Periscapular activity in subjects with scapular dyskinesis during push-ups on stable and unstable support surfaces

BACKGROUND: The scapular dyskinesis has been described as a sign of scapular instability due to weakness or imbalance of scapular muscles. OBJECTIVE: The aim of this study was to compare the EMG activity of the periscapular and abdominal muscles of asymptomatic subjects without and with scapular dyskinesis type II during a push-up exercise performed on different surface stability conditions. METHODS: Twenty-seven physically active men were allocated into two groups: the Control group (n = 14); and the Dyskinesis group (n = 13). All participants performed three variations of the push-up exercise: Stable, Push-up with hand instability, and Push-up with hand and feet instability. The EMG activity of serratus anterior, upper (UT), middle (MT) and lower (LT) trapezius, external oblique (EO) and rectus abdominis (RA) was recorded during each task. RESULTS: The control group showed an increase in MT activity (mean difference -3.46 to 8.66) under both instability conditions compared to stable push-ups (p < 0.001). The comparison between groups showed that the control group had higher MT activity (mean difference -10.07 to 13.82) compared to the dyskinesis group under unstable conditions (p < 0.012). CONCLUSION: The insertion of unstable surfaces increased MT activity in the control group only. The insertion of the unstable surface, either the hands or the footrest, did not provide significant effects for the other muscles.