Generalized bioelectric impedance-based equations underestimate body fluids in athletes

Area of Science:

• Sports Science
• Human Physiology
• Body Composition Analysis

Background:

• Accurate assessment of body fluids like total body water (TBW) and extracellular water (ECW) is crucial for athletic performance and health.
• Bioelectrical impedance analysis (BIA) is a common method for estimating body fluids, but its accuracy in athletes using generalized equations is debated.
• Validation against criterion methods like radioisotope dilution is essential to determine the reliability of BIA equations in specific populations.

Purpose of the Study:

• To externally validate athlete-specific and generalized predictive equations for TBW and ECW against radioisotope dilution in male and female athletes.
• To assess the agreement between specific and generalized BIA equations for estimating body fluids in a large cohort of athletes across various sports.

Main Methods:

• A large sample of 1371 athletes (921 men, 450 women) underwent BIA.
• TBW and ECW were measured using radioisotope dilution techniques in a subgroup of 185 athletes (132 men, 53 women) as the reference criterion.
• Two athlete-specific and eight generalized predictive equations were tested for their accuracy and agreement.

Main Results:

• Athlete-specific equations showed no significant bias and high accuracy (R² = 0.83–0.94) for estimating TBW and ECW compared to dilution methods.
• Most generalized equations significantly underestimated TBW and ECW (p < 0.05) with lower coefficients of determination (R² = 0.66–0.89).
• In the larger sample, generalized equations consistently yielded lower TBW and ECW values than athlete-specific equations, with few exceptions.

Conclusions:

• Athlete-specific BIA equations are validated for accurate estimation of TBW and ECW in male and female athletes.
• Generalized BIA equations lead to a significant underestimation of TBW and ECW in athletes, potentially impacting hydration status monitoring.
• The findings underscore the importance of using sport-specific predictive equations for reliable body fluid assessment in athletic populations.