Scapular Muscle Activity in Overhead Athletes With Symptoms of Secondary Shoulder Impingement During Closed Chain Exercises

Abstract Tucker WS, Armstrong CW, Gribble PA, Timmons MK, Yeasting RA. Scapular muscle activity in overhead athletes with symptoms of secondary shoulder impingement during closed chain exercises. Objective To determine the amount of muscle activation in 4 scapular muscles in overhead athletes with and without a history of secondary shoulder impingement, during 3 upper extremity closed chain exercises. Design One-between (group), one-within (exercise) repeated measures. Setting Controlled laboratory study. Participants Overhead athletes (n=15; mean age ± SD, 21.0±2.5y; mean height ± SD, 176.0±7.8cm; mean weight ± SD, 76.1±13.4kg) demonstrating with symptoms of shoulder impingement and overhead athletes (n=15; mean age ± SD, 20.4±3.8y; mean height ± SD, 174.1±9.7cm; mean weight ± SD, 73.3±11.7kg) with no shoulder pathologies. Interventions Subjects completed 5 individual trials of a standard push-up, a push-up on an unstable surface, and a revolution on a shoulder rehabilitation device while electromyography (EMG) recorded muscle activity of the serratus anterior, upper trapezius, middle trapezius, and lower trapezius. Main Outcome Measures The mean EMG data for the 4 muscles from the standard push-up, push-up on an unstable surface, and shoulder rehabilitation device trials were normalized as a percentage of a maximum voluntary isometric contraction for each muscle. Results There was a statistically significant interaction for the middle trapezius (F2,56 =3.856; P =.027). The shoulder impingement push-up on an unstable surface (33.76%±26.45%) had significantly greater activation compared with the shoulder impingement standard push-up (25.88%±13.76%), the shoulder impingement shoulder rehabilitation device (9.40%±5.86%), and the nonpathology push-up on an unstable surface (19.49%±7.73%). The shoulder impingement standard push-up had significantly greater activation compared with the shoulder impingement shoulder rehabilitation device and nonpathology standard push-up (17.99%±7.31%). The nonpathology standard push-up and nonpathology push-up on an unstable surface had significantly greater activation compared with the nonpathology shoulder rehabilitation device (7.95%±4.30%). Conclusions These results suggest that the muscle activation of the middle trapezius differs in overhead athletes with a history of secondary shoulder impingement compared with those who lack this history during closed chain exercise, as well as within the 3 closed chain exercises. The l