This article was downloaded by: [Johann Christian Senckenberg] On: 01 September 2014, At: 00:21 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction a
TOMOMI SEKI & TATSUYUKI OHTSUKI
b
a
Physical Education Laboratory, Nara Saho Jogakuin Junior College , Rokuyaon-cho 806, Nara City, Nara, 630, Japan b
Laboratory of Human Movement, Faculty of Letters, Nara Women's University , Kitauoyanishimachi, Nara City, Nara, 630, Japan Published online: 24 Oct 2007.
To cite this article: TOMOMI SEKI & TATSUYUKI OHTSUKI (1990) Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction, Ergonomics, 33:9, 1131-1142, DOI: 10.1080/00140139008925318 To link to this article: http://dx.doi.org/10.1080/00140139008925318
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ERGONOMICS, 1990, VOL. 33, No.9, 1131-1142
Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction TOMOMI SEKI Physical Education Laboratory, Nara Saho Jogakuin Junior College, Rokuyaon-cho 806, Nara City, Nara, Japan 630
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
and T A TSUYUKI OHTSUKI Laboratory of Human Movement, Faculty of Letters, Nara Women's University, Kitauoya-nishimachi, Nara City, Nara, Japan 630
Keywords: Bilateral strength exertion; Isometric contraction; Voluntary strength; Submaximal strength. The influence of simultaneous bilateral exertion on muscle strength was tested under the conditions in which the same or different levelsof strength were exerted by the right and left arm (or hand). Isometric muscle strength of elbow flexion, elbow extension and hand grip was studied. Subjects voluntarily exerted 25%, 50% and 75% of maximal strength based on their subjective judgement without the feedback of the strength actually exerted. Involuntary decrements of muscle strength were caused by the bilateral exertion. Muscle strength of both sides decreased under the condition where the same levelof strength was exerted by the right and the left arm (or hand). When different levelsof strength were exerted by each arm (or hand), the strength of the weaker side considerably decreased, while the strength of the stronger side did not decrease.
1. Introduction For many everyday activities, we make movements using both hands: for example, cutting meat with a knife and fork; washing the face; hitting a ball with a bat, stick or club; and passing a basket-ball. Previous research has found that the performance of simultaneous bilateral movements with maximal effort was poorer than that of unilateral movements; that is muscle strength with maximal effort was smaller in bilateral exertion than in unilateral exertion (Henry and Smith 1961, Kroll 1965, Ohtsuki 1981a, 1983). It has also been reported that reaction time or movement time is greater in bilateral than in unilateral reaction time tasks (Corcos 1984, Kelso 1979, Ohtsuki 1981b). On the other hand, many of our movements in daily life or sports are performed with submaximal muscle strength and our movements are not always performed exerting the same muscle strength with the right arm as the left arm. Thus, the purpose of this experiment was to determine the influence of bilateral exertion on muscle strength when submaximal strength was required to be exerted. Special reference was made to the differences between the strength exerted by the right and the left limbs. 2.
Methods
2.J. Subjects (I) Elbow flexion: 13 right-handed adult females aged between 18 and 28 years (mean 18·8 years) served as subjects. 0014-0139/90 $3-00 © 1990 Taylor & Francis Ltd.
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T Seki and T Ohtsuki
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(2) Elbow extension: 22 right-handed adult females aged between 17 and 28 years (mean 17·5years) served as subjects, and 9 of them also participated in the elbow flexion experiment. (3) Grip strength: 21 right-handed adult females aged between 18 and 31 years (mean 20·2 years) served as subjects, one of whom also participated in the experiments of elbow flexion and extension. All subjects were volunteers and permission was readily obtained after explanation of the task of the experiment and time to be taken.
2.2. Apparatus (I) Elbow flexion: isometric muscle strength of elbow flexion was measured using the apparatus shown in figure I. Subjects sat with their eyes closed. They flexed both their elbows to 90°, and placed both upper arms on a table horizontally and parallel to each other. Their upper arms were fixed with bands to the upper arm holder. Subjects supinated their forearms until their palms faced backwards and made soft fists. They exerted isometric strength in the direction of elbow flexion by pulling on the wrist bands. Muscle strength was measured using a force transducer connected to the wrist bands (Ohtsuki 1983) and recorded by a direct read-out recorder (KYOWA RAPET RMS-IIMPT). (2) EI bow extension: the same apparatus was used, except that the chair and the table on which subjects placed their upper arms were turned round. Subjects sat on the chair, closed their eyes, and exerted isometric muscle strength in the direction of elbow extension. (3) Hand grip: the apparatus used is shown in figure 2. Subjects sat on a chair with eyes closed, and placed their forearms on a table. They gripped the two vertical cylindrical bars with each hand. One of the two bars was fixed and a part of the proximal phalanx of the thumb was pressed against this immovable bar. The other bar could be moved with little friction. The distance between the immovable bar and this movable bar was adjusted to the subject's hand size so that the middle phalanx of the other four digits were fitted to the movable bar.
Figure I. Apparatus for measurement of elbow flexion strength.
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
Simultaneous bilateral exertion and muscle strength
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Figure 2. Apparatus for measurement of hand grip strength. 2.3. Procedure The same procedure was employed in order to measure each of the three kinds of muscle strength as follows. First, subjects exerted isometric muscle strength with maximal effort with the right arm (or hand) alone, with the left arm (or hand) alone and with both arms (or hands) simultaneously. These three types of exertion of muscle strength were repeated once for each type to make one set. Each subject performed two sets. The order of the three types of exertion was randomized within a set. In unilateral muscle exertion, i.e.,right alone or left alone, the larger value of the two sets was adopted as the unilateral maximal muscle strength for right or left respectively. In bilateral exertion, right strength and left strength were summed, and the summed values of the first and second set were compared. Respective right strength and left strength of the set where the larger summed value was obtained were adopted as the strength of bilateral exertion with maximal effort. Next, the three different levels of muscle strength, i.e., 25%, 50% and 75% of unilateral maximal muscle strength were required to be exerted by the subject. No feedback of the strength actually exerted was given so that subjects had to decide the strength using their own subjective judgement. The speed of exertion of muscle strength was also determined by the subject, except that she had to finish each trial within 5 to lOs. In addition, subjects were instructed to increase muscle strength gradually until they judged that the strength had reached the required level and then to decrease muscle strength swiftly. Subjects exerted the three required levels of muscle strength unilaterally or bilaterally according to the 15 conditions shown in table 1. These 15 conditions can be categorized into three groups of conditions; U, BS and BO. 'U' is unilateral exertion, 'BS' is bilateral exertion of the same level of strength with right arm (or hand) as left arm (or hand) (i.e., bilateral same level condition) and 'BO' is bilateral exertion of the different levels of strength with right arm (or hand) from left arm (or hand) (i.e., bilateral
1134
T. Seki and T. Ohtsuki
Table I. U
BS BO
R2S, L2S, R2S=L2S, R2S L2S,
Experimental conditions. RSO, LSO, RSO=L50, R2S L2S,
R7S L7S R7S=L7S RSOL50
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
U: Unilateral condition. BS: Bilateral same level condition. BO: Bilateral different level condition. different level condition). For example, 'R25' categorized in 'U' indicates unilateral exertion of 25% of unilateral right maximal strength by the right arm (or hand). 'R50> U5' in 'BD' indicates simultaneous bilateral exertion of 50% of unilateral right maximal strength by the right arm (or hand) and 25% of unilateral left maximal strength by the left arm (or hand). Subjects first exerted muscle strength voluntarily according to the experimenter's specification of one of the 15 conditions and successively reproduced the muscle strength they had just exerted. The first exertion was based on the subjective judgement of the specified level of strength. In the present paper, only the data from the first exertion was used. The second exertion was based on the first strength regardless of whether the first strength exertion was subjectively judged as erroneous or not. This experimental paradigm was employed since we wanted to know how accurately the strength actually exerted on the basis of subjective judgement was reproduced. The difference between the first and the second strength was measured for the examination of accuracy of reproduction, which will be reported in a separate paper. These two successive muscle strength exertions constituted one trial. Five trials were performed in each of 15 conditions. Thus the 75 trials in toto were randomly ordered. The percentage of muscle strength actually exerted relative to the unilateral maximal muscle strength was calculated for the right and left arm (or hand), respectively. Mean values of five trials in each of I5 conditions were calculated for every subject, and treated as the individual value of the condition and used for the statistical analyses. 3.
Results
3.1. M aximal muscle strength (I) Elbow flexion: unilateral maximal muscle strength of the right arm of each subject ranged from 143N to 221N (mean ±s.d.: 170± 24N), and that of left arm ranged from 128N to 176N (I 53 ± 17N). During simultaneous bilateral exertion, the muscle strength with maximal effort decreased compared to that during unilateral exertion for both right and left arms. The percentage of the bilateral muscle strength with maximal effort relative to the unilateral maximal strength was 87·3 ± 6'6% (mean ±s.d.) for the right, and 92·1 ± 6·1% for the left. The difference in maximal strength between bilateral and unilateral exertion was statistically significant for both the right (t=6'94, df= 12, p0·05). (2) Elbow extension: unilateral maximal muscle strength of the right arm ranged from 64N to 137N (rnean j s.d.: 99±20N), and that of the left arm ranged from 67N to
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Simultaneous bilateral exertion and muscle strength
1135
129N (92 ± 18N). The percentage of the bilateral muscle strength with maximal effort was 94·3 ± 7·2% for the right, and 95·3 ± 5·5% for the left. The decrease of maximal strength by bilateral exertion from that by unilateral exertion was statistically significant for the right (t=3-89, df=21, p0·05). (3) Hand grip: unilateral maximal muscle strength of the right hand ranged from 243N to 520N (mean ± s.d.: 346 ± 67N), and that ofleft hand ranged from 159N to 415N (303 ± 65N). The percentage of the bilateral muscle strength with maximal effort was 97·9 ± 6·8% for the right, and 98·0 ± 9·1% for the left. The strength with maximal effort by bilateral exertion showed a tendency to decrease as compared to that by unilateral exertion for either right or left, although these decreases were not statistically significant (right: t= 1·42, df=20, p>0·05; left: t= 1·03, df=20, p>0·05). 3.2. Submaximal muscle strength Figures 3 to 5 show the mean values of muscle strength exerted under each condition of table I. All kinds of exertions of muscle strength, i.e.,elbow flexion, elbow extension and hand grip, showed the same tendency. The muscle strength exerted in the bilateral same level condition (BS) was significantly smaller than that in the unilateral condition (V) for all three levels, 25%,50% and 75%. Table 2 shows the differences in muscle strength between conditions BS and V (8S-V) and the results of statistical treatment. In the case of bilateral different level condition (BO), the strength of the stronger side ('" and t:" in figures 3 to 5) approximated to the unilateral strength (. and 0). On the other hand, the strength of the weaker side (. and 0) decreased remarkably as compared to the strength in condition V. Furthermore, the strength of the weaker side in condition BO was smaller than that in condition BS. Table 3 summarizes the differences between the strength in condition BO and that in V (BO-V). Table 4 shows the differences between the strength of the weaker side in condition BO and the strength in condition BS (BO-BS). eo
U
RL
•
eo
BS(R=L).D
o
BD(R>U. i) BD(RLJ" 0 BO(R
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction a
TOMOMI SEKI & TATSUYUKI OHTSUKI
b
a
Physical Education Laboratory, Nara Saho Jogakuin Junior College , Rokuyaon-cho 806, Nara City, Nara, 630, Japan b
Laboratory of Human Movement, Faculty of Letters, Nara Women's University , Kitauoyanishimachi, Nara City, Nara, 630, Japan Published online: 24 Oct 2007.
To cite this article: TOMOMI SEKI & TATSUYUKI OHTSUKI (1990) Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction, Ergonomics, 33:9, 1131-1142, DOI: 10.1080/00140139008925318 To link to this article: http://dx.doi.org/10.1080/00140139008925318
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ERGONOMICS, 1990, VOL. 33, No.9, 1131-1142
Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction TOMOMI SEKI Physical Education Laboratory, Nara Saho Jogakuin Junior College, Rokuyaon-cho 806, Nara City, Nara, Japan 630
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
and T A TSUYUKI OHTSUKI Laboratory of Human Movement, Faculty of Letters, Nara Women's University, Kitauoya-nishimachi, Nara City, Nara, Japan 630
Keywords: Bilateral strength exertion; Isometric contraction; Voluntary strength; Submaximal strength. The influence of simultaneous bilateral exertion on muscle strength was tested under the conditions in which the same or different levelsof strength were exerted by the right and left arm (or hand). Isometric muscle strength of elbow flexion, elbow extension and hand grip was studied. Subjects voluntarily exerted 25%, 50% and 75% of maximal strength based on their subjective judgement without the feedback of the strength actually exerted. Involuntary decrements of muscle strength were caused by the bilateral exertion. Muscle strength of both sides decreased under the condition where the same levelof strength was exerted by the right and the left arm (or hand). When different levelsof strength were exerted by each arm (or hand), the strength of the weaker side considerably decreased, while the strength of the stronger side did not decrease.
1. Introduction For many everyday activities, we make movements using both hands: for example, cutting meat with a knife and fork; washing the face; hitting a ball with a bat, stick or club; and passing a basket-ball. Previous research has found that the performance of simultaneous bilateral movements with maximal effort was poorer than that of unilateral movements; that is muscle strength with maximal effort was smaller in bilateral exertion than in unilateral exertion (Henry and Smith 1961, Kroll 1965, Ohtsuki 1981a, 1983). It has also been reported that reaction time or movement time is greater in bilateral than in unilateral reaction time tasks (Corcos 1984, Kelso 1979, Ohtsuki 1981b). On the other hand, many of our movements in daily life or sports are performed with submaximal muscle strength and our movements are not always performed exerting the same muscle strength with the right arm as the left arm. Thus, the purpose of this experiment was to determine the influence of bilateral exertion on muscle strength when submaximal strength was required to be exerted. Special reference was made to the differences between the strength exerted by the right and the left limbs. 2.
Methods
2.J. Subjects (I) Elbow flexion: 13 right-handed adult females aged between 18 and 28 years (mean 18·8 years) served as subjects. 0014-0139/90 $3-00 © 1990 Taylor & Francis Ltd.
1132
T Seki and T Ohtsuki
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
(2) Elbow extension: 22 right-handed adult females aged between 17 and 28 years (mean 17·5years) served as subjects, and 9 of them also participated in the elbow flexion experiment. (3) Grip strength: 21 right-handed adult females aged between 18 and 31 years (mean 20·2 years) served as subjects, one of whom also participated in the experiments of elbow flexion and extension. All subjects were volunteers and permission was readily obtained after explanation of the task of the experiment and time to be taken.
2.2. Apparatus (I) Elbow flexion: isometric muscle strength of elbow flexion was measured using the apparatus shown in figure I. Subjects sat with their eyes closed. They flexed both their elbows to 90°, and placed both upper arms on a table horizontally and parallel to each other. Their upper arms were fixed with bands to the upper arm holder. Subjects supinated their forearms until their palms faced backwards and made soft fists. They exerted isometric strength in the direction of elbow flexion by pulling on the wrist bands. Muscle strength was measured using a force transducer connected to the wrist bands (Ohtsuki 1983) and recorded by a direct read-out recorder (KYOWA RAPET RMS-IIMPT). (2) EI bow extension: the same apparatus was used, except that the chair and the table on which subjects placed their upper arms were turned round. Subjects sat on the chair, closed their eyes, and exerted isometric muscle strength in the direction of elbow extension. (3) Hand grip: the apparatus used is shown in figure 2. Subjects sat on a chair with eyes closed, and placed their forearms on a table. They gripped the two vertical cylindrical bars with each hand. One of the two bars was fixed and a part of the proximal phalanx of the thumb was pressed against this immovable bar. The other bar could be moved with little friction. The distance between the immovable bar and this movable bar was adjusted to the subject's hand size so that the middle phalanx of the other four digits were fitted to the movable bar.
Figure I. Apparatus for measurement of elbow flexion strength.
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
Simultaneous bilateral exertion and muscle strength
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Figure 2. Apparatus for measurement of hand grip strength. 2.3. Procedure The same procedure was employed in order to measure each of the three kinds of muscle strength as follows. First, subjects exerted isometric muscle strength with maximal effort with the right arm (or hand) alone, with the left arm (or hand) alone and with both arms (or hands) simultaneously. These three types of exertion of muscle strength were repeated once for each type to make one set. Each subject performed two sets. The order of the three types of exertion was randomized within a set. In unilateral muscle exertion, i.e.,right alone or left alone, the larger value of the two sets was adopted as the unilateral maximal muscle strength for right or left respectively. In bilateral exertion, right strength and left strength were summed, and the summed values of the first and second set were compared. Respective right strength and left strength of the set where the larger summed value was obtained were adopted as the strength of bilateral exertion with maximal effort. Next, the three different levels of muscle strength, i.e., 25%, 50% and 75% of unilateral maximal muscle strength were required to be exerted by the subject. No feedback of the strength actually exerted was given so that subjects had to decide the strength using their own subjective judgement. The speed of exertion of muscle strength was also determined by the subject, except that she had to finish each trial within 5 to lOs. In addition, subjects were instructed to increase muscle strength gradually until they judged that the strength had reached the required level and then to decrease muscle strength swiftly. Subjects exerted the three required levels of muscle strength unilaterally or bilaterally according to the 15 conditions shown in table 1. These 15 conditions can be categorized into three groups of conditions; U, BS and BO. 'U' is unilateral exertion, 'BS' is bilateral exertion of the same level of strength with right arm (or hand) as left arm (or hand) (i.e., bilateral same level condition) and 'BO' is bilateral exertion of the different levels of strength with right arm (or hand) from left arm (or hand) (i.e., bilateral
1134
T. Seki and T. Ohtsuki
Table I. U
BS BO
R2S, L2S, R2S=L2S, R2S L2S,
Experimental conditions. RSO, LSO, RSO=L50, R2S L2S,
R7S L7S R7S=L7S RSOL50
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
U: Unilateral condition. BS: Bilateral same level condition. BO: Bilateral different level condition. different level condition). For example, 'R25' categorized in 'U' indicates unilateral exertion of 25% of unilateral right maximal strength by the right arm (or hand). 'R50> U5' in 'BD' indicates simultaneous bilateral exertion of 50% of unilateral right maximal strength by the right arm (or hand) and 25% of unilateral left maximal strength by the left arm (or hand). Subjects first exerted muscle strength voluntarily according to the experimenter's specification of one of the 15 conditions and successively reproduced the muscle strength they had just exerted. The first exertion was based on the subjective judgement of the specified level of strength. In the present paper, only the data from the first exertion was used. The second exertion was based on the first strength regardless of whether the first strength exertion was subjectively judged as erroneous or not. This experimental paradigm was employed since we wanted to know how accurately the strength actually exerted on the basis of subjective judgement was reproduced. The difference between the first and the second strength was measured for the examination of accuracy of reproduction, which will be reported in a separate paper. These two successive muscle strength exertions constituted one trial. Five trials were performed in each of 15 conditions. Thus the 75 trials in toto were randomly ordered. The percentage of muscle strength actually exerted relative to the unilateral maximal muscle strength was calculated for the right and left arm (or hand), respectively. Mean values of five trials in each of I5 conditions were calculated for every subject, and treated as the individual value of the condition and used for the statistical analyses. 3.
Results
3.1. M aximal muscle strength (I) Elbow flexion: unilateral maximal muscle strength of the right arm of each subject ranged from 143N to 221N (mean ±s.d.: 170± 24N), and that of left arm ranged from 128N to 176N (I 53 ± 17N). During simultaneous bilateral exertion, the muscle strength with maximal effort decreased compared to that during unilateral exertion for both right and left arms. The percentage of the bilateral muscle strength with maximal effort relative to the unilateral maximal strength was 87·3 ± 6'6% (mean ±s.d.) for the right, and 92·1 ± 6·1% for the left. The difference in maximal strength between bilateral and unilateral exertion was statistically significant for both the right (t=6'94, df= 12, p0·05). (2) Elbow extension: unilateral maximal muscle strength of the right arm ranged from 64N to 137N (rnean j s.d.: 99±20N), and that of the left arm ranged from 67N to
Downloaded by [Johann Christian Senckenberg] at 00:21 01 September 2014
Simultaneous bilateral exertion and muscle strength
1135
129N (92 ± 18N). The percentage of the bilateral muscle strength with maximal effort was 94·3 ± 7·2% for the right, and 95·3 ± 5·5% for the left. The decrease of maximal strength by bilateral exertion from that by unilateral exertion was statistically significant for the right (t=3-89, df=21, p0·05). (3) Hand grip: unilateral maximal muscle strength of the right hand ranged from 243N to 520N (mean ± s.d.: 346 ± 67N), and that ofleft hand ranged from 159N to 415N (303 ± 65N). The percentage of the bilateral muscle strength with maximal effort was 97·9 ± 6·8% for the right, and 98·0 ± 9·1% for the left. The strength with maximal effort by bilateral exertion showed a tendency to decrease as compared to that by unilateral exertion for either right or left, although these decreases were not statistically significant (right: t= 1·42, df=20, p>0·05; left: t= 1·03, df=20, p>0·05). 3.2. Submaximal muscle strength Figures 3 to 5 show the mean values of muscle strength exerted under each condition of table I. All kinds of exertions of muscle strength, i.e.,elbow flexion, elbow extension and hand grip, showed the same tendency. The muscle strength exerted in the bilateral same level condition (BS) was significantly smaller than that in the unilateral condition (V) for all three levels, 25%,50% and 75%. Table 2 shows the differences in muscle strength between conditions BS and V (8S-V) and the results of statistical treatment. In the case of bilateral different level condition (BO), the strength of the stronger side ('" and t:" in figures 3 to 5) approximated to the unilateral strength (. and 0). On the other hand, the strength of the weaker side (. and 0) decreased remarkably as compared to the strength in condition V. Furthermore, the strength of the weaker side in condition BO was smaller than that in condition BS. Table 3 summarizes the differences between the strength in condition BO and that in V (BO-V). Table 4 shows the differences between the strength of the weaker side in condition BO and the strength in condition BS (BO-BS). eo
U
RL
•
eo
BS(R=L).D
o
BD(R>U. i) BD(RLJ" 0 BO(R
