Background: Individuals with scapular winging have a weak serratus anterior (SA) muscle, and to compensate, the pectoralis major (PM) and upper trapezius (UT) muscles excessively activate, which can cause upper extremity dysfunction. This study aimed to compare the effects of isometric horizontal abduction (IHA) on SA, PM, and UT muscle activity, as well as the SA/PM and SA/UT muscle activity ratios during knee push-up plus (KPP) at 90° and 120° of shoulder flexion. Objects: This study aimed to compare the effects of IHA on SA, PM, and UT muscle activity, as well as the SA/PM and SA/UT muscle activity ratios during KPP at 90° and 120° of shoulder flexion. Methods: This study, conducted at a university research laboratory, included 20 individuals with scapular winging. Participants performed KPP with and without IHA at 90° (KPP90) and 120° (KPP120) of shoulder flexion. SA, PM, and UT muscle activity were measured using surface electromyography. Results: PM activity in KPP90 with IHA was significantly lower than KPP90 and in KPP120 was significantly lower than KPP90. UT activity was significantly greater with IHA than without IHA and at 120° than 90° of shoulder flexion. SA/PM muscle activity ratio was significantly higher in KPP90 with IHA than without IHA and in KPP120 than in KPP90. SA/UT muscle activity ratio was significantly lower with IHA than without IHA. Conclusion: KPP90 with IHA and KPP120 are effective exercises to reduce PM activity and increase SA/PM muscle activity ratio. However, applying IHA in KPP90 also reduces SA/UT muscle activity ratio, implying that it would be preferable to apply KPP120 in individuals overusing their UT muscles.

Background: Shoulder horizontal abduction in the prone position (SHAP) has been reported as an effective exercise to strengthen the lower trapezius. However, the effects of pre-emptive scapular posterior tilt on scapular muscle activity and scapulohumeral movements during SHAP have not been examined. Objectives: To examine the effect of the addition of scapular posterior tilt on muscle activity of the trapezius and posterior deltoid, and scapular posterior tilt and shoulder horizontal abduction, during SHAP. Design: Cross-sectional study. Methods: Fifteen healthy male subjects performed two types of SHAP: general and modified SHAP (SHAP combined with pre-emptive scapular posterior tilt). To perform modified SHAP, pre-emptive scapular posterior tilt training was performed prior to the modified SHAP. Muscle activity of the middle and lower trapezius and posterior deltoid, and the amount of scapular posterior tilt and shoulder horizontal abduction, were measured during two types of SHAP. Results: Muscle activity of the lower trapezius and scapular posterior tilt was significantly increased during the modified SHAP, while muscle activity of the posterior deltoid and the amount of shoulder horizontal abduction were significantly decreased. However, the middle trapezius muscle activity did not change during the modified SHAP. Conclusion: The SHAP with pre-emptive scapular posterior tilt can be useful to strengthen the lower trapezius.