Effects of contralateral limb activity at different intensities and arousal on steadiness of knee extensor in young men and women

INTRODUCTION This study aimed to determine whether static muscle contraction in the contralateral limb at different intensities and arousal in response to an electric shock (ES) would affect the steadiness of ipsilateral knee extensors, and whether males would respond differently to females to these stressors. METHOD Ten males and ten females who were healthy and physically active, aged 19-33 years, gave their consent and participated in the study. Sitting in a test chair with each leg strapped to a load cell, subjects performed a series of unilateral and bilateral maximal and submaximal static voluntary knee extensions. The steadiness of the left leg, as indicated by the coefficient of variation (CV = Standard Deviation / Mean) of the torque production, was assessed when performing a 15-s contraction at 10, 30 or 50%MVC level, while the right leg performed a 10-s contraction at 10, 30 or 50%MVC which started 5 s after the left leg. An electric shock (10 pulses of 100-200mA, at 25Hz) was applied to the right knee 5 s into its contraction. Subjects were advised to focus on maintaining the left leg torque against the target level according to a visual feedback on computer screen. An analog scale was used to evaluate the level of arousal before and after each level of contraction and the ES. Repeated measures ANOVA with Bonferroni adjustment was used to evaluate the effects of the treatments. The experimental procedure was approved by the University Human Research Ethics Committee. RESULTS The statistical analysis detected significant interactions (P\u3c0.05) between left leg torque level, right leg torque level and electric shock on muscle steadiness. The post-hoc analysis showed that the CV of the left leg torque did not increase when the left leg muscle contracted alone, but was significantly affected by the right leg contraction at 30-50%MVC levels. The electric shock superimposed over the right leg contraction significantly elevated the arousal level, and affected the CV of the left leg particularly at 10%MVC, however did not induce additional impairment of muscles steadiness at higher contraction intensities. Similar patterns of response were found in the male and female subjects. DISCUSSION AND CONCLUSION It has been reported that the level of arousal affects the steadiness of hand muscles in a pinch task [1]. It is also known that contralateral activity affects ipsilateral performance. The present study further demonstrated that moderate levels of static knee extension in the contralateral limb would impair muscle steadiness (CV) of the ipsilateral limb in the precision task. The results also indicated that increased arousal level affected the steadiness of large muscle group, particularly at low level of static contraction. However, in general no significant difference was found between males and females in maintaining muscle steadiness at moderate levels of static knee extension