Multi-segment coordination: fatigue effects

Purpose: The aim of this study was to investigate the segmental coordinatio n of vertical jumps under fatigue. Methods: Twelve subjects performed maxim al countermovement jumps with and without fatigue, which was imposed by max imal continuous jumps in place until their maximal jump height corresponded to 70% of the nonfatigued condition. Video, ground reaction forces, and el ectromyographic signals were recorded to analyze the segmental coordination of countermovement jumps before (CMJ(1)) and after (CMJ(2)) fatigue. The m agnitude of joint extension initiation, peak joint angular velocity, and pe ak net power around the ankle, knee, and hip joints and their respective ti mes were determined. Results: CMJ(2) was characterized by a longer contact time, which was accompanied with an earlier movement initiation and several differences (P < 0.05) in the variables used to describe coordination. Whe n the movement duration was normalized with respect to the contact phase du ration, the differences between CMJ(1) and CMJ(2) were not sustained. A con sistent pattern was indicated, in which the segmental coordination did not differ between jump conditions. When the magnitude of the muscle activation was set aside, a remarkably consistent muscle activation time was noticed between conditions. Conclusions: It was indicated that countermovement jump s were performed with a consistent well-timed motion of the segments. A "co mmon drive," which acts without the knowledge of the muscle properties, was suggested as mediating and controlling the muscle activation timing betwee n agonist-antagonist muscle pairs.