The effects of shoulder extension angle on elbow flexor hypertrophy in the cable curl exercise

This within-participant randomized study compared elbow flexor hypertrophy following cable curls performed in a neutral versus maximally extended shoulder position, with resistance profiles and elbow extension range of motion (ROM) matched between conditions. Thirty untrained men participated, with one arm assigned to train at the individualized peak shoulder extension angle and the contralateral arm at a neutral position. Twenty-four participants completed the intervention, which consisted of six to eight weekly sets of unilateral cable curls to momentary failure over 10 weeks under supervised conditions. Elbow flexor muscle thickness was assessed with ultrasonography at 50% and 70% of humerus length before and after the intervention. A Bayesian framework was used to estimate the average treatment effect (ATE) and quantify the strength of evidence with Bayes factors (BF). Both conditions produced increases in muscle thickness of approximately 7%-9%. Posterior distributions of the ATE were centered close to zero (Proximal/ATE_Neutral:Peak = -0.40 [95% CrI: -1.06 to 0.26 mm]; Distal/ATE_Neutral:Peak = 0.21 [95% CrI: -0.25-0.65 mm]), with BFs indicating anecdotal to moderate evidence in favor of the null hypothesis. These findings suggest that when resistance profiles, elbow ROM, and effort are matched, altering shoulder extension angle in isolation does not appear to produce meaningful differences in elbow flexor hypertrophy in untrained men over 10 weeks.