Key body size/shape predictors of physical fitness in Saudi College-aged males: Role of the body roundness index

Physical fitness, a crucial factor in health and well-being, is influenced by an individual's body composition. This study aimed to identify the key body size/shape predictors of fitness test performances among university-level students with diverse weight categories. This cross-sectional study involved 495 healthy, recreationally active male university students aged 18-23 years, categorized into normal weight (NORMW, n = 256), overweight (OVERW; n = 156), and obese (OB; n = 124) groups based on their body mass index (BMI). Anthropometric measurements including weight, height, BMI, waist and hip circumference (WC and HC), waist-to-hip and waist-to-height ratios (WHR and WHtR), body roundness and shape body indexes (BRI and ABSI) were recorded. The shuttle-run, push-ups, 20m Multi-Stage shuttle-run, and sit-and-reach tests were performed. The OB and OVERW groups performed significantly lower fitness test performances than the NORMW group (medium-to-large effect size). The correlation matrix showed that all anthropometric measures correlated with test performances, except for the sit-and-reach in the OB group and the shuttle-run in the NORW group. Higher WHtR and HC improved shuttle-run performance predictability in the OB group (R2 = -0.29), while WC and HC, and WC and BMI improved push-up predictability in the OB (R2 = -0.38) and OVERW (R2 = -0.24) groups. BRI was the best indicator of VO2max performance, accounting for 56%, 42%, and 32% of its variance in OB, OVERW, and NORMW groups, respectively. The BRI is proposed as a potential alternative to BMI for evaluating cardiorespiratory endurance performance, enabling individual monitoring.