The effect of hormonal fluctuations in the menstrual cycle on running economy

The aim of this study was to examine the effects of fluctuations in ovarian hormones during a typical menstrual cycle on running economy (RE). In a repeated-measures design, ten eumenorrheic, moderately-trained runners (age: 32 ± 6 yrs, height: 169.4 ± 8.0 cm, and 58.4 ± 7.8 kg) completed four, weekly identical sub-maximal and maximal incremental step tests on a treadmill, in order to measure the possible physiological changes across a full menstrual cycle. For phase comparison, the results from the trials that fell in the early follicular (low oestrogen, low progesterone), late follicular (high oestrogen, low progesterone) and mid-luteal (high oestrogen, high progesterone) phases were used. There was a significant effect of menstrual cycle phase on RE (p < 0.001), with post hoc tests revealing that RE in the mid-luteal (ML) phase was decreased by 2.54 mL.kg-1.min-1 compared with the early follicular (EF) phase, and decreased by 2.22 mL.kg-1.min-1 compared with the late follicular (LF) phase. The ML phase also resulted in significantly elevated core temperature versus the EF (+ 0.51 ºC, p = 0.001) and LF phases (+ 0.66 ºC, p = 0.037), and elevated minute ventilation versus the EF phase (+ 3.83 L.min-1, p = 0.003). No significant effects (p ≥ 0.05) of menstrual cycle phase were found on body mass, heart rate, ratings of perceived exertion, time-to-exhaustion, maximal oxygen consumption, or blood lactate markers. The results of the study show that, as a result of high progesterone levels in the ML phase which causes increased core temperature and exercise ventilation, RE is decreased at exercise intensities that are applicable to training and performance. In physiologically stressful environments, this decrease in RE may have a significant impact on training and performance