexibility training groups resulted in significant improvement in dynamic strength, endurance time, and flexibility measures during the course of intensive1 short training. Static strength was only improved for the second flexibility group. Overall, no significant differences were found between the two protocols except for the dynamic strength. In general, it seems that by progressively increasing the number of exercise repetitions or holding time, similar improvement in physical capacity could be obtained. The results obtained from the flexibility groups are comparable to those obtained in Genaidy (1 99 1 b) for college students. Genaidy ( 1 99 1b) reported a 20.2Oh increase in truncal rotation, 2 1.4% improvement in low back flexibility, and 36.5% change in dynamic strength for male college students following a 4-week training programme. In this study, there was 28.4%, 28-3%, and 39% improvement in truncal rotation, low-back flexibility (sit and reach) and dynamic strength, respectively, for the flexibility groups. Each strength-flexibility training protocol resulted in significant improvement in employees' physical capacity. Moreover, no significant differences were obtained between the two groups for each dependent variable, except for dynamic endurance where the second protocol resulted in higher values. Thus, such strength-flexibility protocol was equally effective in improving physical capacity. The strength-flexibility protocol used in Genaidy et al. ( 1 991) scored high gains in dynamic strength (85.8%), endurance time ( I 24-2%), and low back flexibility (48-4%), comparable to those obtained in this study for the strength-flexibility groups (improvements in dynamic strength-52.4%; endurance time- 1 50.2%; and low back flexibility-27.2%). There was no major differences between the strength-flexibility and flexibility groups in terms of physical capacity. This could be interpreted in two different ways. A flexibility protocol may be as effective as the strength-flexibility protocol in improving physical capacity. On the other hand, the 4-week duration of training may be too short to detect any substantial differences since the strengt h-flexibility protocols generally resulted in greater performance improvement than the flexibility protocols. Finally, employees reported that, after the first week of training, they started to feel the positive effects of exercise during leisure time. They reported engaging in many activities without being fatigued. Thus, it seems that exercise may have both physical and psychological effects on employees. In this study, the physical effects were only recorded. Therefore, future studies should test if exercise has any psychological effects. Sime ( 1 984) pointed out that those who exercise regularly have reported reduced anxiety and depression, improved mood and self-esteem, and a better sense of self-control.
5.2. Follow-up programme Both static and dynamic strengths remained almost unchanged during the course of the follow-up programme. On the other hand, there was a loss in flexibility measures. Significant losses were found for some flexibility measures, with more pronounced losses for the flexibility protocol. These results indicate that a follow-up flexibility exercise protocol performed at a rate of 2 timeslweek is not adequate to maintain the gains obtained from the intensivelshort training programme. Thus, it is suggested that a follow-up flexibility training protocol should be performed on a daily basis.
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5.3. General observations The flexibility and strength-flexibility training protocols produced comparable effects on the physical capacity of employees within the 4-week period investigated in this research. It seems that this period should be extended in order to determine the desired role of each protocol in improving human capability. There are different views regarding improving human capability through flexibility and strength training protocols. Hartley-O'Brien ( 1 980) suggested that flexibility may be increased by either decreasing the resistance of target muscle or increasing the strength of opposing muscles. Physiologically, resistance to stretch may be decreased in two ways: (1) by actual physical lengthening of the connective tissues; and (2) by relaxation of the muscle under stretch. Increasing the strength of the muscles that will activate the range of motion can be achieved by various muscle loading activities as well as by reflexive facilitatory techniques. Chapman er a/. (1 972) reported that progressive, resistance exercise improved the strength and joint mobility of the index fingers. Massey and Chaudet ( 1 955) pointed out that progressive resistance may increase the range of motion in joints exercised, while it may actually restrict movements in areas that are not exercised. They attributed this phenomenon to an imbalance in development of the muscles surrounding or affecting the movement of a joint. 6. Conclusions The results of this study showed that significant improvements in physical capacity could be achieved through a flexibility training programme. Improvement in physical capacity can be assured either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase in exercise repetition with fixed holding time. The progressive increase in holding time yielded slightly higher values. No significant differences were found between the flexibility and strengthflexibility training protocols in terms of physical capacity. However, the strengthflexibility protocols resulted, on the average, in higher percent improvement in physical capacity. A follow-up performed at a rate of 2 timedweek is not adequate to maintain the performance levels gained from the initial training, thus, it is suggested that a follow-up flexibility protocol should be performed on a daily basis to sustain these gains. Finally, no major differences were obtained among the two flexibility protocols during the follow-up programme. However, the progressive increase in holding'time resulted in less losses in terms of flexibility. References ASFOUR, S. S., AYOUB,M . M. and M r r a , A. l984a, EfTects on an endurance and strength
training programme on lifting capacity of males, Ergonomics, 27, 435-442. ASFOUR,S. S., DUTTA,S. P. and TABOUN, S. M. 1984b, The effects of training on static strength and carrying capacity of college males, in: A. Mital, Trends in Ergonomics/Human Factors I (Elsevier Science Publishers, Amsterdam), 1 6 1-1 66. ASFOUR,S. S., KHALIL,T.M., WALY, S. M., GOLDBERG, M. L., ROSOMOFF, R. S. and Roso~om,H. L. 1990, Biofeedback in back muscle strengthening, Spine, 15, 510-513. ASSOCIATION OF SCHOOLSOF PUBUCH ULTH 1 9 86, Propos~dNational Strategiesfor !he Prevmtion of Leading Work-related Diseases and Injuries, Pad I , prepared for National Insti tute for Occupational Safety and Health (Cincinnati, OH), Pb87- 1 14740; reprinted by US Depanment of Commerce, National Technical Information Service. AYOUB,M. M., DEIVANAYAGAM, S. and BAKKEN,G . 1977, A preliminary manual for selected an thropometric strength and endurance measurement. Texas Tech University Report, Texas Tech University, Lubbock, TX.
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h m ~ M. , C., BIGOS, S. J., SHEELY, A. and WORTLEY, M. D. 1987, Spinal flexibility and individual factors that influence it, Physical Therapy, 67, 653-658. CADY,L. D., B r m o m , D. P., O'CONNELL,E. R., THOMAS, P. C. and A w , J. H. 1979, Strength and fitness and subsequent back injuries in fire fighters, Journal of Occuparional Medicine, 21, 269-272. E. A., DE VRIES,H. A. and SWEZEY, K. 1972, Joint stiffness: effects of exercise on CHAPMAN, young and old men, Journal of Gerontology, 77, 2 1 8-22 1 . C ~ R FOR S DISEASECOKIROL1983a, Leading work-related diseases and injuries-Uni ted States, Morbidity and Mortality Weekly Reporr, 32 (2), 24-26, 32. CENTERS FOR DISEASE COKIROL198 3b, Musculoskeletal injuries, Morbidity and Mortality Weekl-v Reporr, 32( 14), 1 89- 1 9 1. DEHUN, O., BERG,S., ANDERSSON, G. B. J. and GRIMBY, G. 198 1, Effect of physical training and ergonomic counselling on the psychological perception of work and on the subjective assessment of Iow-back insufficiency, Scandinavian Journal ofRehabilitation Medicine, 13, 1-9. GENAIDY, A. M. 199 la, A physical training programme for manual handling operations, Ergonomics, 34, 1 - 1 1 . GENMDY,A. M. 1 99 1b, Truncal flexibility exercise effects on musculoskeletal capability for manual handling tasks, Applied Ergonomics, 22, 1 55- 1 62. GENMDY, A. M., BAMA,K. M., SARMIDY, R. and SXNA,P. 1 WOa, An endurance training program for symmetrical and asymmetrical manual lifting tasks, Journal oJOccupationa1 Medicine, 32, 226-2 33. GENAIDY, A. M., DAVIS,N., D E L G E., ~ ,GARCIA,S. and AL-HERUIU, E. 1992, Musculoskeletal exercise effects on employees performing manual handling operations in manufacturing industry, Ergonomics, in press. GENAIDY. A. M., GUPTA,T., and ALSHEDI, A. 1990b, Improving human capabilities for combined manual materials handling through a short and intensive physical training program, American lndusrrial Hygiene Association Journal, 51, 810-814. GENMDY,A. M., MITAL, A., and BAFNA,K. 1989, A n endurance training programme for frequent manual carrying tasks, Ergonomics, 32, 149-155. S. .I. 1980, Six mobilization exercises for active range of hip flexion, HARTLEY-O'BRIW, Research Quarterly for Exerci-ye and Sport, 51, 625-63 5. HILYER, J. C., BROWN,K. C., SIRES,A. T.,and PEOPLES,L. 1990, A flexibility intervention to reduce the incidence and severity of joint injuries among municipal firefighters, Journal of Occupational Medicine, 32, 63 1-637. HUCK, S. W. and MCLEAN, R. A. 1975, Using a repeated measures ANOVA to analyse the data from a pre-test-post-test design: a potentially confusing task, Psychological Bulletin, 82, 5 1 1-518. MASSEY, B. H. and CHANDET, N. L. 1956, Effects of systematic, heavy resistive exercise on range of joint movement in young male adults, Research Quarterly, 27, 4 1-5 1. NATIONAL INSTITUTE FOR OCCUPATIONAL S m AND HEALTH 1 98 1, Work Prac!ices Guide for Manual Lifring. DHHS (NOSH), Publication No. 8 1-1 22, March. SILVERSTEM, B. A., A R M ~ R O NT.GJ., , LONGMATE,A. and WOODY,D. 1 98 8, Can in-plant exercise control musculoskeletal symptoms? Journal of Occupational h4edicine, 30, 922-92 7. SIME,W. E. 1 984, Psychological benefits of exercise training in the healthy individual, in J. D. Matarazzo (ed.) Behavioral Healrh: A Handbook of Health Enhancement and Disease Prevenrion (John Wiley and Sons, New York), 488-508. S T A T I ~ UANALYSIS L SYSTEM1 985, SAS User's Guide: Statistics, Version 5 (SAS Institute Inc., Cary, NC). WILMORE, J. H. 1 986, Sensible Fitness, Second Edition (Leisure Press, Champaign, Ill). Rcccivcd 20 September 1 99 1. Revision accepted 10 December 1991.
