It is unknown whether increased resting energy expenditure (REE) in athletes is due to changes in organ-tissue mass and/or metabolic rate. The purpose of this study was to investigate the effect of the organ-tissue component of fat-free mass (FFM) on absolute and relative REE (the REE/FFM ratio) for heavy-weight athletes. We examined the relationship between the REE measured by indirect calorimetry and the REE calculated from organ-tissue mass. Ten heavy-weight athletes (Sumo wrestlers) and 11 moderately active male students (controls) were recruited to participate in this study. FFM was measured by two-component densitometry. Contiguous magnetic resonance imaging (MRI) images with a 1cm slice thickness were obtained from the parietal to the ankle joints, and the cross-sectional area and volume were determined for each type of organ-tissue. The volume units were converted into mass by an assumed constant density. The measured-REE was determined by indirect calorimetry. The calculated-REE was estimated as the sum of individual organ-tissue masses multiplied by their metabolic rate constants. The measured-REE for Sumo wrestlers (2286kcal/day) was higher (P<0.01) than for controls (1550kcal/day), but the measured-REE/FFM ratio was similar between the two groups (Sumo wrestlers 29.1kcal/kg/day vs. controls 29.3kcal/kg/day). Sumo wrestlers had a greater amount of FFM and FFM components (e.g., skeletal muscle (SM), liver and kidney) except for brain, while the proportion of organ-tissue mass to FFM was not different between the two groups except for liver. The absolute and relative measured-REE values for Sumo wrestlers were not significantly different from the respective calculated-REE values. The REE for heavy-weight athletes can be attributed not to an elevation of the organ-tissue metabolic rate, but to a larger absolute amount of low and high metabolically active tissue including SM, liver and kidney.
High ree in heavy-weight athletes attributed to large organ-tissue mass
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