THE EFFECTS OF ANTAGONIST MOMENT ON THE RESULTANT KNEE-JOINT MOMENT DURING ISOKINETIC TESTING OF THE KNEE EXTENSORS

The purpose of this study was to examine the effects of moment of anta gonistic muscle on the resultant joint moment during isokinetic eccent ric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee extension and flexion efforts on a Biodex dynamometer at 0.52 rad . s(-1) (30 degrees . s(-1)). Electr omyographic (EMG) activity of vastus medialis and biceps femoris (hams trings) was also recorded. The antagonistic moment of the hamstrings w as determined by recording the integrated EMG (iEMG)/moment relationsh ip at different levels of muscle effort. The iEMG/moment curves were f itted using second-degree polynomials. The polynomials were then used to predict the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92 Nm and 28.97 Nm under concentric and eccentric conditions respectively; pair ed t-tests indicated that this was a significant difference (P < 0.05) . These results indicate that the resultant joint moment of knee exten sors is the result of both agonist and antagonist muscle activation. T he greater antagonist muscle activity under concentric activation cond itions may be partly responsible for the lower resultant joint concent ric moment of knee extensors compared with the corresponding eccentric activation. The antagonist moment significantly Effects comparisons b etween the isokinetic moments and agonist EMG and in vitro force measu rements under different testing (muscle action and angular velocity) c onditions.