STRENGTH AND ELECTROMYOGRAPHIC COMPARISON OF CONCENTRIC AND ECCENTRIC EXERCISE PERFORMED AT A CONSTANT ANGULAR VELOCITY 1408

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Isokinetic dynamometry has been used as a countermeasure for space flight-induced strength losses. Exercise countermeasures during space flight should result in maximal fatigue of motor units. Mean power frequencies (MPF) during maximal concentric and eccentric actions can determine which contractile mode serves as a greater stimulus. Space flight exercise should maximize work while maximally fatiguing motor units. Eight female volunteers gave written consent for participation. Concentric or eccentric-only training was performed on two days, separated by a minimum of 96 hours, with contractile mode randomized per subject. Volunteers performed 4 sets of 12 repetitions of elbow flexions at a velocity of 60 deg/s on a Lido isokinetic dynamometer (Loredan Inc., Davis, Ca) while MPF were obtained from their biceps brachii, brachioradialis, and palmaris longus using surface electromyography with the APAS system (Ariel Dynamics, Trabuco Canyon, Ca). MPF data were averaged during the first and last three repetitions of each workout. Rest periods were held constant at 60 seconds. Data were analyzed using a 2×2 (mode × time) ANOVA with significance established at the.05 level. Results indicate a mode effect for the brachioradialis, with a greater effect noted eccentrically (p=0.005). A significant correlation was noted for the brachioradialis, with a positive relationship between delta MPF scores and fatigue rates, suggesting the eccentric elbow flexions were a good countermeasure for that muscle. These data indicate an exercise countermeasure prescription for space flight should have an eccentric emphasis.