Generalized bioelectric impedance‐based equations underestimate body fluids in athletes

Abstract

The current study aimed: (i) to external validate total body water (TBW) and extracellular water (ECW) derived from athlete and non‐athlete predictive equations using radioisotope dilution techniques as a reference criterion in male and female athletes; (ii) in a larger sample, to determine the agreement between specific and generalized equations when estimating body fluids in male and female athletes practicing different sports. A total of 1371 athletes (men: n = 921, age 23.9 ± 1.4 y; women: n = 450, age 27.3 ± 6.8 y) participated in this study. All athletes underwent bioelectrical impedance analyses, while TBW and ECW were assessed with dilution techniques in a subgroup of 185 participants (men: n = 132, age 21.7 ± 5.1 y; women: n = 53, age 20.3 ± 4.5 y). Two specific and eight generalized predictive equations were tested. Compared to the criterion methods, no mean bias was observed using the athlete‐specific equations for TBW and ECW (−0.32 to 0.05, p > 0.05) and the coefficient of determination ranged from R2 = 0.83 to 0.94. The majority of the generalized predictive equations underestimated TBW and ECW (p < 0.05); R2 ranged from 0.66 to 0.89. In the larger sample, all the generalized equations showed lower TBW and ECW values (ranging from −6.58 to −0.19, p < 0.05) than specific predictive equations; except for TBW in female power/velocity (one equation) athletes and team sport (two equations). The use of generalized BIA‐based equations leads to an underestimation of TBW, and ECW compared to athlete‐specific predictive equations. Additionally, the larger sample indicates that generalized equations overall provided lower TBW and ECW compared to the athlete‐specific equations.

Reference Percentiles for Bioelectrical Phase Angle in Athletes

“…Body mass index (BMI) was calculated as total body mass (kilograms) divided by height (meters) squared. BIA was performed according with standardized procedures specific for athletes [ 9 ]. The bioelectrical phase angle was directly measured with BIA (BIA 101, Akern, Florence, Italy), which applies an alternating current of 800 μA at a single frequency of 50 kHz.…”

“…Due to the portability and ease of application, the use of the bioelectrical impedance analysis (BIA) has been increasing in sports practice especially because current studies have revealed that when following standardized protocols for BIA assessment, body composition measurements are comparable to more sophisticated clinical methods [ 7 , 8 , 9 , 10 ]. In addition, BIA yields additional raw bioelectrical parameters that can be independently used to qualitatively track body composition [ 7 , 8 ].…”

Effects of the COVID-19 Lockdown on Body Composition and Bioelectrical Phase Angle in Serie A Soccer Players: A Comparison of Two Consecutive Seasons

“…Among the methods for assessing body composition, bioelectrical impedance analysis (BIA) has recently gained relevance, especially in soccer [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ], where field and user-friendly methods are warranted [ 16 ]. Through the measurement and use of bioelectrical resistance (R) and reactance (Xc) in predictive equations, quantification of a wide range of body composition parameters is possible [ 17 , 18 ].…”

Athlete or Non-athlete? This Is the Question in Body Composition

“…Depending on the resistance and reactance of each tissue, different body composition components can be determined. To date, several predictive equations have been developed considering different populations (Campa et al, 2021;Coratella et al, 2021), and importantly different predictive equations provide different outcomes when used on the same subjects (Pichard et al, 1997;Coratella et al, 2021). Therefore, an accurate choice of predictive formulas is needed.…”

“…Despite their body composition features, some exercisers could not have the requisites to be defined as athletes, and consequently body composition might be estimated less accurately using equations developed for the general population. In this regard, the error would derive from the fact that a group of exercisers, having similar body composition characteristics to those of the subjects involved in the studies that have validated the formulas for athletes, would result in greater accuracy when equations for athletes are used (Coratella et al, 2021). Unfortunately, body composition characteristics cannot be discovered until a method of analysis is applied.…”