Effects of the Menstrual Cycle and Oral Contraceptive Use on Health and Performance in Athletes

Condition(s) studied

Study summary

A review of the sports medicine literature reveals a clear underrepresentation of female athletes in research. In the current era of precision medicine, increasing attention has been directed toward the regulatory roles of estrogen and progesterone in athletic performance and health optimization. Regular fluctuations in estrogen and progesterone across menstrual cycle phases (i.e., early follicular, late follicular, and mid-luteal phases) may influence strength performance, hydration status, body composition, and energy balance. However, few studies have examined these outcomes using hormonal confirmation of menstrual cycle phases. Monophasic oral contraceptive use also represents a highly relevant hormonal condition among female athletes, as exogenous hormones suppress endogenous ovarian fluctuations and create distinct hormonal profiles across active pill-consumption and withdrawal phases. Nevertheless, the influence of oral contraceptive phases on strength-related outcomes, hydration markers, body water regulation, body composition, and energy balance remains insufficiently characterized, particularly in comparison with naturally menstruating athletes. In response to these gaps, this longitudinal observational study primarily aims to examine variations in strength-related outcomes across three distinct menstrual cycle phases (early follicular, late follicular, and mid-luteal) in eumenorrheic athletes. Secondary objectives include: (i) conducting within- and between-group comparisons of hydration status, energy balance, and strength outcomes (maximal, endurance, and explosive torque) in naturally menstruating athletes and oral contraceptive users; (ii) testing the reliability of methods used to assess body water, energy expenditure, and body composition across the menstrual cycle; (iii) exploring associations between energy availability, resting energy expenditure, and sex hormone concentrations across menstrual cycle phases; and (iv) testing, validating, and proposing methodological recommendations for the use of bioelectrical impedance analysis in tracking fluid-related changes across hormonal phases. To achieve these goals, the study will use a longitudinal observational design involving 40 female athletes, including 24 naturally menstruating athletes and 16 oral contraceptive users. Naturally menstruating athletes will be assessed during the early follicular, late follicular, and mid-luteal phases of the menstrual cycle, while oral contraceptive users will be assessed across pill-consumption and withdrawal phases. Measurements will be conducted across the three menstrual cycle phases and across oral contraceptive use phases, and will include: i) maximal voluntary isometric strength assessed using handgrip dynamometry, bench press, and leg press; ii) serum estrogen and progesterone; iii) body water and its compartments, and water turnover by dilution techniques; iv) hydration status by plasma osmolality, sodium, and vasopressin; v) energy balance by doubly labeled water and body composition changes; vi) resting energy expenditure by indirect calorimetry.

Eligibility

Primary outcome measure(s)

• Maximal Strength — 4 weeks
  Upper- and lower-body maximal strength will be assessed during the three evaluation periods using maximal voluntary isometric contractions performed on a bench press machine and a horizontal leg press, respectively. For each exercise, participants will perform three 5-second maximal voluntary isometric contractions, with 1-minute rest intervals between trials. All contractions will be executed isometrically, without joint movement. Maximal strength will be defined as the highest peak force value obtained during the maximal voluntary isometric contraction trials.
• Explosive Strength — 4 weeks
  Explosive strength of the upper and lower limbs will be assessed by analysing the rate of force development derived from the force-time curve obtained during maximal voluntary isometric contractions performed on a bench press machine (upper limbs) and a horizontal leg press (lower limbs). The rate of force development will be calculated as the slope of the force-time curve (Δforce/Δtime) and expressed in newtons per second (N/s). Peak rate of force development will be identified as the maximum slope of the force-time curve using a 20-millisecond sliding window. Sequential rate of force development will be computed over consecutive 50-millisecond intervals from contraction onset (0 ms) up to 250 ms. Values at 50, 100, 150, 200, and 250 ms will be reported in both absolute terms and normalised to maximal voluntary isometric contraction force, as previously described.
• Endurance Strength — 4 weeks
  Muscular endurance will be assessed for both upper and lower limbs using a bench press machine and a horizontal leg press, respectively. Participants will perform a sustained isometric contraction at 40% of their maximal voluntary isometric contraction force until task failure. Task failure will be defined as a force decline exceeding 10% below the target level (40% of maximal voluntary isometric contraction) sustained for more than 10 seconds. Standardised verbal encouragement and real-time visual feedback will be provided throughout the test.
• Handgrip strength — 4 weeks
  Handgrip strength will be measured as the maximal voluntary isometric contraction of the hand and forearm muscles using a portable hand dynamometer (JAMAR Plus+, Patterson Medical, USA). Participants will be assessed in a standing position with the arm in a neutral position (midway between supination and pronation) and the elbow fully extended alongside the body. Prior to testing, the dynamometer handle will be adjusted to each participant's hand size. Measurements will be performed alternately on both hands until three valid attempts are completed for each hand. For each attempt, the participant will exert maximal grip force for 5 seconds, followed by a 60-second rest interval.

Trial sites (1)

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