Sex-based forearm morphology in climbers: an ultrasound study and it´s predictive value for climbing style

Background : Sport climbing is a physically demanding discipline that places repetitive mechanical load on the upper limbs, potentially leading to morphological adaptations or overuse injuries. Despite this, musculoskeletal ultrasound (USI) has been underutilized in climbing research. This study aims to investigate sex-related differences in forearm muscle and nerve morphology in climbers and to determine whether these structural features can predict climbing specialization (bouldering vs. sport climbing). Methods : A cross-sectional study was conducted with 50 recreational climbers (25 males, 25 females). Ultrasound imaging was used to assess the thickness of key forearm muscles (brachioradialis, pronator teres, flexor digitorum superficialis/profundus, pronator quadratus) and the median and radial nerves. Results: Significant sex differences were observed for all muscles and the median nerve (p < 0.001), with males exhibiting greater thickness. No differences were found for the radial nerve or between dominant and non-dominant limbs. Logistic regression identified flexor digitorum profundus (FDP) thickness as the strongest anatomical predictor of sport climbing, with each 1 mm increase in FDP thickness raising the odds of being a sport climber by 48.2%. The final model, including FDP, median nerve, and pronator teres thickness, showed excellent discriminative ability (AUC = 0.814, accuracy = 82%). Conclusions: Ultrasound-based assessments revealed robust sex-related morphological differences in climbers’ forearm musculature and median nerve. Greater FDP thickness is strongly associated with sport climbing specialization. These findings suggest that USI may be a valuable tool for profiling climbers, guiding training programs, and informing injury prevention strategies.