Author(s): RATTLEY, K., DEWHURST, S., FELTON, M., NEAL, R., Institution: BOURNEMOUTH UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 1829

INTRODUCTION:
There is a decrease in daily energy expenditure in women during mid-life regardless of menopause stage, but oestrogen deficiency also leads to reduced resting, sleeping, exercise and total energy expenditure. Identifying the deficit in exercise energy expenditure that can be attributed to menopause will aid the development of specific exercise prescription guidance, which may support healthy ageing in and after menopause. This study aimed to evaluate the impact of perimenopause and postmenopause on exercise energy expenditure and respiratory exchange ratio during exercise to maximal intensity.
METHODS:
53 women (PRE: 27 ± 4 yr; PERI: 47 ± 5 yrs; POST: 55 ± 3 yrs; 167.8 ± 5.2 cm, 69.3 ± 9.8 kg), categorised as premenopausal (PRE, n=16), perimenopausal (PERI, n=17) and postmenopausal (POST n=20), completed a maximal aerobic capacity (VO2 max) ramp test on a cycle ergometer, with expired gases measured throughout. Body composition was assessed by bioelectrical impedance. Resting plasma oestradiol, measured by enzyme linked immunosorbent assay (ELISA), was used to confirm menstrual status. Naturally menstruating premenopausal and perimenopausal women were tested during the early follicular phase (1-7 days after starting menstruation), and postmenopausal or hormonal contraceptive users at earliest convenience. Respiratory exchange ratio (RER), energy expenditure, and fat-carbohydrate oxidation crossover point were evaluated between groups using mixed-effects analysis of variance.
RESULTS:
Throughout the test, there were differences in energy expenditure between groups (p = 0.02), with the PRE group demonstrating a higher energy expenditure (9.6 ± 3.1 kcal·min-1) than the POST group (8.2 ± 2.7 kcal·min-1) (p<0.05). Body fat mass was different between groups (PRE: 15.6 ± 5.9kg; PERI: 19.8 ± 7.0kg; POST: 22.5 ± 10.1kg, p = 0.05). When normalised for body fat mass, differences in energy expenditure remained (PRE: 0.72 ± 0.22 kcal·min-1·kgBFM; PERI: 0.53 ± 1.9 kcal·min-1·kg·BFM; POST: 0.43 ± 0.14 kcal·min-1·kg·BFM; p<0.01), with PRE energy expenditure greater than POST energy expenditure throughout (p<0.05). There were no differences in the RER (PRE: 0.97 ± 0.13; PERI: 0.96 ± 0.13; POST: 0.96 ± 0.13, p = 0.49) or the exercise intensity at which fat-carbohydrate oxidation crossover occurred between the groups (PRE: 49.6%; PERI: 52.1%, POST: 54.0% of VO2 max, p>0.05).
CONCLUSION:
Menstrual status did not impact RER during exercise; this is the first study to evidence that menopause has no effect on RER throughout a maximal exercise test. However, in postmenopause energy expenditure may be limited across all intensities during a maximal exercise test suggesting a ceiling effect potentially linked to increased body fat mass. Further research should evaluate the responses to ecologically valid doses of exercise of women across the lifecycle to better understand the changes that occur and the role of oestrogen deficiency in menopause.