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 (T _coupling) i.e., the duration of the isometric phase occurring between the stretch and the shortening of the muscle. However, instead of T _coupling, the contact time (T _contact)—i.e., the sum of T _coupling plus the duration of the stretching and shortening phases that precede and follow T _coupling—is more easily and often measured. The aim of this study was to investigate the T _coupling changes within a large range of T _contact, in order to propose a possible relationship between T _coupling and T _contact, thus allowing the accurate measurement of T _coupling only 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 T _contact (400, 700, 1,000, 1,500, 2,000 and 2,500 ms). The T _coupling and T _contact values were measured individually, from force platform recordings and the velocity of the carriage seat obtained by a tachometer. For the longest T _contact (i.e., from 850 to 2,500 ms), we observed a significant linear relationship between T _contact and T _coupling. This transition between T _contact shorter or longer than about 850 ms seems to be important and to correspond to T _coupling 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.