Author(s): DEL COSO GARRIGÓS, J., GARCÍA-ORTIZ, C., RANIERI, L.E., SOLANO, V., FERNÁNDEZ-SÁNCHEZ, J., TRUJILLO-COLMENA, D., RODRÍGUEZ-CASTAÑO, A., COLLADO-MATEO, D., CASADO, A., Institution: REY JUAN CARLOS UNIVERSITY, Country: SPAIN, Abstract-ID: 2324

INTRODUCTION:
Menstrual cycle phases are characterized by distinct hormonal profiles that have been hypothesized to modulate thermoregulatory and fluid balance responses to endurance exercise (1). Progesterone is associated with a rightward shift in the thermoregulatory set point during the luteal phase, resulting in elevated basal body temperature and potentially greater thermoregulatory strain during exercise. In addition, progesterone has been linked to lower sweat rates as well as increased aldosterone and sodium retention levels, yet findings remain inconsistent, partly due to imprecise phase identification. This study examined whether thermoregulatory and fluid balance responses differ across menstrual cycle phases during endurance running in temperate conditions.
METHODS:
Fourteen physically active, naturally menstruating women (age= 28±4 years; V̇O2max= 47.27±4.08 mL/kg/min) completed a randomized crossover study consisting of 60 min of treadmill running at moderate intensity in temperate conditions (21.3±0.1ºC, 43.6±1.2% humidity) during three menstrual cycle phases: (a) early follicular, (b) peri-ovulatory, (c) and mid-luteal. Phases were individually identified using a multimethod approach including mobile app tracking of the previous five cycles, urinary luteinizing hormone test strips to detect ovulation, and daily waking measurements of tympanic temperature and body mass. Body mass changes were used to calculate dehydration and sweat rate. Whole-body sweat sodium concentration ([Na+]sweat) was determined from sweat patches placed at seven anatomical sites. Tympanic temperature and perceptual responses (thermal sensation and thirst) were recorded during exercise. Menstrual symptoms were assessed before exercise using the menstrual symptom questionnaire (MSQ; 0-95 arbitrary units, [a.u.]). Data were analyzed using linear mixed models and are presented as estimated means ± SD.
RESULTS:
There was no main effect of menstrual cycle phase on sweat rate (0.52±0.15, 0.49±0.17 and 0.50±0.16 L/h, for early follicular, peri-ovulatory and mid-luteal, respectively; p= 0.282), whole-body [Na⁺]sweat (44.2±9.9, 42.8±10.0 and 40.3±9.8 mmol/L; p= 0.431), mean tympanic temperature (36.7±0.1, 36.7±0.2 and 36.7±0.2 ºC; p= 0.295), thermal sensation (p= 0.753) or thirst (p= 0.490) during exercise. MSQ scores differed across phases (p= 0.001), with higher symptom scores in the early follicular phase, followed by mid-luteal and peri-ovulatory phases (12.5±6.0 > 9.9±5.3 > 5.9±3.5 arbitrary units, respectively; all p< 0.050)
CONCLUSION:
Thermoregulatory and fluid balance responses to 60 min of moderate-intensity running in temperate conditions do not differ across menstrual cycle phases in physically active, naturally menstruating women. However, menstrual symptoms vary across the cycle, suggesting that symptom management during the early follicular and mid-luteal phases may improve exercise comfort.
(1) Rodriguez‐Giustiniani, et al. EJSS (2022)