Relationship between leucine oxidation and oxygen consumption during steady-state exercise

Purpose: The purpose of this study was to assess the relationship between w hole-body leucine oxidation and oxygen consumption during steady-state exer cise. Our hypothesis was that leucine oxidation will he responsive to incre ased whole-body energy needs. Methods: Sixteen healthy individuals (7 women and 9 men) were infused with a stable isotope of leucine and, for comparis on purposes, lysine during 60 min of moderate-intensity exercise. Results: Leucine oxidation was increased (P < 0.05) and nonoxidative leucine disposa l was decreased (P < 0.05), whereas leucine and lysine rate of appearance r emained unchanged (P = NS) during exercise. Linear regression analysis indi cated a modest relationship between leucine oxidation and steady-state oxyg en consumption (R = 0.69; P < 0.003) during steady-state exercise. The coef ficient of determination (R-2 = 0.49) indicates that approximately half of the variance in whole-body leucine oxidation during exercise can be explain ed by whole-body oxygen consumption. Conclusion: In a statistically appropr iate sample size of humans whose dietary intake was controlled, the whole-b ody rate of leucine oxidation during exercise was only partially influenced by energy demands.