Trapezius Muscle Activity During Bilateral Scapular Retraction With Shoulder External Rotation: Incorporation of Kinetic Chain and Surface

Abstract

Cobanoglu, G, Demirkan, MY, Ecemis, ZB, Karatas, N, and Guzel, NA. Trapezius muscle activity during bilateral scapular retraction with shoulder external rotation: Incorporation of kinetic chain and surface. J Strength Cond Res XX(X): 000–000, 2026—Incorporating trunk/lower limb movements and unstable surface exercises into shoulder rehabilitation may enhance kinetic chain engagement. The aim was to investigate the effect of incorporating the kinetic chain and unstable surface into Bilateral Scapular Retraction with Shoulder External Rotation (BSR-SER) exercise on trapezius muscle activation. Twenty asymptomatic subjects (10 female, 10 male, age = 24.5 ± 4.48 years, body mass index = 22.45 ± 3.06 kg·m ⁻² ) were included in the study. The BSR-SER was performed in standing, squat, and lunge positions on stable and unstable surfaces. Electromyographic activity of the upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) muscles was measured. The UT muscle activation in the squat position was lower on an unstable surface than on a stable surface ( p = 0.015). The MT muscle activation was higher in the squat position than in the lunge position ( p = 0.014). The LT muscle activation was significantly greater in the squat position than in both the standing ( p = 0.007) and lunge positions ( p = 0.016). Moreover, LT muscle activation was higher on the stable surface than on the unstable surface ( p = 0.040). Upper trapezius/MT ratio in the squat position was lower than in the standing ( p = 0.016) and lunge positions ( p = 0.012). The UT/LT ratio in squat position on unstable surface was lower than both standing ( p = 0.007) and lunge positions on an unstable surface ( p = 0.005). The squat position during BSR-SER exercise promotes higher activation of the MT and LT muscles compared with standing or lunge positions. Performing the squat position on an unstable surface may be the most suitable option for promoting trapezius muscle balance by reducing UT muscle activation and activation ratios. These findings suggest that integrating squat-based kinetic chain exercises into shoulder strengthening programs may be beneficial for optimizing trapezius muscle activation.