Menstrual phase and ambient temperature do not influence iron regulation in the acute exercise period

Abstract

The current study investigated whether ambient heat augments the inflammatory and post-exercise hepcidin response in women, and if menstrual phase and/or self-pacing modulate these physiological effects. Eight trained females (age: 37±7 y; VO2max: 46±7 mL∙kg-1∙min-1; peak power output: 4.5±0.8 W∙kg-1) underwent 20 min of fixed-intensity cycling (100 and 125 W) followed by a 30-min work trial (≈75% VO2max) in a moderate (MOD: 20±1 °C, 53±8% relative humidity) and warm-humid (WARM: 32±0 °C, 75±3% relative humidity) environment in both their early follicular (days 5±2) and mid-luteal (days 21±3) phases. Mean power output was 5±4 W higher in MOD than in WARM (p=0.02) such that the difference in core temperature rise was limited between environments (-0.29±0.18 °C in MOD, p<0.01). IL-6 and hepcidin both increased post-exercise (198% and 38%, respectively), however, neither were affected by ambient temperature or menstrual phase (all p>0.15). Multiple regression analysis demonstrated that the IL-6 response to exercise was explained by leukocyte and platelet count (r2=0.72, p<0.01) and the hepcidin response to exercise was explained by serum iron and ferritin (r2=0.62, p<0.01). During exercise participants almost matched their fluid loss (0.48±0.18 kg·h-1) with water intake (0.35±0.15 L·h-1) such that changes in body mass (-0.3±0.3%) and serum osmolality (0.5±2.0 mOsm·kg-1) were minimal or negligible, indicating a behavioral fluid-regulatory response. These results indicate that trained, iron sufficient women suffer no detriment to their iron regulation in response to exercise with acute ambient heat stress or between menstrual phases on account of a performance-physiological trade-off.

Measurement error of self-paced exercise performance in athletic women is not affected by ovulatory status or ambient environment

“…All were healthy, non-smokers and free from cardiovascular, metabolic, neurological, and respiratory diseases and were not taking any regular medication apart from those using the OCP. Some of the data herein have been reported previously in separate studies (16)(17)(18). All eumenorrheic females self-reported a regular menstrual cycle 21-35 days in length (≥3 mo) with no use of hormonal contraception (≥6 mo).…”

“…All previous studies (16)(17)(18) had received approval by the Massey University Human Ethics Committee (Southern A) and were performed in accordance with the latest revision of the Declaration of Helsinki, except for registration in a database. Informed, written consent was obtained from all participants prior to participation.…”

“…The primary purpose of the current study was to determine whether ovulatory/hormonal status or ambient profile were moderating variables for measurement error of a 30-min self-paced work trial, whilst a secondary purpose was to add exercise performance norms specific to athletic women to the literature. Given that our previous studies (16)(17)(18) observed no (quasi-) menstrual phase-by-ambient profile interaction effect for work completed or mean power output, we hypothesized 113 that measurement error would be unaffected by these factors. 114…”

“…Given the arguments above, there appears to be a lack of literature describing typical variance of the most commonly utilized exercise testing used for assessing the female physiological response: laboratory cycle ergometry of >20 min duration. We have previously reported that the (quasi-) menstrual phase did not influence performance of a 30-min work trial, whereas the ambient profile (increased temperature and humidity) reduced work performed by 3-5% (16)(17)(18). Considering that the ~2 weeks separating trials between (quasi-) menstrual phases did not affect exercise performance, we used this (within-environment) design to determine test-retest reliability in a homogenous sample of aerobically-trained women.…”

Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms

“…This supports the notion that females may be predisposed to less heat dissipation through evaporative heat loss, potentially exacerbating the physiological consequences of exercise-induced dehydration. However, an emerging body of evidence suggests that well-trained females may be less severely impacted by female sex hormones on thermoregulatory, cardiovascular, osmoregulatory, and exercise performance parameters (52)(53)(54). Accordingly, a greater breadth of research is required to unearth these nuances.…”