The relationship between body composition, lumbar strength, and lumbar flexibility in physiotherapy students

Lumbar fitness, which encompasses lumbar flexibility and strength, is a critical component of trunk stability and physical function among health sciences students, and body composition indicators may influence these characteristics. This study aimed to analyze the relationship between six body composition indicators (weight, body fat percentage, visceral fat, resting metabolic rate, body mass index, and body age) and lumbar flexibility and strength. A non-experimental correlational study was conducted involving 51 physiotherapy students. Body composition was measured using a bioelectrical impedance analyzer, lumbar flexibility using the Sit & Reach Test, and lumbar strength using a back dynamometer. Data were analyzed using Spearman’s rho because several variables were not normally distributed. Lumbar flexibility was significantly negatively correlated with weight (rs = -0.345, p = 0.013), whereas the other indicators showed no significant association (p > 0.05). Lumbar strength was significantly correlated with all six indicators (p < 0.05): resting metabolic rate (rs = 0.626, p < 0.001), weight (rs = 0.506, p < 0.001), visceral fat (rs = 0.486, p < 0.001), body age (rs = 0.333, p = 0.016), body mass index (rs = 0.309, p = 0.027), and body fat percentage (rs = -0.280, p = 0.047). Higher body weight was associated with lower lumbar flexibility, whereas higher resting metabolic rate, body weight, and visceral fat were associated with greater lumbar strength; in contrast, higher body fat percentage was associated with lower lumbar strength. These cross-sectional associations do not imply causality.