Shoulder Complex Dysfunction Through an Evolutionary Lens: The Need for Closed Kinetic Chain Loading in Upper Extremity Program Design.

This review examines rotator cuff and shoulder complex dysfunction through an evolutionary framework and aims to translate these concepts into practical resistance training applications for strength and conditioning and rehabilitation professionals. Comparative anatomy and functional biomechanics of the human and non-human primate shoulder complexes are reviewed to illustrate how evolutionary pressures shaped an upper extremity system optimized for stability and force transmission under closed kinetic chain (CKC) loads. In contrast, many contemporary resistance training practices emphasize high-load, open kinetic chain (OKC) exercises that may impose elevated soft tissue strain and shear forces while potentially diminishing the engagement of the scapulothoracic and trunk stabilization mechanisms evolved to protect the shoulder complex. This proposed evolutionary mismatch may contribute to the high prevalence of shoulder dysfunction observed in the modern human population. Rotator cuff pathology arises through a combination of mechanisms, including, but not limited to, age-related tendon degradation, anatomical variations, mechanical overload factors, as well as systemic comorbidities. The contribution of habitual loading patterns to this multifactorial etiology has been considered in the literature, but this review advances a novel evolutionary mismatch hypothesis as one framework through which a primary biomechanical cause of overuse shoulder pathology may be examined. Applications of these concepts to exercise program design are presented. Specifically, training modifications consider moderately loaded CKC exercises performed at higher volumes with an emphasis on movement velocity and power generation. Incorporating moderate-load, high-volume, high-velocity CKC exercises may preserve rotator cuff integrity and optimize upper extremity function across the lifespan while potentially reducing the loading demands and associated mechanical stress that, under high-load or high-volume conditions, traditional OKC training models place on the shoulder and therefore, challenge the shoulder's evolved structural tolerance.