BODY-FAT PERCENTAGE AND GENDER - ASSOCIATIONS WITH EXERCISE ENERGY-EXPENDITURE, SUBSTRATE UTILIZATION, AND MECHANICAL WORK EFFICIENCY

Energy expenditure GEE) was measured at specific steady-state work rat es to determine if body fat percentage or gender was associated with e xercise EE, substrate oxidation, or work efficiency. Body fat percenta ge (leaner vs. fatter men, 9-15% vs. 20-25% fat; leaner vs. fatter wom en, 16-24% vs. 32-48% fat) was not related to work efficiency or subma ximal EE. Fatness affected substrate oxidation in men but not in women . Compared to fatter men, leaner men had higher fat oxidation (6.7 +/- 1.6 vs. 1.4 +/- 2.0 mg . kg fat-free mass [FFM](-1). min(-1); p < .01 ) and lower carbohydrate oxidation (26.6 +/- 4.2 vs. 39.3 +/- 5.0 mg . kg FFM(-1). min(-1); p < .01) at 60% VO2 max. When men and women of s imilar fatness and relative aerobic capacity were compared, men had hi gher EE measured as kilojoules per minute but similar rates of EE and substrate oxidation per kilogram of FFM at 40-60% VO(2)max. It was con cluded that body FFM, not fatness, is a determinant of exercise EE, wh ereas fatness is associated with differences in exercise substrate oxi dation in men. Along with aerobic fitness, gender and fatness should b e considered in future studies of exercise substrate oxidation.