Effect Of Menstrual Cycle On Oxygen Dynamics During Endurance Exercise

INTRODUCTION: Several studies have examined the effects of the menstrual cycle on muscle strength and endurance capacity. While many studies conclude that fluctuations in hormone secretion influence exercise performance, the findings are not uniform. Few studies, however, have investigated how oxygen uptake, circulation, and utilization, key factors for muscle activity during exercise, are affected by the menstrual cycle, which alters fluid volume and blood composition in the body. PURPOSE: This study aims to explore the effects of the menstrual cycle on oxygen dynamics during endurance exercise by observing oxygen uptake (VO2) and percutaneous oxygen saturation (SpO2) during physical activity. METHODS: Six healthy women (age: 21.0 ± 7.0 years) with stable menstrual cycles participated in the study. Each participant performed endurance exercise using a cycle ergometer in three phases of the menstrual cycle: menstrual, follicular, and luteal phases. VO2 and SpO2 were measured during exercise, and the experiment was terminated when the heart rate reached 150 beats per minute. A generalized linear mixed model (GLMM) was used to examine the relationship between VO2 and SpO2, with VO2 as the response variable, menstrual cycle phase and SpO2 as fixed effects, and subjects as random effects. RESULTS:Maximum oxygen uptake during cycling was highest in the follicular phase (23.9 ± 2.7 ml/min/kg), followed by the luteal phase (23.3 ± 4.4 ml/min/kg) and menstrual phase (22.8 ± 1.9 ml/min/kg), although no significant differences were found between the phases. Oxygen saturation was also highest in the follicular phase (98.7 ± 1.2%), compared to the luteal (98.5 ± 1.0%) and menstrual phases (98.4 ± 1.2%), but the variations between phases were minimal (within 1%) and not statistically significant. However, the GLMM analysis revealed heterogeneity in the luteal phase compared to the other phases of the cycle. CONCLUSIONS: This study suggests that oxygen uptake and oxygen saturation are not significantly affected by the menstrual cycle. However, the GLMM analysis revealed that the luteal phase exhibited unique oxygen dynamics compared to the other menstrual phases. These findings indicate that the body's oxygen supply during endurance exercise in the luteal phase may differ from other phases of the menstrual cycle. Supported by: This work was supported by FANCL CORPORATION.