AUTHORS: Madison Taylor1, Maria Hrozanova2, Øyvind Sandbakk1,2, Boye Welde, John O. Osborne1, Dionne A. Noordhof2

1. School of Sport Sciences, UiT, The Arctic University of Norway, Tromsø, Norway

2. Department of Neuromedicine and Movement Science, Centre for Elite Sports Research, Norwegian University of Science and Technology, Trondheim, Norway

PURPOSE: The current study was part of the Female Endurance Athlete (FENDURA) project. This study investigated the influence of menstrual cycle (MC) phase on objective and subjective variables of sleep and recovery following standardized endurance-training sessions in endurance-trained women. 

METHODS: Over two MCs, 15 eumenorrheic endurance-trained women completed standardized low- (LIT) and high-intensity (HIT) endurance-training sessions during three distinct MC phases; 1) the early follicular phase (EFP), 2) the ovulatory phase (OP), and 3) the mid-luteal phase (MLP). Session type (HIT or LIT) was randomized such that participants completed LIT sessions during one MC and HIT sessions in the other MC. Phases were determined using calendar-based counting and at-home urinary ovulation tests, and retrospectively verified from serum estrogen and progesterone concentrations on each test day. Sleep was monitored with Somnofy, a validated non-contact sleep monitor, on the night of each training session. Subjective recovery was assessed 24 h post-session using a two-part questionnaire consisting of the Perceived Recovery Scale (single item) and Hooper Questionnaire (sleep quality, fatigue, stress, muscle soreness). Data were analyzed using random-intercept linear regression in R. 

RESULTS: MC phase had a main effect on time awake after sleep onset (WASO) (p<0.001), sleep efficiency (SE) (p=0.033), and the percentage of total sleep time spent in light sleep (p=0.023) and deep sleep (p=0.045). WASO increased by 12 and 19 min in MLP compared to EFP and OP respectively (p=0.043, p=0.001) along with a 3.5% decline in SE in MLP compared to OP (p=0.047). Light sleep increased from EFP to MLP (+5.1%, p=0.037), and an indication of reduced deep sleep in MLP was observed but did not reach statistical significance (-2.8%, p=0.074). There was no effect of MC phase on total sleep time (p>0.05) nor perceived sleep quality (p>0.05). No subjective recovery variables were influenced by MC phase, but perceived recovery was reduced following HIT compared to LIT (-1.27 points, p<0.001). No significant MC phase by session type interactions were observed. 

CONCLUSION: Menstrual cycle phase had a significant influence on multiple objective sleep variables, with indications of reduced sleep quality in MLP compared to the other phases, despite no change in subjective sleep quality. Neither objective nor subjective sleep quality were influenced by the type of training session. Perceived recovery was reduced following HIT- compared to LIT-sessions but was not influenced by MC phase.