Effects of contraction intensity, contralateral limb activity and electric shock on steadiness of knee extensor
Zhou, S, Hu, H, Goldenberg, R & Shield, A, 'Effects of contraction intensity, contralateral limb activity and electric shock on steadiness of knee extensor', Proceedings 2003 Australian Conference of Science and Medicine in Sport: Tackling the barriers to participation and performance: Journal of Science and Medicine in Sport, vol. 6, no. 4, supplement 1, p. 21, Canberra, ACT, 25-28 October.
The study aimed to determine the effects of inter-limb interaction, contraction intensity and arousal on the steadiness in force production of knee extensors. Ten healthy men, mean age 25.4yrs (range 20-33), gave their consent and participated in the study. Sitting in a test chair with each leg strapped to a load cell, subject performed a series of unilateral and bilateral maximal and submaximal voluntary knee extensions. The steadiness of the left leg, as indicated by coefficient of variation of torque, was assessed when performing a 15s isometric contraction at 10, 30, or 50%MVC level, while the right leg performed a 10s contraction at 10, 30, or 50%MVC which started 5s after the left leg. An electric shock (10 pulses of 100-200mA, at 25Hz) was applied to the right leg 5s into its contraction. Subject was advised to focus on the left leg steadiness according to a visual feedback on computer screen. Repeated measures ANOVA with Bonferroni adjustment detected significant effects (P<0.05) of left leg and right leg contraction intensities, and electric shock on muscle steadiness. The left leg steadiness was impaired when the torque increased to 50%MVC, and when the right leg started contraction. The electric shock affected steadiness at lower contraction intensities but did not induce additional reduction of steadiness at 50%MVC level, while the cognitive arousal level was significantly elevated after receiving the shock. It is concluded that contraction intensity, contralateral limb activity and arousal affect muscle steadiness in a precision task during submaximal isometric knee extension.