Validity of Futrex-5000 for body composition determination

Area of Science:

• Human physiology
• Body composition analysis
• Sports science

Background:

• Accurate body fat assessment is crucial for health and performance monitoring.
• Traditional methods like underwater weighing (UWW) are accurate but impractical.
• Near-infrared interactance (NIR) devices like the Futrex-5000 (FTX) offer convenience but require validation.

Purpose of the Study:

• To compare the accuracy of skinfolds (SKF) and Futrex-5000 (FTX) for estimating body fat percentage.
• To validate these methods against the criterion standard of underwater weighing (UWW).
• To assess the influence of measurement sites and body mass index (BMI) on FTX accuracy.

Main Methods:

• 30 males and 31 females underwent body fat estimation using UWW, SKF (Y's Way to Fitness equations), and FTX (NIR at biceps plus additional sites).
• Correlation coefficients and percentage of subjects within +/- 4% of UWW values were calculated.
• Partial F-tests evaluated the predictive contribution of BMI and NIR measurements.

Main Results:

• SKF showed significantly higher correlations with UWW than FTX for males (0.95 vs 0.80), females (0.88 vs 0.63), and the total group (0.94 vs 0.81).
• 87% of subjects were within +/- 4% of UWW using SKF, compared to only 52% with FTX.
• FTX inaccurately estimated body fat at extremes (overestimating in lean, underestimating in obese); additional NIR sites did not improve accuracy. Using BMI improved FTX prediction in females.

Conclusions:

• Skinfolds (SKF) are a more accurate and reliable method for estimating body fat percentage compared to the Futrex-5000 (FTX).
• SKF provides better accuracy across the entire body fat continuum, particularly at the extremes.
• While NIR offers some predictive value, SKF remains superior for precise body composition assessment.