FUEL METABOLISM IN MEN AND WOMEN DURING AND AFTER LONG-DURATION EXERCISE

This study aimed to determine gender-based differences in fuel metabol ism in response to long-duration exercise. Fuel oxidation and the meta bolic response to exercise were compared in men (n = 14) and women (n = 13) during 2 h (40% of maximal O-2 uptake) of cycling and 2 h of pos texercise recovery. In addition, subjects completed a separate control day on which no exercise was performed. Fuel oxidation was measured u sing indirect calorimetry, and blood samples were drawn for the determ ination of circulating substrate and hormone levels. During exercise, women derived proportionally more of the total energy expended from fa t oxidation (50.9 +/- 1.8 and 43.7 +/- 2.1% for women and men, respect ively, P < 0.02), whereas men derived proportionally more energy from carbohydrate oxidation (53.1 +/- 2.1 and 45.7 +/- 1.8% for men and wom en, respectively, P < 0.01). These gender-based differences were not o bserved before exercise, after exercise, or on the control day. Epinep hrine (P < 0.007) and norepinephrine (P < 0.0009) levels were signific antly greater during exercise in men than in women (peak epinephrine c oncentrations: 208 +/- 36 and 121 +/- 15 pg/ml in men and women, respe ctively; peak norepinephrine concentrations: 924 +/- 125 and 659 +/- 6 8 pg/ml in men and women, respectively). As circulating glycerol level s were not different between the two groups, this suggests that women may be more sensitive to the lipolytic action of the catecholamines. I n conclusion, these data support the view that different priorities ar e placed on lipid and carbohydrate oxidation during exercise in men an d women and that these gender-based differences extend to the catechol amine response to exercise.