Cocontraction in the elbow and shoulder muscles during rapid cyclic movements in an aquatic environment.

The purpose of this study was to document the cocontraction patterns of the combined wrist-elbow-shoulder joint muscles during maximal-effort swimming. The subjects, nine high-performance athletes, swam 4 x 100 m at maximal effort with a 45 s rest after each 100 m run. Electromyographic (EMG) recording of six muscles was performed with surface electrodes and telemetry. The quality of the arm movement was verified with two video cameras and the movement was divided into four phases: the initial press, the inward scull, the outward scull and the air recovery. Eccentric work and antagonist co-activation of the arm extensors varied within the motion cycle but were mostly present during the inward scull; i.e. it is assumed that coactivation is transient movement and is phase-dependent despite the rapidity of the movement. These data suggest that both eccentric work and cocontractions are important features of rapid cyclic repetitive movement with the m. biceps and the m. brachioradialis as prime movers.