Author(s): GARCÍA ORTIZ, C., RANIERI, L.E., SOLANO, V., FERNÁNDEZ-SÁNCHEZ, J., TRUJILLO-COLMENA, D., RODRÍGUEZ-CASTAÑO, A., COLLADO-MATEO, D., CASADO, A., DEL COSO, J., Institution: REY JUAN CARLOS UNIVERSITY, Country: SPAIN, Abstract-ID: 2563

INTRODUCTION:
Accumulating evidence suggests that the female hormonal profile during the menstrual cycle could be a relevant factor in the regulation of substrate metabolism during endurance exercise. Estrogen has been associated with enhanced lipid oxidation whereas progesterone may attenuate these effects, potentially leading to menstrual cycle phase-dependent differences in fuel utilization[1]. Despite these proposed mechanisms, findings remain inconsistent, especially under steady-state conditions performed at intensities that maximize fat oxidation. Thus, the aim of this study was to investigate fat and carbohydrate oxidation during steady-state running performed at individual Fatmax intensity across three phases of the menstrual cycle.
[1]Oosthuyse et al., 2022
METHODS:
Fourteen young, physically active (V̇O2max=47.27±4.08 mL/min/kg), naturally menstruating women participated in a randomized crossover study consisting of a 60-min run at Fatmax intensity during three menstrual cycle phases: (a) early follicular, (b) periovulatory, and (c) mid-luteal. These phases were individually determined via mobile app tracking for 5 months, urinary luteinizing hormone tests, and daily tympanic temperature and body mass measurements. During exercise, breath-by-breath ventilatory data were collected with a gas analyzer to calculate fat and carbohydrate oxidation via stoichiometry equations. In addition, muscle oxygen saturation was measured with a Moxy monitor, heart rate was recorded using a chest-strap monitor, and rating of perceived exertion was assessed using the Borg 6–20 scale. Data were analyzed using linear mixed-effects models.
RESULTS:
No main effect of menstrual cycle phase was found on total fat oxidized (34.5±9.3, 37.0±9.3 and 35.4±9.1 g for early follicular, peri-ovulatory, and mid-luteal, respectively; p=.424), total carbohydrate oxidized (p=.460), or total energy expended (p=.244) during exercise. Additionally, there was no effect of the menstrual cycle phase on mean muscle oxygen saturation (p=.417) or perceived exertion (p=.084). However, a main effect of the menstrual cycle phase was found in mean heart rate, with higher heart rate in the peri-ovulatory compared to the early follicular phase (p=.049). Additionally, there was a main effect of the phase on the mean respiratory frequency with higher values during mid-luteal phase compared to early follicular (p=.035) and peri-ovulatory phases (p=.022).
CONCLUSION:
In summary, menstrual cycle phase did not influence substrate oxidation, total energy expenditure, muscle oxygen saturation, or perceived exertion during steady-state running at Fatmax intensity. These findings suggest that fluctuations in ovarian hormones do not meaningfully alter fuel utilization under these exercise conditions. However, phase-dependent differences were observed in selected cardiorespiratory variables with a higher heart rate during the periovulatory phase and elevated respiratory frequency during the mid-luteal phase.