Whole Body Kinetic Chain Muscle Activity during selected Rehabilitation Exercises in Healthy and Injured Overhead Throwing Athletes.

Background: Overhead throwing athletes are susceptible to shoulder injuries as a result of breakdowns in kinetic chain (KC) sequencing. Progressive rehabilitation phases have been developed to aid return-to-play through increasing the demand and intensity on key structures. The Advanced Throwers Ten (ATT) is a well-established rehabilitation program within the advanced strengthening phase of rehabilitation designed to engage muscles across KC segments. Purpose: This study evaluated the activation levels of key muscles across KC segments in healthy and injured overhead throwing athletes during selected exercises within the ATT program. Study Design: Cross-Sectional Study. Methods: Thirty-three male overhead throwing athletes (17 healthy and 16 injured) were recruited from overhead sport teams and completed one set of selected exercises within the ATT program. Maximum Voluntary Contraction (MVC) was performed using manual muscle testing and calculated as the mean of two, five second efforts. Electromyography (EMG) was recorded for sixteen muscles, including: biceps brachii, deltoids (anterior, medial and posterior deltoids), trapezius (upper and lower), infraspinatus, pectoralis major, latissimus dorsi, serratus anterior, contralateral external oblique, gluteus maximus, biceps femoris, rectus femoris, lateral gastrocnemius (all surface electrodes) and supraspinatus (fine wire electrode). A three-way ANOVA determined main effects (group, exercise and muscle) and interactions. One-way ANOVAs determined muscle activity differences between exercises in both groups. Post-hoc independent t-tests were used to assessed mean muscle activity (%MVC) between groups for each exercise. Results: There were minimal differences in muscle activity levels between throwing groups, with low-to-moderate activities (< 40%MVC) recorded from muscles across most ATT exercises. Strengthening activity levels (> 40%MVC) were noted for posterior deltoid, lower trapezius and infraspinatus in injured throwers during exercises performed prone on a stability ball. Conclusion: Similar muscle activity levels were evident for healthy and injured overhead throwers during selected from the ATT program exercises, with limited strengthening activity levels apparent across the KC except during prone exercises. Level of Evidence: 3.