MUSCLE ACTIVATION DIFFERENCES BETWEEN ECCENTRIC AND CONCENTRIC ISOKINETIC EXERCISE

Purpose: The purpose of this study was to compare electromyographic (E MG) activity and joint moment of agonists and antagonists between isok inetic eccentric and concentric knee muscle actions. Methods: Twelve f emales (20.5 +/- 2.9 yr) performed maximum knee extension and flexion effort on a Biodex dynamometer isometrically and at concentric and ecc entric angular velocities ranging from 30 degrees.s(-1) to 150.s(-1). EMG activity of vastus lateralis, rectus femoris, vastus medialis, and hamstrings was also recorded. The moment and agonist EMG values were normalized as a percentage of the maximum isometric values. The antago nist EMG was normalized as a percentage of the IEMG activity of the sa me muscle group when acting as agonist at the same angular velocity an d angular position and taking into consideration the effects of muscle action. Results: Three-way ANOVA designs indicated significantly grea ter normalized eccentric moments compared with concentric moments (P < 0.05), whereas the eccentric normalized integrated EMG (IEMG) of agon ists and antagonists was significantly lower compared with the respect ive concentric IEMG values (P < 0.05). These differences were more evi dent at fast angular velocities. Conclusions: The present results demo nstrate that neural activation and the resulting muscular action are d ifferent between isokinetic eccentric and concentric tests and depend also on the angular velocity of the movement. The antagonist IEMG acti vity is different depending on the muscle examined. The IEMG activity of the antagonists in this study indicate that the antagonist activity is an important factor that affects the resultant joint moment during isolated isokinetic maximum voluntary joint movements.