Scapulohumeral kinematics and neuromuscular control during scaption are associated with passive stiffness and strength of periscapular muscles in competitive adolescent swimmers

The passive stiffness and strength of periscapular muscles may affect scapulohumeral control, especially in overhead athletes due to sports-specific training. This study tried to assess the relationship between the passive stiffness and strength of periscapular muscles, scapulohumeral kinematics and neuromuscular control during scaption in swimmers. Ten male adolescent competitive front-crawl swimmers were recruited. The passive stiffness and strength of periscapular muscles were measured in standard postures by a hand-held myotonometer and dynamometer, respectively. Surface electromyography and electromagnetic tracking systems were synchronized to record the muscle activities and scapulohumeral kinematics during scaption. Correlations between the passive stiffness or strength of periscapular muscles and the kinematics or muscle activity were examined by Spearman's rank correlation coefficient. The maximal strength of periscapular muscles correlated positively with the ranges of upward and external rotation of the scapula and negatively with muscle activity during scaption. Passive stiffness of periscapular muscles was associated with the downward rotation of the scapula and triggered an increase in muscle activity. Increased passive stiffness or decreased strength in the periscapular muscles may affect their role in controlling the scapular rotation and contribute to compensation from adjacent muscles. Our findings suggest that when attempting to evaluate scapular behavior, it may be beneficial to examine muscle strength and passive stiffness of periscapular muscles.