INFLUENCES OF SEX AND LEVEL OF PERFORMANCE ON FREESTYLE STROKE - AN ELECTROMYOGRAPHY AND KINEMATIC STUDY

Surface Electromyography (EMG) of the upper arm was performed on 50 subjects (30 males and 20 females). The following six muscles were studied: M. flexor carpi ulnaris, M. brachioradialis, M. biceps brachii, M. triceps brachii and two parts of the M. deltoidus (anterior and medialis). A cinematographical analysis was synchronized with the EMG's recorded during swims at maximal speed. The kinematics data were: hip displacement, stroke rate and five stroke phases measured from the arm-trunk angles. EMG measurements were normalized for each subject and analysed using the statistical method of principal component analysis. The best swimmers, at the same relative effort, had a greater hip displacement, lower electrical muscular activity and more selective recruitement, indicating greater efficiency. The role of each muscle during the different phases was in agreement with previous investigations (2, 11, 13, 14, 19). The swimmer's technique, particularly the position of the upper arm during the push phase, influenced these results. Time parameters of the stroke were not significantly different for the various swimmers' levels. The conclusions were similar, for the females however, with a worse displacement of the hip.