Perceptrral and Motor
Skills, 1979, 49, 475-479. @ Perceptual and Motor Skills 1979
MAINTENANCE OF UNCUED ISOMETRIC CONTRACTIONS BY BLIND AND SIGHTED CLAUDIA G . EMES
The U n i v e r ~ i t yo f Calgary Summa~y.-A comparison of 10 blind and 10 sighted subjects to a proprioceptive task was examined by analysis of response to maintenance o f uncued static contractions. In attempting to sustain hand-grip tensions at specified percentages of maximum voluntary contraction, blind and sighted groups showed no significant difference in performance.
Many rehabilitative techniques in mobiliry, activities of daily living and work, rest on the ability of blind persons to utilize perceptual information. Therefore, knowledge is required about perception and particularly kinesthetic perceptual development of blind individuals. Currently there is no evidence to support the notion that other senses may be heightened to compensate for loss of vision and in fact blind persons frequently demonstrate poor proprioceptive awareness (2, 4 ) . The present study was done to determine the relative performance of blind and noncued, sighted subjecrs on a proprioceptive task. Cain and Stevens ( 3 ) showed that, if subjects attempted to maintain a constant level of perceived work without visual cues, the isometric tension decreased with time. Abraham and Craig ( 1) in a similar study found the same results except where Cain and Stevens used pre-selected starting tensions, Abraham and Craig used a beginning tension which was a fixed percentage of each subject's maximum voluntary contraction. Abraham and Craig suggested that rhe subject's strength may affect the results of uncued tests, therefore the starting tension should be relative to the individual's strength. In the present investigation the question of whether sensory information from the hand played a role in performance was re-examined by comparing results from blind subjects and sighted subjects. This study compared ability to maintain an isometric tension without visual cues for specified periods of rime by both noncued, sighted and blind individuals.
METHOD Physiologists have demonstrated that, when subjects are required to maintain an isometric contraction at a constant level of perceived work without. visual cues, rhe isometric tension will decrease with time (1, 3 ) . It is suggested that the fast component of the tension decline is related to sensory adaptation involving the Golgi tendon organs. Since the Golgi tendon receptors provide proprioceptive information, this method was used to measure the awareness of blind individuals and sighted subjects. As in the work of Abraham and Craig ( I ) , subjects from this study were
476
C. G. EMES
asked to maintain an uncued isometric concraction at 70% maximum voluntary contraction for 30 sec.; 50%, 30% and 15% maximum voluntary contraction of their hand grip for 60 sec. These levels of perceived work were selected because Rohmert (6) found in a detailed study that 70% maximum voluntary concraction could be maintained for 30 sec., 50% for 60 sec., 30% for 2.5 min., and 15% for extended periods of time. The tension record and electromyographic (EMG) activity were recorded during each contraction. Equipment identical to that of Abraham and Craig was used. A hand grip dynamometer with a Wheatstone bridge circuit provided a conrinuous record of tension. The output of the bridge was amplified on a four-channel curvilinear recorder. The hand-grip section was bolted to the top of a table 33 in. high. A steel cable connected the pulling bar of the hand grip to a dynamomecer which was bolted to the floor. In line with the hand grip was a wooden trough in which the subject rested his elbow. The vertical support for the trough was moveable so for a subject seated at an appropriate height next to the table, the trough and vertical support ensured that the relationship of the forearm to the hand grip was constant while the arm was bent at 90" at the elbow. This method of stabilizing the body was effective for isolating the force developed by the forearm flexors ( 1 ) . Two surface electrodes were applied to the volar aspect of the arm over the flexor digitorurn sublimis. The first electrode was 2 cm. distal to the elbow and the intereleccrode distance was 5 cm. A ground electrode was placed midway between the vertebral borders of the scapulae. The EMG signal was rectified and integrated. A Narco PMP-4A model physiograph recorded the electrical activity. Ten blind subjects were selected from the male registry of the Canadian National Institute for the Blind. Five were institutional, five non-institutional and all were over 18 yr. of age. The cause of blindness varied among the subjects; however, all had been blind (less than 10% vision) since birth or within the first three years except for one subject who was blinded at 9 and the sighted group were 10 male college students. The test required performing static hand-grip contractions 1596, 30%, 50%, and 70% of maximum voluntary contraction without visual cues. For each experimental cension the subject repeated three trials. Each set of trials was tested on different days and the order of the tests varied randomly. For each test the subject was instructed to make a maximum voluncary contraction for 2 or 3 sec. The greatest cension of three trials was considered maximum. Rest intervals berween trials were 1 min. Once the maximum voluntary contraction was determined a 5-min. resr was imposed before testing of the percentage contractions began. The 5-min. rest intervals were adequate for complete recovery ( 7 ) .
477
UNCUED ISOMETRIC CONTRACTIONS
Each subject was then instructed to make the appropriate percentage (15, 30, 50 or 7 0 ) contraction of his maximum voluntary contraction and without visual cues, attempt to maintain his original starting tension. The 1596, 30%, and 50% tests lasted for 60 sec. while the 70% test lasted 30 sec.
RESULTS AND D~SCUSSION From Fig. 1 it is evident thac the decline in tension of uncued isometric contractions persisted for both the blind and the sighted groups. Very little difference exists between the groups at the 15 % maximum voluntary contraction. The curves for 30%, 50%, and 70% decline, suggesting that sighted subjects maintained a tension closes to the designated percent of maximum 100 90
SF 30
12
2% I0
* 70
I-"
B& 100 oa s'i a3 90 9 eo m
0
ZO
0
30
40
50
600
10
20
30
40
50
60
TIME IN SECONDS
FIG. 1. Decrease in tension at selected percentages of maximum voluntary contraction (MVC) in uncued tests
voluntary contraction; however, the differences were not significant. The differences between the means of the blind and rhe sighted subjects at the final second of sustained isometric contractions for 30%, 50%, and 70% measures are shown in Table 1. Both groups responded to the rest in the same manner as the uncued subjects of Abraham and Craig's ( 1) study. Without visual cues isometric tension can not be maintained. Other investigators (1, 3, 5 ) have questioned the contribution of fatigue to tension loss during uncued tests. Abraham and Craig (1) showed thac electrical activity, as monitored on the TABLE 1 MEANSOF BLINDAND SIGHTED SUBJECTS A T FINALSECOND OF SUSTAINED ISOMETRICCONTRACTIONS Group
n
M
Blind Sighted
9 10
30% (60 sec.) S D 6
75.3 77.1
31.8 10.8
0.38
50% (60 sec.) M S D t 74.5 82.6
15.8 13.4
1.15
70% (30 sec.) S D t
M
81.1 87.3
19.5 9.6
0.83
478
C. G. EMES
integrated EMG trace, decreased during uncued tests. Because an increase in electrical activity suggests muscle fatigue is occurring, a decrease in electrical activity suggests that a process other than fatigue is occurring ( 8 ) . In the present study fatigue was also studied using EMG traces and the blind and sighted subjects were compared on this factor.
FIG. 2. EMG record for uncued, isometric contraction at 30%, 50%, and 70% of maximum voluntary contraction
Fig. 2 shows that fatigue was probably not a significant factor only in the first 30 sec. of the 30% and 50% tests; however, the slope of the integrated EMG curve indicates that fatigue was involved in the tested response. At 50% of the maximum voluntary contraction sighted subjects showed a definite increase in electrical activity during the final 30 sec. of contraction while blind subjects showed a slight increase at the 30% level. These results do not differ from those of previous investigators ( 1, 3). EMG responses differed slightly between the two groups of this study which may be related to the small sample number (10 sighted, 10 blind) however other similar studies have used even smaller samples
(1,3,5). At the 70% level fatigue is believed to be dominating ( 1 , 3, 5 ) . The responses of the blind and sighted groups were not different. The two EMG
UNCUED ISOMETRIC CONTRACTIONS
479
readings at 15 and 30 sec. do not give a clear picture of a fatigue pattern. Generally the responses as demonstrated on a tension vs time plot plus an EMG trace show that blind subjects had no greater or less awareness of uncued isometric tension than sighted subjects. 1. ABRAHAM, W., &
REFERENCES CRAIG, A. B., JR Tension decline during isometric contractions
without visual cues. Medicine and Science i n Sports, 1975, 7, 99-104. 2. BARICK, H. P., FITTS,P. M., & SNETDBR,R. Reproduction of simple movements as a function of factors influencing proprioceptive feedback. Journal o f Experirnedal Psychology, 1955, 49, 445-454. 3. CAIN.W. S., & STEVENS, J. C Constant-effort contraction related to the electromyogram. Medicine and Science i n Sports, 1973, 5, 121-127. 4. LINDLEY,S. Kinesthetic perception ia early blind adults. Research Bulletin o f the American Foundation for the Blind, 1973, 6, 175-191. 5. PANDOLE,K. B.. & CAIN,W. S. Constant effort during static and dynamic muscular exercise. Jownal o f Motor Behavior, 1974, 6 , 101-110. 6. ROHMERT, W. Physiologische Grundlagen der Erholungszeitbestimmung. Zentralleb l d t fur Arbeitswisrenschaft, 1965, 19, 1-28. 7. SIMONSON, E. (Ed.) Physiology of work capacity and fatigue. Springfield, IL: Thomas. 1971. Pp. 211-281. J. A., & TAYLOR, A. Fatigue of maintained voluntary muscle contraction 8. STEPHENS, in man. JournaL of Physiology, 1972, 220, 1-18. Accepted July 25, 1979.
Skills, 1979, 49, 475-479. @ Perceptual and Motor Skills 1979
MAINTENANCE OF UNCUED ISOMETRIC CONTRACTIONS BY BLIND AND SIGHTED CLAUDIA G . EMES
The U n i v e r ~ i t yo f Calgary Summa~y.-A comparison of 10 blind and 10 sighted subjects to a proprioceptive task was examined by analysis of response to maintenance o f uncued static contractions. In attempting to sustain hand-grip tensions at specified percentages of maximum voluntary contraction, blind and sighted groups showed no significant difference in performance.
Many rehabilitative techniques in mobiliry, activities of daily living and work, rest on the ability of blind persons to utilize perceptual information. Therefore, knowledge is required about perception and particularly kinesthetic perceptual development of blind individuals. Currently there is no evidence to support the notion that other senses may be heightened to compensate for loss of vision and in fact blind persons frequently demonstrate poor proprioceptive awareness (2, 4 ) . The present study was done to determine the relative performance of blind and noncued, sighted subjecrs on a proprioceptive task. Cain and Stevens ( 3 ) showed that, if subjects attempted to maintain a constant level of perceived work without visual cues, the isometric tension decreased with time. Abraham and Craig ( 1) in a similar study found the same results except where Cain and Stevens used pre-selected starting tensions, Abraham and Craig used a beginning tension which was a fixed percentage of each subject's maximum voluntary contraction. Abraham and Craig suggested that rhe subject's strength may affect the results of uncued tests, therefore the starting tension should be relative to the individual's strength. In the present investigation the question of whether sensory information from the hand played a role in performance was re-examined by comparing results from blind subjects and sighted subjects. This study compared ability to maintain an isometric tension without visual cues for specified periods of rime by both noncued, sighted and blind individuals.
METHOD Physiologists have demonstrated that, when subjects are required to maintain an isometric contraction at a constant level of perceived work without. visual cues, rhe isometric tension will decrease with time (1, 3 ) . It is suggested that the fast component of the tension decline is related to sensory adaptation involving the Golgi tendon organs. Since the Golgi tendon receptors provide proprioceptive information, this method was used to measure the awareness of blind individuals and sighted subjects. As in the work of Abraham and Craig ( I ) , subjects from this study were
476
C. G. EMES
asked to maintain an uncued isometric concraction at 70% maximum voluntary contraction for 30 sec.; 50%, 30% and 15% maximum voluntary contraction of their hand grip for 60 sec. These levels of perceived work were selected because Rohmert (6) found in a detailed study that 70% maximum voluntary concraction could be maintained for 30 sec., 50% for 60 sec., 30% for 2.5 min., and 15% for extended periods of time. The tension record and electromyographic (EMG) activity were recorded during each contraction. Equipment identical to that of Abraham and Craig was used. A hand grip dynamometer with a Wheatstone bridge circuit provided a conrinuous record of tension. The output of the bridge was amplified on a four-channel curvilinear recorder. The hand-grip section was bolted to the top of a table 33 in. high. A steel cable connected the pulling bar of the hand grip to a dynamomecer which was bolted to the floor. In line with the hand grip was a wooden trough in which the subject rested his elbow. The vertical support for the trough was moveable so for a subject seated at an appropriate height next to the table, the trough and vertical support ensured that the relationship of the forearm to the hand grip was constant while the arm was bent at 90" at the elbow. This method of stabilizing the body was effective for isolating the force developed by the forearm flexors ( 1 ) . Two surface electrodes were applied to the volar aspect of the arm over the flexor digitorurn sublimis. The first electrode was 2 cm. distal to the elbow and the intereleccrode distance was 5 cm. A ground electrode was placed midway between the vertebral borders of the scapulae. The EMG signal was rectified and integrated. A Narco PMP-4A model physiograph recorded the electrical activity. Ten blind subjects were selected from the male registry of the Canadian National Institute for the Blind. Five were institutional, five non-institutional and all were over 18 yr. of age. The cause of blindness varied among the subjects; however, all had been blind (less than 10% vision) since birth or within the first three years except for one subject who was blinded at 9 and the sighted group were 10 male college students. The test required performing static hand-grip contractions 1596, 30%, 50%, and 70% of maximum voluntary contraction without visual cues. For each experimental cension the subject repeated three trials. Each set of trials was tested on different days and the order of the tests varied randomly. For each test the subject was instructed to make a maximum voluncary contraction for 2 or 3 sec. The greatest cension of three trials was considered maximum. Rest intervals berween trials were 1 min. Once the maximum voluntary contraction was determined a 5-min. resr was imposed before testing of the percentage contractions began. The 5-min. rest intervals were adequate for complete recovery ( 7 ) .
477
UNCUED ISOMETRIC CONTRACTIONS
Each subject was then instructed to make the appropriate percentage (15, 30, 50 or 7 0 ) contraction of his maximum voluntary contraction and without visual cues, attempt to maintain his original starting tension. The 1596, 30%, and 50% tests lasted for 60 sec. while the 70% test lasted 30 sec.
RESULTS AND D~SCUSSION From Fig. 1 it is evident thac the decline in tension of uncued isometric contractions persisted for both the blind and the sighted groups. Very little difference exists between the groups at the 15 % maximum voluntary contraction. The curves for 30%, 50%, and 70% decline, suggesting that sighted subjects maintained a tension closes to the designated percent of maximum 100 90
SF 30
12
2% I0
* 70
I-"
B& 100 oa s'i a3 90 9 eo m
0
ZO
0
30
40
50
600
10
20
30
40
50
60
TIME IN SECONDS
FIG. 1. Decrease in tension at selected percentages of maximum voluntary contraction (MVC) in uncued tests
voluntary contraction; however, the differences were not significant. The differences between the means of the blind and rhe sighted subjects at the final second of sustained isometric contractions for 30%, 50%, and 70% measures are shown in Table 1. Both groups responded to the rest in the same manner as the uncued subjects of Abraham and Craig's ( 1) study. Without visual cues isometric tension can not be maintained. Other investigators (1, 3, 5 ) have questioned the contribution of fatigue to tension loss during uncued tests. Abraham and Craig (1) showed thac electrical activity, as monitored on the TABLE 1 MEANSOF BLINDAND SIGHTED SUBJECTS A T FINALSECOND OF SUSTAINED ISOMETRICCONTRACTIONS Group
n
M
Blind Sighted
9 10
30% (60 sec.) S D 6
75.3 77.1
31.8 10.8
0.38
50% (60 sec.) M S D t 74.5 82.6
15.8 13.4
1.15
70% (30 sec.) S D t
M
81.1 87.3
19.5 9.6
0.83
478
C. G. EMES
integrated EMG trace, decreased during uncued tests. Because an increase in electrical activity suggests muscle fatigue is occurring, a decrease in electrical activity suggests that a process other than fatigue is occurring ( 8 ) . In the present study fatigue was also studied using EMG traces and the blind and sighted subjects were compared on this factor.
FIG. 2. EMG record for uncued, isometric contraction at 30%, 50%, and 70% of maximum voluntary contraction
Fig. 2 shows that fatigue was probably not a significant factor only in the first 30 sec. of the 30% and 50% tests; however, the slope of the integrated EMG curve indicates that fatigue was involved in the tested response. At 50% of the maximum voluntary contraction sighted subjects showed a definite increase in electrical activity during the final 30 sec. of contraction while blind subjects showed a slight increase at the 30% level. These results do not differ from those of previous investigators ( 1, 3). EMG responses differed slightly between the two groups of this study which may be related to the small sample number (10 sighted, 10 blind) however other similar studies have used even smaller samples
(1,3,5). At the 70% level fatigue is believed to be dominating ( 1 , 3, 5 ) . The responses of the blind and sighted groups were not different. The two EMG
UNCUED ISOMETRIC CONTRACTIONS
479
readings at 15 and 30 sec. do not give a clear picture of a fatigue pattern. Generally the responses as demonstrated on a tension vs time plot plus an EMG trace show that blind subjects had no greater or less awareness of uncued isometric tension than sighted subjects. 1. ABRAHAM, W., &
REFERENCES CRAIG, A. B., JR Tension decline during isometric contractions
without visual cues. Medicine and Science i n Sports, 1975, 7, 99-104. 2. BARICK, H. P., FITTS,P. M., & SNETDBR,R. Reproduction of simple movements as a function of factors influencing proprioceptive feedback. Journal o f Experirnedal Psychology, 1955, 49, 445-454. 3. CAIN.W. S., & STEVENS, J. C Constant-effort contraction related to the electromyogram. Medicine and Science i n Sports, 1973, 5, 121-127. 4. LINDLEY,S. Kinesthetic perception ia early blind adults. Research Bulletin o f the American Foundation for the Blind, 1973, 6, 175-191. 5. PANDOLE,K. B.. & CAIN,W. S. Constant effort during static and dynamic muscular exercise. Jownal o f Motor Behavior, 1974, 6 , 101-110. 6. ROHMERT, W. Physiologische Grundlagen der Erholungszeitbestimmung. Zentralleb l d t fur Arbeitswisrenschaft, 1965, 19, 1-28. 7. SIMONSON, E. (Ed.) Physiology of work capacity and fatigue. Springfield, IL: Thomas. 1971. Pp. 211-281. J. A., & TAYLOR, A. Fatigue of maintained voluntary muscle contraction 8. STEPHENS, in man. JournaL of Physiology, 1972, 220, 1-18. Accepted July 25, 1979.
