Stiffness and thickness of the upper trapezius muscle increase after repeated climbing bouts in male climbers

BACKGROUND: Indoor climbing involves overloading the shoulder girdle, including the rotator cuff and upper trapezius muscles. This on the field study aimed to investigate the effects of repeated climbing bouts on morphological and mechanical measures of the upper trapezius muscle. MATERIALS AND METHODS: Fifteen experienced male climbers participated in the study. Rate of perceived exertion (RPE), blood lactate concentration ([La(−)](b)), and stiffness and thickness over four points of the upper trapezius were assessed before and after a repeated climbing exercise. The procedure for the climbing exercise consisted of five climbs for a total time of 5-minutes per climb, followed by a 5-minute rest. RESULTS: The analysis showed an increase from baseline to after the 3rd climb (p ≤ 0.01) for RPE and after the 5th climb for [La(−)](b) (p ≤ 0.001). Muscle stiffness and thickness increased at all points (1–2–3–4) after the 5th climb (p ≤ 0.01). We found spatial heterogeneity in muscle stiffness and thickness; muscle stiffness was the highest at Point 4 (p ≤ 0.01), while muscle thickness reached the highest values at points 1–2 (both p ≤ 0.01). Moreover, the analysis between the dominant and non-dominant shoulder showed greater stiffness after the 1(st) climb at Point 1 (p = 0.004) and after the 5(th) climb at Point 4 (p ≤ 0.001). CONCLUSIONS: For muscle thickness, the analysis showed significant changes in time and location between the dominant and the non-dominant shoulder. Bilateral increases in upper trapezius muscle stiffness and thickness, with simultaneous increases in RPE and blood lactate in response to consecutive climbs eliciting fatigue.