CO ACTIVATION AND TENSION-REGULATING PHENOMENA DURING ISOKINETIC KNEEEXTENSION IN SEDENTARY AND HIGHLY SKILLED HUMANS

The aim of this study was to examine isokinetic torque produced by hig hly skilled (HS) and sedentary (S) human subjects, during knee extensi on, during maximal voluntary and superimposed electrical activation. T o verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), du ring maximal voluntary activation, their myo-electrical activities wer e detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric acti ons and isokinetic knee extensions at 14 angular velocities (from -120 to 300 degrees . s(-1)). The rms amplitude of each muscle was normali zed with respect to its rms amplitude when acting as agonist at 15 deg rees . s(-1). Whatever the angular velocity considered, peak torque an d constant angular torque at 65 degrees of HS were significantly highe r (P < 0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P < 0.05) than voluntary torque at - 120, - 90, - 60 and -30 degrees . s(-1) angular velocities. For a giv en velocity, the rms amplitude of VL and VM were significantly lower ( P < 0.05), during eccentric than during concentric actions, in S, but not in HS, However, whatever the angular velocity, ST co-activation in HS was significantly lower (P ( 0.05) than in S. We concluded that co -activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric actio n in S, support the possibility of the presence of a tension-regulatin g mechanism in sedentary subjects.