Exercise Duration Affects Maximal Fat Oxidation In Post- Menopausal Women: Implications For Exercise Prescription

Abstract

The relative exercise intensity at maximal fat oxidation (FATmax, %VO2max) is used for exercise prescription for weight loss and metabolic health. In young men, FATmax is affected by exercise duration, with more prolonged testing protocols leading to higher values. PURPOSE: Since no data exist on post-menopausal women, we determined the effect of exercise duration on FATmax in this population. METHOD: 18 non-obese women (54±4 years; 4±3 years from menopause; 22±3 BMI) performed on a cycle ergometer a ramp test and 30-min steady-state trials at 40, 50, 60, 70 and 80% of the pre-determined VO2max. Based on VO2 and respiratory exchange ratio we calculated and compared (2-way RM ANOVA) absolute fat oxidation (FO, g-1·min-1) across intensities and duration. We compared FATmax derived from ramp (rFATmax), 5 (5FATmax) and 30-min data (30FATmax) (1-way RM ANOVA). We estimated FATmax using exercise duration (1, 5 and 30 min) and rFATmax as explanatory variables. RESULTS: FO was significantly affected by exercise duration, intensity and their interaction (for all p<0.001). Any exercise between 40 and 70% %VO2max, > 30 min, lead to an identical MFO (overall 0.21±0.09 g-1·min-1). 30FATmax occurred at a significantly higher %VO2max (57±10%) than rFATmax and 5FATmax (44±6 and 49±9%, not different). FATmax can be predicted from the linear combination of exercise duration (p<0.001) and rFATmax (p=0.01) as independent explanatory variables (r=0.69, SEE=8.8%). CONCLUSIONS: In post-menopausal women exercises at 40-80%VO2max of longer durations are associated with higher FATmax compared to ramp or short, steady-state sessions. Moreover, any intensity greater than rFATmax will maximize fat oxidation for exercises > 30 min. Finally, the intensity that maximizes fat oxidation can be predicted by exercise duration and rFATmax. This approach offers a valid approach for individualized exercise intensity prescription for weight loss and metabolic health in postmenopausal women.