An isokinetic investigation of contractile mode's effect on the elbow flexors

Healthy, sedentary, college-age subjects (n = 16) performed concentric or eccentric maximal unilateral isokinetic (1.08 rad s(-1)) elbow flexor contractions (4 sets of 12 repetitions) to fatigue as physiological data were concurrently collected. Net caloric expenditure was determined using indirect calorimetry, whereas the electromyogram examined root mean square (RMS) and mean power frequency (MPF) values for the biceps brachii, brachioradialis, and palmaris longus. Eccentric exercise resulted in significantly greater (p < 0.05) absolute (total work per kilocalorie) and relative (total work per kilocalorie per kilogram) exercise efficiency values. Concentric biceps brachii and brachioradialis RMS values were significantly (p < 0.05) greater than corresponding eccentric values, suggesting greater motor unit recruitment. Concentric MPF values, a measure of motor unit fatigue, showed significantly (p < 0.05) greater before and after decrements following exercise for the biceps brachii and brachioradialis. Greater exercise efficiency with less motor unit recruitment and fatigue results from eccentric exercise.