ABSTRACT

　The aim of this study is to compare motor unit discharge properties after exercise between concentric and eccentric contraction. Eighteen young healthy men performed repetitive concentric or eccentric isokinetic knee extension until they exerted less than 80% of the baseline strength. High-density surface electromyography was recorded during ramp-up isometric contraction to 50% of baseline strength and individual motor units were identified before and after the exercise. Motor units were tracked before and after the exercise. Muscle cross-sectional area evaluated by ultrasound and electrically evoked torque were measured. Sixty-four and fifty-three motor units were analyzed in concentric and eccentric conditions, respectively. Motor units recruited with moderate to high recruitments thresholds significantly decreased recruitment thresholds under both conditions. Motor unit discharge rate significantly increased after concentric contraction compared to eccentric contraction. A significant greater increase in muscle cross sectional area was noted under concentric condition. The evoked torque was significantly decreased under both conditions, but no difference between the conditions. These findings suggested that concentric contraction to failure contributes to greater neural input to muscle and metabolic responses than eccentric contraction.

DECENTE SPORTS SCIENCE Vol.44/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE