Riley Galloway1, Scott Owens2, Heontae Kim2, Martha Bass2, Minsoo Kang2, Mark Loftin, FACSM2. 1The University of Southern Mississippi, Hattiesburg, MS. 2The University of Mississippi, University, MS.

Background: VO2max is typically expressed relative to body mass (ml/min/kg), however, this expression is often biased with respect to variance in body dimensions such as mass and stature. This study sought to identify the most appropriate allometric scaling model used to express aerobic fitness, determined by VO2max, that would allow comparisons across differing body types. Methods: VO2max and body composition data were collected from untrained non-obese and obese participants (N=126). Total body mass (BM), fat-free mass (FFM), and combined leg fat-free mass (LFFM) were used as allometric scaling models to determine the goodness of fit using the Akaike information criterion (AIC) technique. Results: Allometric scaled exponents adjusted for BM, FFM and LFFM were 0.67, 0.68 and 0.55, respectively. VO2max scaled to BM was 22% higher in non-obese individuals. Scaled to LFFM, VO2max was only 7.5% higher in non-obese individuals as compared to obese individuals. Data showed a positive correlation (r=0.28; p=0.009) between VO2max and BM for non-obese participants while a negative correlation (r=-0.39; p=0.014) was present in the obese participants. AIC values showed the LFFM model as the best fit and the AIC differences for FFM and BM were both >10 “no support” for the model (12.1 and 28.2, respectively). Conclusion: Allometric scaling of VO2 max with the LFFM model provides the best representation aerobic power (AICc = 0 “substantial support). Traditional relative VO2max, expressed scaled to BM, offers “essentially no support” according to the AIC difference values (>10) and introduces a bias when comparing individuals of various body sizes and compositions. These results indicate that VO2max scaled to BM alone, in obese individuals, reflects the level of adipose tissue more so than functional capacity. Interpretation of aerobic power and comparisons would be most appropriate when allometrically scaled to the metabolically active tissue, in this case, LFFM. The lower mass exponent of 0.55 for LFFM and smaller proportional increase in VO2max indicates a greater scaling precision of VO2max. This assists in correcting the bias created when scaling to BM by partitioning out the effect of whole-body size and focusing on the primary involved musculature.

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