Abstract
Responses of single muscle fibers of human vastus lateralis to 8 weeks of either concentric or eccentric training were studied in 16 male subjects using a specially designed training machine with the compulsory rotation of pedals induced by electrical engine. The major difference of the machine from the traditional one was that the seat was not fixed firmly, but slid along an inclined beam. As a result, the lower extremities exerted the load which was a part of the subject's weight and depended on the angle of inclination. The machine was designed to choose either concentric or eccentric exercise of hip and knee extensors by changing the direction of pedal rotation. The aim of this experiment was to compare the effects of long-lasting training in concentric or eccentric regime with an equal external power. Fiber cross-sectional area (CSA), myonuclear number, myonuclear CSA, and myonuclear domain were analyzed in single muscle fibers. Myonuclear CSA and myonuclear number per mm of fiber length did not change after training in both regimes, although fiber CSA was increased significantly after eccentric training. Myonuclear domain size was also increased significantly by concentric and eccentric exercise. It was suggested that eccentric training was more effective for induction of hypertrophy of muscle fibers. However, these phenomena were not related to the increase of number and/or size of myonuclei. [J Physiol Sci. 2007;57 Suppl:S95]
