Author(s): MEKONNEN, E., MYLLE, I., WILLIAMS, J., YEOMAN, J., GOLDMAN, J., CLARKE, D., COATES, A., KRAUS, E., NAPIER, C., Institution: SIMON FRASER UNIVERSITY , Country: CANADA, Abstract-ID: 698

INTRODUCTION:
Running economy (RE) reflects the metabolic cost of running at a given submaximal speed and influences distance-running performance, particularly in trained athletes for whom VO2max and lactate threshold approach maximal levels [1]. In eumenorrheic females, RE may vary according to fluctuations in estrogen and progesterone levels across the menstrual cycle through effects on substrate utilization, cardiovascular regulation, and neuromuscular control [2]. However, evidence for menstrual cycle-related differences in RE remains inconsistent, largely due to indirect phase classification or two-phase study designs [2]. The purpose of this study was to examine metabolic responses to running across three hormonally distinct menstrual cycle phases.
METHODS:
Sixteen eumenorrheic trained female runners (age 28.4 +/- 5.9 y; BMI 20.7 +/- 2.2 kg/m^2; 5-km personal best: 16:30 - 27:00) completed an incremental treadmill running test during the early follicular (EF), late follicular (LF), and mid-luteal (ML) phases. We verified menstrual cycle phase using calendar tracking, urinary luteinizing hormone measurement, and serum estradiol and progesterone measurements. We measured oxygen consumption (VO2), heart rate (HR), and respiratory exchange ratio (RER). We modeled individualized phase-specific linear relationships between these variables and running speeds below the first ventilatory threshold (VT1) using linear mixed-effects models.
RESULTS:
Oxygen cost differed across menstrual-cycle phases (p = 0.046), with the highest cost in EF (0.173 +/- 0.035 L/min per km/h), followed by ML (0.164 +/- 0.027) and LF (0.151 +/- 0.036), with a significant EF-LF contrast (p = 0.014). Energetic cost showed a similar phase-dependent pattern (p = 0.043), with the highest cost in EF (0.889 +/- 0.179 kcal/min per km/h), followed by ML (0.845 +/- 0.138) and LF (0.788 +/- 0.169), and a significant EF-LF contrast (p = 0.013). Phase was not associated with differences in how HR or RER changed with speed (p = 0.739 and p = 0.329).
CONCLUSION:
Running economy differed across menstrual-cycle phases, with lower oxygen cost (better running economy) in the LF phase compared with the EF phase. Differences in energetic cost were primarily associated with differences in oxygen cost, as no differences were observed in RER or HR. Because VT1 corresponds to a sustainable intensity at which most endurance training volume is performed, these findings indicate that menstrual-cycle phase may influence the physiological demands of a given training load. Further investigation is needed to clarify the hormonal, biomechanical, and perceptual mechanisms underlying these phase-related differences and their implications for endurance performance.
References
1. Barnes KR, Kilding AE. Sports Med Open 2015;1:8.
2. McNulty KL, Elliott-Sale KJ, Dolan E, et al. Sports Med 2020;50:1813-1827.