Influence of the contact time on coupling time and a simple method to measure coupling time

Abstract

The enhancement of performance in stretch shortening cycle (SSC) exercises has been attributed to the recoil of elastic energy stored during the stretching phase and depends on the duration of the coupling time (Tcoupling) i.e., the duration of the isometric phase occurring between the stretch and the shortening of the muscle. However, instead of Tcoupling, the contact time (Tcontact) - i.e., the sum of Tcoupling plus the duration of the stretching and shortening phases that precede and follow Tcoupling - is more easily and often measured. The aim of this study was to investigate the Tcoupling changes within a large range of Tcontact, in order to propose a possible relationship between Tcoupling and Tcontact, thus allowing the accurate measurement of Tcouplingonly from a tachometer and force data obtained classically in vertical jumps, jumps on sledge apparatus and running on force treadmills. Eleven subjects performed SSC exercises on a sledge apparatus with a large range of Tcontact (400, 700, 1,000, 1,500, 2,000 and 2,500 ms). The Tcoupling and Tcontact values were measured individually, from force platform recordings and the velocity of the carriage seat obtained by a tachometer. For the longest Tcontact (i.e., from 850 to 2,500 ms), we observed a significant linear relationship between Tcontact and Tcoupling. This transition between Tcontact shorter or longer than about 850 ms seems to be important and to correspond to Tcoupling close to 300 ms. This limit observed in the present study could be explained physiologically due to a possible modification of the cross-bridges formation. © Springer-Verlag 2006.