The
painful shoulder during freestyle swimming
An electromyographic muscles MARY LYNN
cinematographic analysis of twelve
SCOVAZZO, MD, ANTHONY BROWNE, MD, MARILYN PINK,* MS, PT, FRANK W. JOBE, MD, AND JOHN KERRIGAN, MSE
From the Biomechanics
Laboratory,
Centinela
javelin throwers, and 7% of professional golfers (Ref. 6; Centinela Hospital Biomechanics Laboratory, unpublished data, 1988). The golf swing, tennis stroke, volleyball serve, javelin throw, and baseball pitch have all been analyzed with EMG and cinematography. The analysis of swimming has been hampered by unique instrumentation problems such as the
ABSTRACT The purpose of this paper is to describe the patterns of activity of 12 shoulder muscles in painful shoulders, and compare those patterns of activity with normal shoulders. The results show significant differences in 7 of the 12 muscles. Those muscles included the anterior deltoid, middle deltoid, infraspinatus, subscapularis, upper trapezius, rhomboids, and the serratus anterior. There were no significant differences between muscle activity patterns of normal versus painful shoulders in the latissimus dorsi, pectoralis major, teres minor, supraspinatus, or the posterior deltoid. This information will contribute to the development of muscle conditioning programs to optimize performance and prevent injury, as well as develop programs for scientific rehabilitation strengthening.
water-electrode interface and harnessing.I-3.5, 7,8,11 Those instrumentation problems have now been overcome and published in a report on 12 muscles in the normal shoulder during freestyle swimming.I2 That study outlined the specific role of each of the muscles and the synchrony of motion in the stroke. The crucial question remains, however, of the differences between the normal and painful shoulder during the freestyle stroke. Thus, this study was designed to describe the painful shoulder during freestyle swimming and to compare it to the normal shoulder.
MATERIALS AND METHODS
swimmers cover 10,000 to 14,000 meters a day miles), 6 to 7 days a week. Some distance swimmers far as 24,000 meters a day. This equates to 16,000
Competitive (6
to 8
go
as
Hospital Medical Center, Inglewood, California
Subjects
shoulder revolutions per week. Comparably, there are approximately 1000 shoulder revolutions per week for a professional tennis player or baseball pitcher, 300 revolutions per week for a college javelin thrower, and 200 per week for a 6 professional golfer on the circuit. As with all sports demanding such stress, the swimmer’s shoulder will show signs of wear and tear. Shoulder problems are reported in 66% of elite swimmers, 57% of professional pitchers, 44% of college volleyball players, 29% of college
Fourteen collegiate and masters level competitive swimmers volunteered for this study. All swimmers completed a questionnaire about their history of episodes of shoulder pain and any former diagnosis or treatment rendered. Determination of &dquo;painful&dquo; was based on the subject’s answer to the question of whether he or she was currently having any pain, and was confirmed by physical examination checking for signs of shoulder instability, apprehension, and impingement. Subjects who had past episodes of pain, but were now asymptomatic were excluded from this population. The swimmers had an average of 11 years of competitive swimming experience, and were currently training 2500 to
* Address correspondence and repnnt requests to’ Manlyn Pink, MS, PT, Biomechanics Laboratory, Centinela Hospital Medical Center, 555 East Hardy Street, Inglewood, CA 90301.
577
578
4000 yards per day, 3 to 5 days per week. Fifty percent of the subjects noted the freestyle stroke as their best stroke. The mean age of the swimmers was 31 years; there were nine male swimmers and five female swimmers.
Procedure Twelve shoulder muscles were selected for this study, and were divided into two groups of six each. Group A muscles included the anterior, middle, and posterior deltoids, serratus anterior, upper trapezius, and rhomboids. Group B muscles included the subscapularis, supraspinatus, infraspinatus, teres minor, latissimus dorsi, and pectoralis major. Group A muscles were monitored in five shoulders, and Group B muscles in nine shoulders. Testing was done in one of two pools that were equipped with underwater windows. Motion was filmed from two lateral high speed cameras: one underwater view and one surface view. The EMG signal was recorded with fine wire electrodes. The technique for preparation, recording, and processing is reported in our study on normal shoulders.&dquo; Data for 6 to 12 stroke cycles per swimmer was obtained. The freestyle stroke was divided into 25 parts based on time. The film was synchronized with the EMG to discern four phases. The four phases, and the number of subdivisions per phase were as follows. 1. Early pull through: beginning with hand entry into the water and ending when the humerus was perpendicular to the axis of the torso (12 subdivisions). 2. Late pull-through: beginning at the completion of
early pull-through and ending as the hand left the water (seven subdivisions). 3. Early recovery: beginning at hand exit and ending when the humerus was perpendicular to the water surface (four subdivisions). 4. Late recovery: beginning at the completion of early recovery and ending at hand entry (two subdivisions). Data analysis was carried out as described in our paper on
normal shoulder muscle
activity.&dquo;
group
were
of each muscle to determine whether there were any statistically significant differences between the painful and normal shoulders (P < 0.10).
RESULTS Deltoids The patterns of muscular activity in the three heads of the deltoid were similar in the painful and normal shoulders (Table 1). However, both the anterior and middle deltoids had significantly less activity in the painful shoulder during hand entry as well as during hand exit. The anterior deltoid in the painful shoulders revealed between 3% and 16% manual muscle test (MMT) as the hand entered the water and reached forward, and between 30% and 39% MMT as the hand was exiting; whereas in the normal shoulders, the intensity was between 13% and 45% MMT as the hand entered and reached, and between 66% and 76% MMT as
TABLE 1 Muscle
activity at
25
The data from the
compared to the normal data collected in that study. Independent t-tests were done for every phase
painful
points during the freestyle stroke
in
painful shoulders
579
respectively)
in the
posterior deltoid before hand exit (Fig.
1). Rotator cuff
infraspinatus in the painful shoulders exhibited significantly more activity at the end of pull-through than did the normal shoulders (20% to 32% MMT compared to 7% to 11% MMT) (Fig. 2, Table 1). The subscapularis in the subjects with shoulder pain had significantly less activity at midrecovery (26% to 35% MMT as opposed to 67% to 71% MMT in the normal shoulders) (Fig. 2, Table 1). There were no statistically significant differences between the painful
The
and normal shoulders in the supraspinatus or the teres minor (Fig. 2, Table 1).
Scapular muscles All three scapular rotators demonstrated statistically significant differences between the painful and normal groups. Both the rhomboids and upper trapezius had less activity at hand entry in the painful group (11% and 24% MMT, respectively, as compared to 49% and 64% MMT in the normal group) (Fig. 3). In addition, the rhomboids revealed significantly more activity in the painful group during middle pull-through (34% to 65% MMT as compared to 9% to 32% MMT in the normal group). At this same point, the serratus anterior was significantly less active in the painful group as compared to the normal group (10% to 18% MMT as opposed to 33% to 41% MMT). The serratus anterior in the painful shoulders also had significantly less activity shortly after hand entry (9% to 10% MMT, as compared to 21% to 28% MMT in the normal shoulders) (Fig. 3). Shoulder extensors The patterns of activity in the pectoralis major and latissimus dorsi for both the painful and normal shoulders revealed no statistically significant differences (Table 1). The peak activity in the pectoralis major was 71% MMT ± 32 in the normal shoulder and 71% MMT ± 27 in the painful shoulder, and in the latissimus dorsi it was 75% MMT ± 49 in the normal shoulder and 61% MMT ± 51 in the painful shoulder (Fig. 4). 1. Muscle activity of the deltoids in the painful and the normal shoulders. Vertical lines show periods of significant difference.
Figure
the hand exited (Fig. 1). The middle deltoid in the painful shoulders exhibited 9% to 19% MMT as the hand was entering and 28% MMT just prior to hand exit. In contrast, the normal shoulder activity was between 41% and 51% MMT at hand entry and 54% MMT just prior to hand exit (Fig. 1). The posterior deltoid demonstrated no significant differences between the painful and normal shoulders. Both groups exhibited peaks of activity (61% and 72% MMT,
DISCUSSION
Pull-through The events selected on the film to mark pull-through were chosen because they were repeatable observations. Yet, there were different phases within pull-through. From the point that the hand entered the water to the point of maximal elbow extension, there was no actual pulling. The first part of &dquo;pull-through&dquo; was really reaching and gliding. The pulling action began after the reach, and actually stopped when the palm approached the thigh. Once the palm was at the thigh, it rotated inward so that it could exit the water with
580
points (i.e., maximal reach and consistently and accurately identified on the film. Thus, the phases were subdivided according to the identifying event. The swimmers with painful shoulders had a different minimal
drag.9
These ideal
palm rotation) could
not be
pattern of hand entry than did those with normal shoulders. The hand entered further away from midline, and the humerus was lower to the water. Coaches note this position as a dropped elbow position and remark that they can tell when a swimmer is hurt (or &dquo;tired&dquo; or &dquo;lazy&dquo;) because they fail to hold the elbow up. This was consistent with the significant decrease in activity in the anterior and middle deltoids. Also, the scapula would not need to be upwardly rotated nor retracted as much in this position. Accordingly, there was significantly less activity in the upper trapezius and rhomboids. This position of hand entry avoids the classic impingement position of flexion and internal rotation of the humerus described by Neer and Welsh&dquo; and Hawkins and Kennedy4. The swimmers with painful shoulders also showed differences in their muscle activity during pulling when compared to normal shoulders. First of all, the serratus anterior in the painful shoulders was not as active as it was in the normal shoulders during the powerful propulsive phase.l2 The role of the serratus anterior in the normal shoulders was to upwardly rotate and protract the scapula. Once the scapula was in this position, at the beginning of pulling, it effectively reversed the origin and insertion and was used to pull the body over the arm (thus propelling the body through the water). If the serratus anterior fatigued, it would be unable to add to this propulsive motion. The position of protraction and upward rotation also avoids impingement of the rotator cuff and biceps tendon beneath the coracoacromial arch. With fatigue of the serratus anterior, the scapula would not keep up with the humerus. Thus, the space between the glenoid and the humerus would increase and lead to insta-
bility. At the exact time that the serratus anterior was dysfunctional and exhibiting abnormally low levels of activity, the rhomboids were exhibiting significantly more in the painful shoulders. Thus, the rhomboids were retracting and downwardly rotating while the serratus anterior should have been doing just the opposite. This was probably due to preparation for early hand exit. In exiting early, the swimmers avoided the extremes of internal rotation that accompany the more fully extended elbow. An early hand exit occurred before the palm passed the thigh, with the elbow bent. In the process of lifting the shoulder out of the water, the scapula must be retracted. To prepare for an early hand exit, the rhomboids must be active during the pulling while the serratus anterior remains inactive. Also, the rhomboids may have been substituting for a fatigued serratus anterior. By retracting the scapula, the rhomboids were attempting to create more space beneath the coracoacromial arch, thereby avoiding impinge-
Figure 2. Muscle activity of the rotator cuff muscles in the painful and the normal shoulders. Vertical lines show periods of significant difference.
581
...&dquo;&dquo;..
Figure 4. Muscle activity of the shoulder extensors in the painful and the normal shoulders. water.9 The infraspinatus demonstrated significantly
more
activity in the painful shoulders as
it externally rotated the humerus. This allowed the swimmer to avoid the painful internal rotation. Also, the anterior deltoid showed significantly less activity as the lifting, abducting, and forward flexing of the humerus was blunted. Once again, the coaches note this as a &dquo;dropped&dquo; elbow. By keeping the arm lower and shortening the arc of motion, these swimmers were avoiding the painful impingement.
Figure 3. Muscle activity of the scapular muscles in the painful and the normal shoulders. Vertical lines show periods of significant differences. Presumably the rhomboids retraction component was greater than the rotation component. Thus, the optimum synchrony of firing seen in normal scapular rotation was disturbed at the time of propulsion. At the end of pull-through, as the elbow left the water and the hand began to exit, another abnormal pattern was seen. ment.
This was the time when normal shoulders were in internal rotation and the muscles were lifting the arm out of the
Recovery The only significantly reduced muscle activity levels found in the painful shoulders were in the anterior deltoid, which is a carry over from the late pull-through and has already been discussed, and in the subscapularis. The subscapularis in the normal shoulders was similar to the serratus anterior in that it never dropped below 20% MMT. Once again, this would suggest that it was susceptible to fatigue. In addition, the subscapularis puts the shoulder in the painful position of internal rotation. Thus, the swimmer may want to avoid that position, and hence the decreased activity.
582
SUMMARY Based on the EMG findings, the following statements summarize the differences between the swimmers with painful shoulders and those with normal shoulders: 1. At hand entry, there was significantly less muscle activity in the rhomboids and upper trapezius, as well as the anterior and middle deltoids in the swimmers with painful shoulders when compared to swimmers with normal shoulders. 2. During pulling, there was significantly less activity in the serratus anterior and significantly more in the rhomboids in those subjects with painful shoulders. 3. At hand exit, there was significantly less muscle activity in the anterior and middle deltoids and significantly more in the infraspinatus in the group with painful shoulders. 4. At midrecovery, there was significantly less muscle action in the subscapularis for the swimmers with painful shoulders. 5. There were no differences in the muscle firing pattern, nor amplitude, between swimmers with painful and normal shoulders in the posterior deltoid, supraspinatus, teres minor, pectoralis major, or latissimus dorsi in the freestyle stroke.
ACKNOWLEDGMENT The authors thank Dr. Jacquelin Perry for her assistance and support throughout this project.
REFERENCES
1
2.
3
4
5.
6. 7
8
JP A review of EMG in swimming Explanation of facts and/or feedback information, in Hollander AP, Huijing P, De Goats G (eds). Biomechanics and Medicine in Swimming Champaign, IL, Human Kinetics, 1983, pp 123-135 Clarys JP, Jiskoot J, Lewillie L: A kinematographical electromyographical, and resistance study of water polo and competition front crawl, in Cerguilini . Basel, S Karger, S, Venerando A, Wartenweller J (eds) Biomechanics III 1973, pp 446-452 Clarys JP, Massez C, Van Den Broeck, et al: Total telemetric surface EMG of the front crawl, in Matui H, Kobayashi K (eds). Biomechanics IXB , Champaign, IL, Human Kinetics Publishers Inc., 1983, pp 951-958 Hawkins RJ, Kennedy JC: Impingement syndrome in athletes Am J Sports Med 8 151-158, 1980 Ikai M, Ishi K, Miyashita M. An electromyographic study of swimming Res J Phys Educ 7 55-87, 1964 Johnson D. In swimming, shoulder the burden, Sportcare and Fitness
Clarys
May-June ( ): 24-30, 1988 Lewillie L: Telemetry of electromyographic and electrogoniometric signals in swimming, in Nelson RC, Moorehouse CA (eds): Biomechanics IV . Basel, S Karger Verlag, 1974, pp 203-207 Lewillie L: Muscular activity in swimming, in Cerquiglini S, Venerando A, Wartenweiler J (eds): Biomechanics III . Basel, S Karger Verlag, 1973, pp 440-445
9
EW: Swimming Faster. Mountain View, CA, Mayfield Publishing Co, 1982 pp 53-99 10. Neer CS, Welsh RP. The shoulder in sports Orthop Clin North Am 18 583-591,1977 11 Okamoto T, Wolf SL Underwater recording of electromyographic activity using fine wire electrodes, in Terands J, Bedingfield W (eds) Swimming III Baltimore, University Park Press, 1979, pp 160-166 12 Pink M, Perry J, Browne A, et al: The normal shoulder during freestyle swimming An EMG and cinematographic analysis of twelve muscles Am J Sports Med 19. 569-576, 1991
Maghscho
painful shoulder during freestyle swimming
An electromyographic muscles MARY LYNN
cinematographic analysis of twelve
SCOVAZZO, MD, ANTHONY BROWNE, MD, MARILYN PINK,* MS, PT, FRANK W. JOBE, MD, AND JOHN KERRIGAN, MSE
From the Biomechanics
Laboratory,
Centinela
javelin throwers, and 7% of professional golfers (Ref. 6; Centinela Hospital Biomechanics Laboratory, unpublished data, 1988). The golf swing, tennis stroke, volleyball serve, javelin throw, and baseball pitch have all been analyzed with EMG and cinematography. The analysis of swimming has been hampered by unique instrumentation problems such as the
ABSTRACT The purpose of this paper is to describe the patterns of activity of 12 shoulder muscles in painful shoulders, and compare those patterns of activity with normal shoulders. The results show significant differences in 7 of the 12 muscles. Those muscles included the anterior deltoid, middle deltoid, infraspinatus, subscapularis, upper trapezius, rhomboids, and the serratus anterior. There were no significant differences between muscle activity patterns of normal versus painful shoulders in the latissimus dorsi, pectoralis major, teres minor, supraspinatus, or the posterior deltoid. This information will contribute to the development of muscle conditioning programs to optimize performance and prevent injury, as well as develop programs for scientific rehabilitation strengthening.
water-electrode interface and harnessing.I-3.5, 7,8,11 Those instrumentation problems have now been overcome and published in a report on 12 muscles in the normal shoulder during freestyle swimming.I2 That study outlined the specific role of each of the muscles and the synchrony of motion in the stroke. The crucial question remains, however, of the differences between the normal and painful shoulder during the freestyle stroke. Thus, this study was designed to describe the painful shoulder during freestyle swimming and to compare it to the normal shoulder.
MATERIALS AND METHODS
swimmers cover 10,000 to 14,000 meters a day miles), 6 to 7 days a week. Some distance swimmers far as 24,000 meters a day. This equates to 16,000
Competitive (6
to 8
go
as
Hospital Medical Center, Inglewood, California
Subjects
shoulder revolutions per week. Comparably, there are approximately 1000 shoulder revolutions per week for a professional tennis player or baseball pitcher, 300 revolutions per week for a college javelin thrower, and 200 per week for a 6 professional golfer on the circuit. As with all sports demanding such stress, the swimmer’s shoulder will show signs of wear and tear. Shoulder problems are reported in 66% of elite swimmers, 57% of professional pitchers, 44% of college volleyball players, 29% of college
Fourteen collegiate and masters level competitive swimmers volunteered for this study. All swimmers completed a questionnaire about their history of episodes of shoulder pain and any former diagnosis or treatment rendered. Determination of &dquo;painful&dquo; was based on the subject’s answer to the question of whether he or she was currently having any pain, and was confirmed by physical examination checking for signs of shoulder instability, apprehension, and impingement. Subjects who had past episodes of pain, but were now asymptomatic were excluded from this population. The swimmers had an average of 11 years of competitive swimming experience, and were currently training 2500 to
* Address correspondence and repnnt requests to’ Manlyn Pink, MS, PT, Biomechanics Laboratory, Centinela Hospital Medical Center, 555 East Hardy Street, Inglewood, CA 90301.
577
578
4000 yards per day, 3 to 5 days per week. Fifty percent of the subjects noted the freestyle stroke as their best stroke. The mean age of the swimmers was 31 years; there were nine male swimmers and five female swimmers.
Procedure Twelve shoulder muscles were selected for this study, and were divided into two groups of six each. Group A muscles included the anterior, middle, and posterior deltoids, serratus anterior, upper trapezius, and rhomboids. Group B muscles included the subscapularis, supraspinatus, infraspinatus, teres minor, latissimus dorsi, and pectoralis major. Group A muscles were monitored in five shoulders, and Group B muscles in nine shoulders. Testing was done in one of two pools that were equipped with underwater windows. Motion was filmed from two lateral high speed cameras: one underwater view and one surface view. The EMG signal was recorded with fine wire electrodes. The technique for preparation, recording, and processing is reported in our study on normal shoulders.&dquo; Data for 6 to 12 stroke cycles per swimmer was obtained. The freestyle stroke was divided into 25 parts based on time. The film was synchronized with the EMG to discern four phases. The four phases, and the number of subdivisions per phase were as follows. 1. Early pull through: beginning with hand entry into the water and ending when the humerus was perpendicular to the axis of the torso (12 subdivisions). 2. Late pull-through: beginning at the completion of
early pull-through and ending as the hand left the water (seven subdivisions). 3. Early recovery: beginning at hand exit and ending when the humerus was perpendicular to the water surface (four subdivisions). 4. Late recovery: beginning at the completion of early recovery and ending at hand entry (two subdivisions). Data analysis was carried out as described in our paper on
normal shoulder muscle
activity.&dquo;
group
were
of each muscle to determine whether there were any statistically significant differences between the painful and normal shoulders (P < 0.10).
RESULTS Deltoids The patterns of muscular activity in the three heads of the deltoid were similar in the painful and normal shoulders (Table 1). However, both the anterior and middle deltoids had significantly less activity in the painful shoulder during hand entry as well as during hand exit. The anterior deltoid in the painful shoulders revealed between 3% and 16% manual muscle test (MMT) as the hand entered the water and reached forward, and between 30% and 39% MMT as the hand was exiting; whereas in the normal shoulders, the intensity was between 13% and 45% MMT as the hand entered and reached, and between 66% and 76% MMT as
TABLE 1 Muscle
activity at
25
The data from the
compared to the normal data collected in that study. Independent t-tests were done for every phase
painful
points during the freestyle stroke
in
painful shoulders
579
respectively)
in the
posterior deltoid before hand exit (Fig.
1). Rotator cuff
infraspinatus in the painful shoulders exhibited significantly more activity at the end of pull-through than did the normal shoulders (20% to 32% MMT compared to 7% to 11% MMT) (Fig. 2, Table 1). The subscapularis in the subjects with shoulder pain had significantly less activity at midrecovery (26% to 35% MMT as opposed to 67% to 71% MMT in the normal shoulders) (Fig. 2, Table 1). There were no statistically significant differences between the painful
The
and normal shoulders in the supraspinatus or the teres minor (Fig. 2, Table 1).
Scapular muscles All three scapular rotators demonstrated statistically significant differences between the painful and normal groups. Both the rhomboids and upper trapezius had less activity at hand entry in the painful group (11% and 24% MMT, respectively, as compared to 49% and 64% MMT in the normal group) (Fig. 3). In addition, the rhomboids revealed significantly more activity in the painful group during middle pull-through (34% to 65% MMT as compared to 9% to 32% MMT in the normal group). At this same point, the serratus anterior was significantly less active in the painful group as compared to the normal group (10% to 18% MMT as opposed to 33% to 41% MMT). The serratus anterior in the painful shoulders also had significantly less activity shortly after hand entry (9% to 10% MMT, as compared to 21% to 28% MMT in the normal shoulders) (Fig. 3). Shoulder extensors The patterns of activity in the pectoralis major and latissimus dorsi for both the painful and normal shoulders revealed no statistically significant differences (Table 1). The peak activity in the pectoralis major was 71% MMT ± 32 in the normal shoulder and 71% MMT ± 27 in the painful shoulder, and in the latissimus dorsi it was 75% MMT ± 49 in the normal shoulder and 61% MMT ± 51 in the painful shoulder (Fig. 4). 1. Muscle activity of the deltoids in the painful and the normal shoulders. Vertical lines show periods of significant difference.
Figure
the hand exited (Fig. 1). The middle deltoid in the painful shoulders exhibited 9% to 19% MMT as the hand was entering and 28% MMT just prior to hand exit. In contrast, the normal shoulder activity was between 41% and 51% MMT at hand entry and 54% MMT just prior to hand exit (Fig. 1). The posterior deltoid demonstrated no significant differences between the painful and normal shoulders. Both groups exhibited peaks of activity (61% and 72% MMT,
DISCUSSION
Pull-through The events selected on the film to mark pull-through were chosen because they were repeatable observations. Yet, there were different phases within pull-through. From the point that the hand entered the water to the point of maximal elbow extension, there was no actual pulling. The first part of &dquo;pull-through&dquo; was really reaching and gliding. The pulling action began after the reach, and actually stopped when the palm approached the thigh. Once the palm was at the thigh, it rotated inward so that it could exit the water with
580
points (i.e., maximal reach and consistently and accurately identified on the film. Thus, the phases were subdivided according to the identifying event. The swimmers with painful shoulders had a different minimal
drag.9
These ideal
palm rotation) could
not be
pattern of hand entry than did those with normal shoulders. The hand entered further away from midline, and the humerus was lower to the water. Coaches note this position as a dropped elbow position and remark that they can tell when a swimmer is hurt (or &dquo;tired&dquo; or &dquo;lazy&dquo;) because they fail to hold the elbow up. This was consistent with the significant decrease in activity in the anterior and middle deltoids. Also, the scapula would not need to be upwardly rotated nor retracted as much in this position. Accordingly, there was significantly less activity in the upper trapezius and rhomboids. This position of hand entry avoids the classic impingement position of flexion and internal rotation of the humerus described by Neer and Welsh&dquo; and Hawkins and Kennedy4. The swimmers with painful shoulders also showed differences in their muscle activity during pulling when compared to normal shoulders. First of all, the serratus anterior in the painful shoulders was not as active as it was in the normal shoulders during the powerful propulsive phase.l2 The role of the serratus anterior in the normal shoulders was to upwardly rotate and protract the scapula. Once the scapula was in this position, at the beginning of pulling, it effectively reversed the origin and insertion and was used to pull the body over the arm (thus propelling the body through the water). If the serratus anterior fatigued, it would be unable to add to this propulsive motion. The position of protraction and upward rotation also avoids impingement of the rotator cuff and biceps tendon beneath the coracoacromial arch. With fatigue of the serratus anterior, the scapula would not keep up with the humerus. Thus, the space between the glenoid and the humerus would increase and lead to insta-
bility. At the exact time that the serratus anterior was dysfunctional and exhibiting abnormally low levels of activity, the rhomboids were exhibiting significantly more in the painful shoulders. Thus, the rhomboids were retracting and downwardly rotating while the serratus anterior should have been doing just the opposite. This was probably due to preparation for early hand exit. In exiting early, the swimmers avoided the extremes of internal rotation that accompany the more fully extended elbow. An early hand exit occurred before the palm passed the thigh, with the elbow bent. In the process of lifting the shoulder out of the water, the scapula must be retracted. To prepare for an early hand exit, the rhomboids must be active during the pulling while the serratus anterior remains inactive. Also, the rhomboids may have been substituting for a fatigued serratus anterior. By retracting the scapula, the rhomboids were attempting to create more space beneath the coracoacromial arch, thereby avoiding impinge-
Figure 2. Muscle activity of the rotator cuff muscles in the painful and the normal shoulders. Vertical lines show periods of significant difference.
581
...&dquo;&dquo;..
Figure 4. Muscle activity of the shoulder extensors in the painful and the normal shoulders. water.9 The infraspinatus demonstrated significantly
more
activity in the painful shoulders as
it externally rotated the humerus. This allowed the swimmer to avoid the painful internal rotation. Also, the anterior deltoid showed significantly less activity as the lifting, abducting, and forward flexing of the humerus was blunted. Once again, the coaches note this as a &dquo;dropped&dquo; elbow. By keeping the arm lower and shortening the arc of motion, these swimmers were avoiding the painful impingement.
Figure 3. Muscle activity of the scapular muscles in the painful and the normal shoulders. Vertical lines show periods of significant differences. Presumably the rhomboids retraction component was greater than the rotation component. Thus, the optimum synchrony of firing seen in normal scapular rotation was disturbed at the time of propulsion. At the end of pull-through, as the elbow left the water and the hand began to exit, another abnormal pattern was seen. ment.
This was the time when normal shoulders were in internal rotation and the muscles were lifting the arm out of the
Recovery The only significantly reduced muscle activity levels found in the painful shoulders were in the anterior deltoid, which is a carry over from the late pull-through and has already been discussed, and in the subscapularis. The subscapularis in the normal shoulders was similar to the serratus anterior in that it never dropped below 20% MMT. Once again, this would suggest that it was susceptible to fatigue. In addition, the subscapularis puts the shoulder in the painful position of internal rotation. Thus, the swimmer may want to avoid that position, and hence the decreased activity.
582
SUMMARY Based on the EMG findings, the following statements summarize the differences between the swimmers with painful shoulders and those with normal shoulders: 1. At hand entry, there was significantly less muscle activity in the rhomboids and upper trapezius, as well as the anterior and middle deltoids in the swimmers with painful shoulders when compared to swimmers with normal shoulders. 2. During pulling, there was significantly less activity in the serratus anterior and significantly more in the rhomboids in those subjects with painful shoulders. 3. At hand exit, there was significantly less muscle activity in the anterior and middle deltoids and significantly more in the infraspinatus in the group with painful shoulders. 4. At midrecovery, there was significantly less muscle action in the subscapularis for the swimmers with painful shoulders. 5. There were no differences in the muscle firing pattern, nor amplitude, between swimmers with painful and normal shoulders in the posterior deltoid, supraspinatus, teres minor, pectoralis major, or latissimus dorsi in the freestyle stroke.
ACKNOWLEDGMENT The authors thank Dr. Jacquelin Perry for her assistance and support throughout this project.
REFERENCES
1
2.
3
4
5.
6. 7
8
JP A review of EMG in swimming Explanation of facts and/or feedback information, in Hollander AP, Huijing P, De Goats G (eds). Biomechanics and Medicine in Swimming Champaign, IL, Human Kinetics, 1983, pp 123-135 Clarys JP, Jiskoot J, Lewillie L: A kinematographical electromyographical, and resistance study of water polo and competition front crawl, in Cerguilini . Basel, S Karger, S, Venerando A, Wartenweller J (eds) Biomechanics III 1973, pp 446-452 Clarys JP, Massez C, Van Den Broeck, et al: Total telemetric surface EMG of the front crawl, in Matui H, Kobayashi K (eds). Biomechanics IXB , Champaign, IL, Human Kinetics Publishers Inc., 1983, pp 951-958 Hawkins RJ, Kennedy JC: Impingement syndrome in athletes Am J Sports Med 8 151-158, 1980 Ikai M, Ishi K, Miyashita M. An electromyographic study of swimming Res J Phys Educ 7 55-87, 1964 Johnson D. In swimming, shoulder the burden, Sportcare and Fitness
Clarys
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