Electromyographic analysis of the upper limb in healthy subjects for a postbreast cancer functional re-education perspective

In the breast cancer population, long-term musculoskeletal pathologies of the upper limb are common following oncological treatments. The soft and contractile tissues of the operated or irradiated area have numerous negative consequences (e.g., biomechanical alterations in the kinematics of the scapular-humeral rhythm, stiffening, weakness, and atrophy of the thoracic and shoulder muscles, etc.). These consequences lead to reduced passive and active mobility of the shoulder and a deficit in the strength of the entire upper limb. The goal of this investigation is to study, through healthy patients, selective exercises for the pectoralis major muscle with a view to functional re-education and to train shoulder stability. METHODS: Eight healthy women performed three types of upper limb exercises with elastic resistance (flexion, horizontal adduction, and “multi-plane” flexion-adduction-internal rotation). The muscles analyzed by surface electromyography (sEMG) were pectoralis major, latissimus dorsi, anterior deltoid, and upper trapezius. Assessment of maximum voluntary isometric contraction (MVIC) was performed before the tests to normalize the sEMG amplitude as MVIC percentage. The effect of the exercise type and its phase (concentric and eccentric) on the amplitude of muscle activation and co-activation was studied. RESULTS: The pectoralis major muscle reported significantly higher mean EMG activation amplitude (P<0.001) in the adduction exercise compared to the others. The exercises that present a higher mean co-activation index for the pectoralis major and latissimus dorsi pair (antagonists) are flexion and “multi-plane.” CONCLUSIONS: Exercises with elastic bands for horizontal adduction, anterior flexion, and internal rotation of the arm may contribute to the postrehabilitation phase to strengthen the pectoralis major, for greater co-activation and safe shoulder stability.