RECRUITMENT PATTERNS OF THE SCAPULAR ROTATOR MUSCLES IN FREESTYLE SWIMMERS WITH SUBACROMIAL IMPINGEMENT

Athletes with shoulder pathology consistently demonstrate abnormalitie s in scapular rotator activity, suggesting that muscle dysfunction is a factor to consider in the aetiology or recurrence of shoulder pain. However, one important measure of the coordinated activity between the scapular rotators, their timing or temporal recruitment pattern, rema ins undetermined. The purposes of this study were to 1. provide normat ive data on the temporal recruitment pattern of the scapular rotators in freestyle swimmers, 2. determine the effect of a unilateral shoulde r injury on this pattern, 3. determine whether these effects extend to the non-injured side, and 4. determine the effect of injury on the co nsistency (variability) of muscle recruitment. Surface EMG data for th e upper and lower trapezius and serratus anterior were recorded bilate rally from two groups of competitive freestyle swimmers during control led bilateral elevation in the plane of the scapula. An injured group comprising nine swimmers with unilateral shoulder pathology and a cont rol group of nine non-injured swimmers were included, Temporal data de termined for the onset of muscle activation for each muscle were then compared between groups using an ANOVA and a one-sided F test. The res ults of the study indicate that: in non-injured swimmers, upper trapez ius is activated 217 ms prior to shoulder motion, followed by serratus anterior activation 53 ms after motion commences. lower trapezius was not recruited until 349 ms after shoulder motion, when the arm had at tained 15 degrees elevation, In injured swimmers, all three muscles on the injured side displayed significantly increased variability in the timing of activation (p < 0.05), whilst the serratus anterior was sig nificantly delayed in its activation on the non-injured side (p < 0.05 ). Skill hand preference was shown to have no effect on muscle recruit ment, The findings of this study indicate that a relationship does exi st between shoulder injury and the temporal recruitment patterns of th e scapular rotators, such that injury reduces the consistency of muscl e recruitment. They further suggest that injured subjects have muscle function deficits on their unaffected side.