Partial Range, Full Gains? The Effect of 8 Weeks of Partial Range of Motion Training at Long Muscle Lengths on Elbow Flexor Hypertrophy and Strength in Trained Individuals.

We investigated the effects of initial partial range of motion (pROMinitial; 0°-70°) and full range of motion (fROM; 0°-140°) training on elbow flexor hypertrophy and strength in resistance-trained individuals. Thirteen individuals (males: n = 11, 26.6 ± 4.0 years, 89.2 ± 16.7 kg, and 183.3 ± 10.0 cm; females: n = 2, 24.0 ± 1.4 years, 75.5 ± 12.3 kg, and 168.0 ± 4.2 cm) completed a randomized within-subject study, performing unilateral preacher curls with each arm assigned to one condition over 8 weeks. Muscle thickness at 50% and 70% of the distance between the acromion and cubital fossa, maximal voluntary contraction (MVC) at elbow angles of 40° and 100°, and one-repetition maximum (1RM) were measured pre- and postintervention. Bayesian analyses were employed to infer effects from posterior distributions. Results showed similar improvements in muscle thickness at 50% humeral length between conditions, whereas pROMinitial exhibited trivial to small superiority at 70% elbow flexor length (standardized mean difference [SMD] = 0.10 and Bayes factor = 4.87). Additionally, MVC at 100° (SMD = 0.24 and Bayes factor = 3.02) and 1RM (SMD = 0.17 and Bayes factor = 1.95) demonstrated greater but negligible improvements with fROM, with weak to moderate evidence supporting the hypothesis of differential effectiveness across interventions. These findings suggest that pROMinitial may offer modest benefits for regional hypertrophy, particularly at longer muscle lengths. The results indicate that both training modalities can induce beneficial adaptations, with pROMinitial offering slight advantages in specific contexts. CLINICAL TRIAL REGISTRATION: This study was registered at German Clinical Trials Register with the registration number DRKS00035811.