Females have been underrepresented in sports science studies, partly because hormonal changes can complicate high-quality study designs. Doctoral researcher Ida Löfberg studied how resting energy expenditure and fat use during exercise change across the menstrual cycle or combined oral contraceptive use. The study also investigated how eight weeks of endurance training influence resting energy expenditure and body composition. Participants were recreationally active females aged 18–35.
The results showed that resting energy expenditure was, on average, slightly higher in the luteal phase (the second half of the menstrual cycle) than at the beginning of the cycle. During the luteal phase, blood levels of the satiety hormone leptin were also higher, and the active thyroid hormone triiodothyronine showed a similar pattern. However, the change in resting energy expenditure was small relative to the typical day-to-day variation, suggesting that the practical relevance of this finding is limited.
Fat use as fuel during exercise did not differ between menstrual cycle phases. Females using combined oral contraceptives showed slightly higher fat use during exercise than females not using contraceptives, but the differences were largely explained by differences in fat-free mass and cardiorespiratory fitness.
Eight weeks of endurance training slightly improved peak oxygen uptake but did not clearly change resting energy expenditure or body composition. Training adaptations were similar regardless of the menstrual cycle phase or hormonal contraceptive use.
Overall, the findings suggest that the menstrual cycle or oral contraceptive use does not appear to have major effects on resting energy expenditure, fat use, or adaptations to endurance training in most females. The results help put hormone-related variation into perspective for both practice and research, and highlight the multifactorial regulation of energy metabolism. This may support the inclusion of females in metabolic research and help redefine the assumptions about the cycle-related metabolic changes. Future research should examine whether hormonal effects differ in athletes or over longer time periods.
MSc Ida Löfberg’s doctoral dissertation in exercise physiology, “Endogenous Hormones, Energy Metabolism and Body Composition in Females of Reproductive Age – Perspectives from Endurance Exercise”, will be examined at the University of Jyväskylä in the main building, hall C1, starting at 12:00 on 14 March 2026. The opponent will be Professor Karsten Köhler (Technical University of Munich, Germany) and the custos senior lecturer Ritva Mikkonen (University of Jyväskylä). The event will be held in english.
Further information:
Ida Löfberg, ida.i.lofberg@jyu.fi, +358442498704
