## 4 Discussion
### Body Composition and Muscle Quality Differences  
Body composition is a critical factor influencing climbing performance [40], with studies using DXA showing that climbers generally have lower body fat percentages and increased lean muscle mass [35; 40; 41]. Indeed, recent findings suggest increased lean muscle mass in the forearm region among skilled climbers [42]. Nevertheless, we observed similar forearm muscle mass, muscle mass index, and anatomical metrics (e.g., ape index) between groups, consistent with findings in previous studies [1; 8]. Despite similar forearm muscle mass and anatomical metrics, lower body fat percentage facilitates greater force production relative to body weight in climbers [43]. This optimized body composition is critical in climbing, where excess mass increases metabolic cost [41; 44] and complicates the execution of complex movements and the maintenance of endurance during extended climbs [45]. Building on this, MQ emerges as a critical biomarker, offering insights into neuromuscular efficiency beyond traditional strength performance and neuromuscular metrics.  
MQ, defined as force per unit muscle mass [25; 30], reflects climbing-specific neuromuscular efficiency. In our study, climbers exhibited higher MQ in their finger flexors without increased muscle mass, indicating highly efficient force production. This efficiency aligns with the focus of elite climbers on functional adaptations (e.g., neural activation and muscle coordination) rather than hypertrophy [20]. Studies in other sports have shown that neural adaptations can compensate for lower muscle mass, emphasizing the relevance of MQ [25]. For example, comparing athletes with similar levels of MQ may help identify specific muscle mass or strength deficits, thereby guiding targeted interventions and optimizing training strategies. Moreover, MQ could serve as a sensitive monitoring tool to detect early declines in neuromuscular efficiency during periods of overtraining or insufficient recovery, helping to fine-tune training loads and reduce injury risk. Additionally, while MQ shows promise as a predictor of strength performance, further investigation is needed to determine its reliability in predicting climbing outcomes. These observations not only underscore the functional benefits of optimized MQ but also set the stage for exploring how training may moderate differences across sexes.  
Our analysis of sex differences in MQ revealed that non-climbers exhibit significant disparities between sexes. However, these differences are minimized among climbers. Consistent with this, cross-sectional studies have shown that arm MQ in females is consistently higher than in males across the lifespan [30; 31]. Although the precise mechanism remains unclear, evidence suggests that women maintain MQ better during aging [30; 31]. These differences may be explained by physiological factors influencing muscle efficiency, such as variations in fiber type predominance or selective neuromuscular activation [46]. In addition, previous studies have proposed mechanisms such as greater resistance to fatigue, enhanced mitochondrial efficiency, and estrogen-related protective effects on muscle tissue in females, which may contribute to relatively higher muscle quality despite lower muscle mass [47]. Nonetheless, this MQ disparity is not evident among climbers, indicating that training may mitigate such differences, thus positioning MQ as a sex-neutral metric for strength performance evaluation. This attenuation of sex-based differences in trained individuals likely reflects converging neuromuscular adaptations to climbing-specific demands, such as improved motor unit recruitment strategies and task-specific coordination patterns.