Fat-free mass as a function of maximal oxygen consumption and 24-hour urinary creatinine, and 3-methylhistidine excretion

Abstract

The relationships between maximal oxygen consumption (VO2max) with fat-free mass (FFM), and with 24-h urinary excretion of 3-methylhistidine (3MH) and creatinine (Cr), were studied in 12 active men age 31.4 ± 9 yr (mean ± SD). FFM, VO2max and VO2maxWt−1 were 50.9 ± 9.1 kg, 3.8 ± 0.9 L · min−1, and 54.8 ± 9.4 ml · kg−1 · min−1, respectively. Urinary 3MH and Cr after 3 days on a meat-free diet were 213.9 ± 30.8 µmol · day−1 and 1.60 ± 0.3 g · day−1, respectively. 3MH · Cr−1 was 135.3 ± 16.8 µmol · g−1 or 15.3 ± 1.9 molar ratio × 103. The strongest (p < 0.01) associations found were 3MH versus FFM, FFM versus VO2max, and 3MH versus VO2max. Other significant (p < 0.05) relationships were Cr versus FFM, Cr versus 3MH, and Cr versus VO2max. Nonsignificant correlations were found for 3MH · Cr−1 versus VO2max kg−1 · min−1, 3MH · Cr−1 versus FFM, 3MH · Cr−1 versus VO2max, and FFM versus VO2max · kg−1 · min−1. The best predictor of FFM was 3MH. It was concluded that endogenous urinary 3MH excretion is a valid method to study human body composition and that 3MH is more closely related to FFM (r = 0.93) than VO2max (r = 0.78).