Fat Oxidation and Aerobic Fitness in Postmenopausal Women

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Menopause is related to reduced fat oxidation capacity, limiting energy for submaximal activity, contributing to earlier fatigue, reducing aerobic performance and making physical activity more difficult. Exercise interventions can increase fat oxidation in sedentary postmenopausal women, but the degree to which this enhances aerobic performance is unknown. It is also unclear if postmenopausal interventions generate fat oxidation and fitness levels similar to women who are physically active before, during, and after menopause.

PURPOSE: To evaluate the effects of exercise on fat oxidation and aerobic fitness in postmenopausal women by comparing a short-term intervention in sedentary women to long-term exercisers.

METHODS: Two cohorts were studied for 16 weeks: 1) Active cohort (N = 13), exercised > 5 hr/wk for ≥10 years; 2) Training cohort (N = 14), sedentary, completed 16-week, 1000 MET[BULLET OPERATOR]min[BULLET OPERATOR]week-1 intervention. Gas exchange was measured at rest and during cycle ergometer maximal exercise tests. Fat oxidation was calculated from RER at rest and during warmup and exercise phases of the cycle test. Fitness variables were workloads and oxygen consumption at ventilatory threshold (workloadVT, VO2VT) and maximal exertion (workloadMAX, VO2MAX). Body composition was measured with DXA to normalize O2.

RESULTS: At baseline, compared to the Active cohort, the Training cohort had less fat-free mass (P = 0.04), used 15.7% less fat energy at rest (P = 0.02) and 9.7% less fat energy during warmup (P = 0.02), had a 46 W lower workloadMAX (P < 0.01), 3.6 ml O2[BULLET OPERATOR]kgFFM-1[BULLET OPERATOR]min-1 lower VO2VT (P < 0.01), and 8.2 ml O2[BULLET OPERATOR]kgFFM-1[BULLET OPERATOR]min-1 lower VO2MAX (P < 0.01). At 16-weeks the Active cohort’s values did not change, but the Training cohort increased fat energy during warmup (+12%; P = 0.02), workloadVT (+9 W; P < 0.01), workloadMAX (+16 W; P < 0.01), and VO2MAX (+2.6 ml O2[BULLET OPERATOR]kgFFM-1[BULLET OPERATOR]min-1; P < 0.01). At 16 weeks the cohorts differed for fitness, but did not differ for fat energy during warmup (P = 0.25). Change in fat oxidation was not correlated with change in aerobic fitness.

CONCLUSION: Exercise interventions improve fat oxidation and aerobic fitness in sedentary postmenopausal women. Increased fat oxidation approaches the level of long-term postmenopausal exercisers, but fitness gains are not as marked and are not explained by increased fat oxidation.