ABSTRACT

　Physical performance is enhanced by counter movement. This phenomenon iscalled stretch-shortening cycle effect （SSC effect）．Recently, elasticity of attachedcross bridges and residual force enhancement （RFE） have been suggested as possiblemechanisms. This study examined the contribution of these factors by comparingthe SSC effect attained in fast and slow twitch fibers. Rabbit psoas（ fast） and soleus（slow） were harvested, and single muscle fibers were isolated. In the SSC trial, fiberswere isometrically activated at an average sarcomere length of 2.4 μm, and stretchedto 3.0 μm within 2 seconds. Immediately after the end of stretch, the fibers wereshortened to 2.4 μm within 2 seconds. In the control trial, fibers were isometricallyactivated at an average sarcomere length of 3.0 μm, and shortened to 2.4 μm in 2seconds. Mechanical work attained during the shortening phase was calculated, andrelative increase in mechanical work between SSC and control trials was adopted asthe index for the SSC effect. In addition, RFE and control trials were conducted. In the RFE trial, the fibers were isometrically activated at an average sarcomere length of2.4 μm, and then stretched to 3.0 μm within 2 seconds. After the end of stretch, fiberlength was kept constant for 15 seconds. In the control trial, fibers were isometricallyactivated at an average sarcomere length of 3.0 μm. This state was maintained for15 seconds. The isometric force of the RFE and control trials 15 seconds after theend of stretch was compared to confirm whether RFE was induced. SSC effect wassignificantly larger in the soleus than in the psoas, but the magnitude of RFE was notdifferent between the muscles. These results suggest that the observed difference in theSSC effect between the muscles was not caused by RFE, but by the elasticity of theattached cross bridges.

DECENTE SPORTS SCIENCE Vol.40/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE