Author(s): LAUXTERMANN, L., TRISKA, C.1,2, MATHY, A.1,2, PIRKER, V.1, SCHARHAG, J.1,3, WESSNER, B.1, Institution: UNIVERSITY OF VIENNA, Country: AUSTRIA, Abstract-ID: 1483

INTRODUCTION:
Almost 42% of female athletes report subjective impairments in various phases of the menstrual cycle (MC), but there is limited evidence for objective performance declines [1,2]. Fluctuations in oestrogen and progesterone may affect performance via changes in substrate metabolism [3]. Therefore, this study investigates the impact of the MC on oxygen uptake and fat metabolism in active, eumenorrheic women during submaximal endurance exercise.
METHODS:
The study lasted three full natural MCs (1 observation, 2 test MCs), during which six submaximal cycling tests were completed (two per menstrual phase (MP), late follicular phase (LFP), and mid-luteal phase (MLP)). The tests consisted of a square-wave step-transition protocol (25% (transition 1) and 65% (transition 2) of the difference between VT1 and maximal power; 6 min each; 20 W baseline). Breath-by-breath data, oxygen uptake kinetics, substrate utilization and total energy expenditure (TEE) were measured in both low-intensity (IL) and high-intensity (IH) intervals. Twenty-three of 27 interested women fulfilled the inclusion criteria with 18 completing the study. Finally, only 11 women (age: 26.9±4.7 yrs; BMI: 22.7±2.6 kg/m²; V̇O₂max: 45.7±4.9 mL/min/kg) showed a regular MC with ovulation and were included in the statistical analyses (means of the data from two MP, LFP or MLP measurements subjected to repeated-measures ANOVA).
RESULTS:
Blood oestrogen levels differed significantly between MC phases (p<0.001, η²p=0.800), with the highest levels in LFP, followed by MLP and MP (all p<0.05). Progesterone levels (p<0.001, η²p=0.919) were higher in MLP compared to LFP and MP (p<0.001). However, fat (p=0.478, η²p=0.071) and carbohydrate metabolism (p=0.430, η²p=0.081), respiratory exchange ratio rate (ΔRER: p=0.367, η²p=0.095), and lactate (Δlactate: p=0.088, η²p=0.216) did not differ between cycle phases (MP, LFP, MLP). In addition, oxygen uptake kinetics (IL: p=0.401, η²p=0.079; IH: p=0.378, η²p=0.093), TTE (IL: p=0.338, η²p=0.094; IH: p=0.382, η²p=0.080), heart rate (IL: p=0.647, η²p=0.027; IH: p=0.727, η²p=0.017), gross efficiency (p=0.789, η²p= 0.023), and RPE (IL: p=0.147, η²p= 0.175; IH: p=0.103, η²p=0.203) did not differ between phases at both intensities.
CONCLUSION:
Although hormone levels varied, performance and substrate metabolism did not differ significantly.The study’s three‐month observation period was a strength; however, excluding irregular cycles (52%) resulted in a small sample size insufficient to detect small‐ to medium‐effect differences. We suggest that, in addition to hormone levels, personalized (even subjective) measures should be considered to clarify the complex relationship between the MC and performance.
[1] Bruinvels, G., et al. (2016). PLoS One, 11(2), e0149881.
[2] McNulty, K.L., et al. (2020). Sports Med, 50(10), 1813-1827.
[3] Boisseau, N., & Isacco, L. (2022). Eur J Sport Sci, 22(5), 672–683