Sammendrag
Abstract
Background
Previous studies have demonstrated conflicting results regarding substrate metabolism across the menstrual cycle (MC). While some studies suggest that substrate metabolism may vary across MC phases with potential higher carbohydrate metabolism in the early follicular phase (EF) and increased fat metabolism in the mid luteal phase (ML), particularly with a higher oestrogen/progesterone ratio (E2/P4 ratio), others report no significant differences.
Aim
The primary aim of the current study was to investigate the effect of MC phase effects, capillary blood glucose concentration (CBGl) and respiratory exchange ratio (RER) during high- vs. low-intensity training sessions (HIT and LIT), by adhering to established guidelines for conducting research on the MC. The secondary aim was to consider how the change in E2/P4 ratio (∆ = ML-EF) influences these variables.
Methods
Endurance-trained female participants (n = 10) completed HIT and LIT sessions in the lab in each of the three phases, while running or cycling. MC phases (i.e., EF, ovulatory phase (O), and ML) were determined using calendar-based counting, ovulation kits and subsequently confirmed using venous hormone analysis.
Results
CBGl and RER were significantly lower in ML compared to EF (-0.53 ± 0.32 mmol/L, p-value = 0.01; and -0.04 ± 0.03, p-value = 0.04 respectively) during HIT. The results showed no differences in CBGl or RER during LIT. There was no correlation between the change in E2/P4 ratio from EF to ML and the change in CBGl from EF to ML during HIT or between the change in RER from EF to ML during HIT and LIT. For the change in CBGl from EF to ML and the change in E2/P4 ratio from EF to ML during LIT, a large positive correlation (p = 0.01; r = 0.60) was found.
Conclusions
MC phase seems to affect substrate metabolism during HIT, with lower CBGl and RER values during ML compared to EF. Changes in E2/P4 ratio from EF to ML are not correlated with changes in CBGl or RER from EF to ML during HIT. During LIT an increased change in E2/P4 ratio from EF to ML suggests a larger change in CBGl from EF to ML. These findings indicate that both MC phase and the magnitude of the change in E2/P4 ratio from EF to ML affect substrate metabolism.