INVESTIGATING THE EFFECTS OF HORMONAL FLUCTUATIONS ASSOCIATED WITH MENSTRUAL CYCLE ON PEAK FAT OXIDATION DURING GRADED EXERCISE IN ENDURANCE-TRAINED WOMEN
Authors: Molloy Eoin , Murphy-Griffin Maria , Harrison Michael 
Published: January 2025

<p><strong>Background:</strong> The menstrual cycle (MC) and associated hormones have become a popular subject of discussion due to their potential impact on how women utilize energy sources during exercise. Previous research has reported MC does not affect performance and also MC does not affect peak fat oxidation (PFO). However, given the variability of hormonal concentrations over time their effects can be variable at different phases within the MC (1,2,7). <strong>Purpose:</strong> In this study, our aim was to assess if three different phases within the MC, mid follicular (MF), late follicular (LF) and mid-luteal (ML), had differing effects on peak fat oxidation and substrate utilisation due to varying hormones. <strong>Methods:</strong> A group of endurance-trained women (n=12) aged 37 (+/- 2.9 years) were randomly recruited and assigned to the mid-follicular (MF), late follicular (LF) or mid-luteal (ML) group. MC length was established, and within the MC the LF phase was firstly identified through the calendar method and subsequently through hormonal verification. Following calendar and hormonal verification of the LF phase, both MF and ML phases were identified using the same method. FATMAX tests combined with hormonal quantification were then conducted on each participant at each phase of interest following an overnight fast. <strong>Results:</strong> PFO occurred at 50 watts in the MF and LF phase with PFO occurring at 35 watts in the ML phase. PFO at the MF phase was 0.344g/min, it was 0.345g/min at LF and was 0.275g/min at the ML phase. Further analysis highlighted that there was no difference between PFO rates at MF and LF (p&gt;0.05). There was a difference in PFO rates between MF and ML, but this difference was marginal but not significant (p=0.11). Differences in PFO rates between LF and ML were found to be significant (p&lt;0.05). More in-depth analysis utilising a One-way ANOVA for fat oxidation rates at each stage across the complete FATMAX test found no significant difference at any stage in fat oxidation rates (p&gt;0.05). When peak CHO oxidation was calculated, results outlined 1.78g/min during the MF phase, 1.79g/min during the LF phase and 2.02g/min during the ML phase and all at 125 watts. When CHO oxidation rates were statistically analysed at each intensity utilising a One Way Anova, there was no difference in CHO oxidation rate irrespective of the phase. When peak CHO was assessed via a T test in pairs, MF V LF (p&gt;0.05), MF V LF (p&gt;0.05) and LF V ML (p=0.13) there was no significant difference. When hormone concentrations were assessed in pairs (MF v LF, MF v ML &amp; LF v ML) at the three points of interest within the MC, utilising the paired sample t-test it was noted that there was no significant difference between E3G concentrations at MF to LF (p=0.12), MF to ML (p=0.29) and LF to ML (p=0.12). Similarly, PdG concentrations were assessed, and it was highlighted that between MF to LF there was no difference (p&gt;0.05), however, MF to ML and LF to ML concentrations of PdG were significantly different (p&lt;0.05). LH concentrations were statistically analysed also employing the paired sample t-test, and it was observed to be significantly different from MF to LF (p&lt;0.05) and LF to ML (p&lt;0.05) but MF to ML was not significant (P&gt;0.05). In conclusion, a significant difference in PFO was detected between LF and ML phases, but no difference in PFO was observed between MF and LF phases or MF and ML phases. Also, no difference in Fat oxidation or CHO oxidation was detected between any phase at each intensity.</p><p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/soc/0739/a.php" alt="Hit counter" /></p>