Abstract
This study examined the effect of estradiol-β-17 across the menstrual cycle (MC) during aerobic exercise on energy substrate utilization and oxidation. Thirty-two eumenorrheic (age = 22.4 ± 3.8 y (mean ± SD)), physically active women participated in two steady-state running sessions at 65% of VO2max, one during the early follicular and one during the luteal phase of the MC. Blood samples were collected at rest before each exercise session and analyzed for Estradiol-β-17 to confirm the MC phase. Carbohydrate (CHO) utilization and oxidation values were significantly lower (p < 0.05) in the luteal (utilization: 51.6 ± 16.7%; oxidation: 1.22 ± 0.56 g/min; effect size (ES) = 0.45, 0.27) than follicular phase (utilization: 58.2 ± 15.1%; oxidation: 1.38 ± 0.60 g/min) exercise sessions. Conversely, fat utilization and oxidation values were significantly (p < 0.05) higher in the luteal (utilization: 48.4 ± 16.7%; oxidation: 0.49 ± 0.19 g/min; ES = 0.45,0.28) than follicular phase (utilization: 41.8 ± 15.1%; oxidation: 0.41 ± 0.14 g/min). Estradiol-β-17 concentrations were significantly (p < 0.01) greater during the luteal (518.5 ± 285.4 pmol/L; ES = 0.75) than follicular phase (243.8 ± 143.2 pmol/L). Results suggest a greater use of fat and reduced amount of CHO usage during the luteal versus follicular phase, directly related to the change in resting estradiol-β-17. Future research should investigate the role these changes may play in female athletic performance.
Highlights
The number of women engaged in exercise activities for health as well as sporting endeavors has grown exponentially in recent decades [1]
Eumenorrheic adult women display large fluctuations in reproductive hormone concentrations throughout a menstrual cycle [2]; low estrogen and progesterone at menses with elevations beginning at ovulation and continuing into the luteal phase)
Forty women were recruited into the study, of which 32 completed all aspects of our protocol which involved three laboratory sessions: (i) an orientation session involving the determination of maximal oxygen uptake (VO2max ), and two submaximal steady-state running sessions at 65% VO2max, (ii) once during the early follicular, and (iii) once during the luteal phase of the menstrual cycle
Summary
The number of women engaged in exercise activities for health as well as sporting endeavors has grown exponentially in recent decades [1]. The number of research studies examining female physiological responses to exercise has grown too, the total amount of work is far less than in men and more research is still needed [1]. This last point is warranted as the unique aspects of a woman’s physiology, especially relative to the influence of the menstrual cycle and reproductive hormones, is critical to understand scientifically since many of the findings in male-based studies cannot and should not be directly applied to women (i.e., “women are not small men”; Dr Stacy Sims quote). The depiction of distinct phases within a menstrual cycle—menses, follicular, ovulation, and luteal—have traditionally been used to characterize the underlying reproductive
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