Author(s): DOCTER, H., TAYLOR, M., MÜLLER, A., OSBORNE, J.O., SANDBAKK, Ø., DE KONING, J.J., NOORDHOF, D.A., Institution: NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY, Country: NORWAY, Abstract-ID: 2429

INTRODUCTION:
In addition to maximal oxygen uptake (V̇O2max), fractional utilization of V̇O2max, and efficiency1, durability has been regarded as an important determinant of endurance performance2. Durability may be reflected by the change in any of the three other determinants over time,3. In women, a drop in repeated sprint performance following a simulated cycling race is exacerbated in the mid luteal phase4. However, it is unclear if menstrual cycle phase influences the ability to maintain efficiency. This study aimed to evaluate the ability to maintain efficiency after completing a high-intensity training session, and whether this ability is influence by the menstrual cycle.
METHODS:
Twenty-four female endurance-trained females performed a high intensity training session (5x5min at 80% of velocity or power output at V̇O2max, 2min rest) on a treadmill or cycle ergometer in the early follicular (EF), ovulatory (O), and mid luteal (ML) phase of one menstrual cycle. Menstrual cycle phases were determined using the determined using calendar-based counting, urinary ovulation testing, and analysis of ovarian hormones. Metabolic power per kg body mass was calculated using gas exchange data during submaximal exercise (60% of velocity or power output at V̇O2max) before and after each training session and used as a measure of efficiency.
RESULTS:
A multilevel linear model revealed a higher metabolic power after the training session (p=0.041, r=0.24) compared to before. A second model revealed that menstrual cycle phase did not significantly affect the change in metabolic power (EF vs. O: p=0.388, r=0.16, O vs. ML: p=0.306, r=0.19), although a medium effect size was found between the EF and ML phase (p=0.058, r=0.35; mean±SE running EF: -0.51±6.31W/kg, O: 6.04±14.9W/kg, ML: 13.96±6.82W/kg; cycling EF: -2.86±15.0W/kg, O: 3.69±6.65W/kg, ML: 11.6±14.9W/kg). The population of interest makes the study vulnerable for small sample sizes, which may have led to a low statistical power.
CONCLUSION:
Efficiency is reduced following a high-intensity training session. There is some indication that the ability to maintain efficiency may be more compromised in the ML compared to the EF phase. However, due to the low statistical power no conclusions on the effect of menstrual cycle phase on durability can be drawn.


References:
1 Joyner MJ, Coyle EF. (2008) J Physiol. 586(1):35-44.
2 Jones, A. M. (2023). J Physiol. 0: 1–16
3 Matomäki, P., Heinonen, O. J., Nummela, A., Laukkanen, J., Auvinen, E. P., Pirkola, L., & Kyröläinen, H. (2023). Front. in Physiol., 14: 203.
4 Lee, S. J., Sim, M., Van Rens, F. E., & Peiffer, J. J. (2023). MSSE. 56(1): 92-102