Body Composition and Sleep Quality as Determinants of Combat Fitness in Army Personnel: Independent Contributions and Moderating Effects

Abstract Introduction Maintaining optimal body composition and sleep quality (SQ) is essential for preserving combat fitness in military personnel. However, whether body composition independently influences combat fitness components and whether SQ moderates the relationship between body composition and combat fitness remain unclear. Therefore, we examined these relationships to identify the main determinants of combat fitness. Materials and Methods This study recruited 92 elite army personnel, including company-grade officers and noncommissioned officers, who achieved the “Special Class” standard on the officially authorized army physical fitness test. Body composition was assessed by bioelectrical impedance analysis (BIA), and SQ was evaluated using the Pittsburgh sleep quality index (PSQI). Combat fitness was measured through 3 operationally relevant tasks: leg tuck (LT), 240-m shuttle run (SR), and combat performance test (CPT). Partial correlation was used to analyze the independent effects of body composition, although hierarchical regression examined the moderating role of SQ. Results Body fat percentage (BFP) showed significant correlations with LT (r = −0.58), SR (r = 0.51), and CPT (r = 0.44), whereas skeletal muscle mass (SMM) correlated with LT (r = 0.60), SR (r = −0.50), and CPT (r = −0.46). Moderation analysis revealed that lower SQ strengthened the negative effects of BFP on LT (R2 = 0.41) and SR (R2 = 0.39). In contrast, higher SQ enhanced the positive effect of SMM on CPT (R2 = 0.29). Conclusions These findings suggest that SQ can function as a moderating factor that either amplifies or mitigates the effect of body composition on combat fitness. Enhancing body composition—by reducing BFP and increasing SMM—and SQ should be considered concurrently to improve military combat performance.