The normal relationship between fat and lean mass for mature (21-30 year old) physically fit men and women.

OBJECTIVE: Determine if relative body fat (%BF) remains a biological norm in physically active, non-obese American men and women and determine reference values for other components of body composition. METHODS: Participants (n = 174 men, 70 women) were physically fit U.S. Marine 2nd Lieutenants, in their third decade of physical maturity (age 21-30). Body composition was assessed by dual-energy x-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA); and body images were obtained by 3D body scans. RESULTS: For men and women, respectively, %BF averaged 16.2 ± 4.1 (median 15.3), 24.3 ± 4.5 (median 23.8); fat-free mass (FFM): 67.7 ± 7.2, 49.4 ± 5.3 kg; FFM index: 21.5 ± 1.8, 18.3 ± 1.6 kg/m2 ; and body mass index (BMI): 25.5 ± 1.9, 24.1 ± 2.2 kg/m2 . Bone mineral content (BMC) was 5% of FFM; total body water (TBW) was 70%-72% of FFM. Physique remained similar between median and higher percentiles of %BF. Only small changes in key measures were noted across the six-month training program. CONCLUSIONS: Mean %BF of healthy active men and women in 2021 remains very similar to the 15% and 25% posited in 1980, suggesting that relative body fat has a normal fat-lean relationship in physically mature humans. These data may bring new attention to sex-appropriate %BF.

Physical performance and body composition reference values for modern US Marine Corps women.

Women's roles in the US military have progressively changed over the past several decades. Previously women were barred from combat roles. Recent change in policy allow women into combat roles in the Marine Corps, and this has led to women being trained for combat specialties. Objectives: This observational cross-sectional study describes body composition and performance values for modern Marine Corps women. Methods: Volunteers were 736 Marine women who were assessed for body composition and physical performance; (age 29.5±7.3 (18-56) years; height 163.6±6.8 (131.0-186.1) cm; body mass 68.3±9.2 (42.0-105.3) kg; years in the military 8.9±6.8 (0.5-37) years-in-service). Body composition measures were obtained using dual-energy X-ray absorptiometry and single-frequency bioelectrical impedance analyses. Performance measures were obtained from official physical and combat fitness test scores (PFT; CFT) as well as from data on measured countermovement jumps (CMJ) on a calibrated force platform. Results: Mean body composition metrics for Marine women were: 47.5±5.7 fat free mass (FFM) (kg), 30.1%±6.4% body fat (%BF), 2.6±0.3 bone mineral content (kg), and 25.5±2.8 body mass index (kg/m2); performance metrics included 43.4±3.2 maximal oxygen uptake (VO2max; mL.kg.min), 22.4±7.1 CMJ height (cm) and 2575±565.2 CMJ peak power (W). Data showed strong correlations (r) (≥0.70) between PFT and VO2max scores (0.75), and moderate correlations (≥0.50) between CFT and VO2max scores (0.57), CFT and PFT scores (0.60), FFM and CMJ peak power (W) (0.68), and %BF to VO2max (-0.52), PFT (-0.54), CMJ-Ht (-0.52) and CMJ relative power (W/kg) (-0.54). Conclusion: Modern Marine women are both lean and physically high performing. Body composition is a poor predictor of general physical performance.

High precision but systematic offset in a standing bioelectrical impedance analysis (BIA) compared with dual-energy X-ray absorptiometry (DXA).

Bioelectrical impedance analysis (BIA) provides a practical method of body composition estimation for field research and weight management programmes, with devices and algorithms that have improved in recent years. We compared suitability of a commercial BIA system that uses multi-frequency-based proprietary algorithms (InBody 770, Cerritos, California, USA) and a laboratory-based validated single-frequency system (Quantum IV, RJL Systems, Clinton Township, Michigan, USA) with dual-energy X-ray absorptiometry (DXA) (iDXA, GE Lunar, Madison, Wisconsin, USA). Volunteers included fit non-obese active duty US Marines (480 men; 315 women), assessed by DXA and the two BIA systems. Both RJL and InBody BIA devices predicted DXA-based fat-free mass (FFM) (mean absolute error (MAE) 2.8 and 3.1 kg, respectively) and per cent body fat (%BF) (MAE 3.4% and 3.9%, respectively), with higher correlations from the InBody device (r2=0.96 (%BF) and 0.84 (FFM)) versus the RJL (r2=0.92 (%BF) and 0.72 (FFM)). InBody overpredicted FFM (bias +2.7, MAE 3.1 kg) and underpredicted %BF (bias -3.4 and MAE 3.9%) versus the RJL. A 3% correction factor applied to the InBody device results provided values very close to the DXA measurements. These findings support the application of modern BIA systems to body composition goals of maximum %BF and minimum lean body mass for both men and women.