THE ACUTE EFFECTS OF PASSIVE STRETCHING ON ACTIVE MUSCULOTENDINOUS STIFFNESS1594

Abstract

It has been established that acute muscle stretching is an effective means of reducing passive joint stiffness while increasing joint range of motion(JROM). Although a clear understanding of the mechanisms responsible for these effects remains elusive, it is commonly reported that passive stretching reduces the stiffness of the connective tissue structures crossing the joint, including muscle and tendon. If musculotendinous stiffness does decrease after passive stretching, then it is possible that stretching might also reduce the stiffness of the series elastic component, as described by A. V. Hill's (1938) classical muscle model. In turn, this might influence the storage of elastic energy during stretch-shortening movements. The purpose of this study, therefore, was to establish the effect of an acute bout of passive stretching on musculotendinous stiffness under active conditions (active stiffness). Ten male subjects (age: 24.9 ± 5.3 yrs) performed a modified version of a non-invasive technique designed by Cavagna (J. Appl. Physiol., 1970), to measure the active stiffness of the triceps surae muscle-tendon complex. Stiffness measures were taken before and after passively stretching the triceps surae muscle group. Ankle JROM was also measured before and after the stretching bout. Although ankle JROM increased significantly (from 29.3± 3.3° to 31.3 ± 3.2°; p < 0.01) as a result of the stretching procedure, active stiffness remained unchanged (28.7 ± 4.9 kN/m vs 28.4 ± 4.8 kN/m; p > 0.05). Therefore, while acute muscle stretching may reduce passive joint stiffness, stretching does not appear to alter the active stiffness of the musculotendinous unit. Consequently, it is unlikely that acute stretching exercises influence the storage of elastic energy in skills which take advantage of the stretch-shortening phenomenon.