Effects of pretension on isometric force production

This study was designed to investigate the effect of muscle fiber distribution and pretension at various submaximal contraction levels on the isometric force-time curve during knee extension. Thirteen male physical education students volunteered as subjects. They were instructed to react to an auditory and light signal by extending their right knee as quickly and forcefully as possible. The contractions were performed from seven pretension levels ranging from 0% to 70% of maximal voluntary contraction value (MVC). The isometric force-time curves were analyzed for their maximal rate of isometric force production. Preliminary tension was found to have statistically significant, decreasing effects on isometric maximal strength produced from the pretension levels of 20%, 30%, and 40% of MVC and on the rate of isometric force production (RFD). Relatively, the decrease was greater for the RFD than for the maximal strength. The effect of the 20% preliminary tension on the RFD was greater (P less than 0.05) for subjects rich in fast-twitch muscle fibers in their m. vastus lateralis than for subjects rich in slow-twitch fibers. At the other preliminary tension levels, the intergroup differences did not reach the level of statistical significance.