Altitude Training Effectiveness; Is There a Role for Sleep and Menstrual Health? (FEMHEALTH)

January 6, 2026 updated by: Bart Roelands, Vrije Universiteit Brussel
Therefore, the present study aims to evaluate the role of the impact of altitude on sleep and the menstrual cycle in the inter- and intraindividual variability of altitude training effectiveness. In order to do so, elite female cyclists will be monitored before, during and after an altitude training camp. The monitoring will include menstrual cycle characteristics, sleep and altitude effectiveness and will start three months before the start of the altitude training camp and end two months after the altitude training camp. Both naturally cycling women and women using contraceptives will be included in the study. Menstrual cycle monitoring will take place via self-reports and via a daily saliva (Eli Health) and urine (Proov) test to measure progesterone concentration. Besides proges-terone concentration, the sampled urine will also be used to perform an ovulation test on (i.e., measuring the luteinizing hormone). In addition, a blood sample will be collected at the start of each menstrual cycle to evaluate the concentration of menstrual cycle-related hormones (e.g., fol-licle-stimulating hormone, luteinizing hormone, estrogen, and progesterone) and to evaluate the functioning of the Hypothalamic-Pituitary-Adrenal Axis (i.e., cortisol concentration). Sleep moni-toring will be performed via the use of questionnaires, actigraphy and polysomnography. Lastly, altitude effectiveness will be evaluated via the altitude-associated response in total hemoglobin mass and via an all out cycle ergometer task.

Study Overview

Status

Not yet recruiting

Conditions

Detailed Description

Elite athletes are constantly aiming to improve their performance and, eventually, outperform their opponents. In this endeavor, various methods have been designed to gain an advantage over the other competitors. One of those methods, which has been in use for quite some time and remains very popular, is altitude training. Currently, multiple protocols of altitude training have been developed. A general distinction can be made between "live high, train high" (LHTH), "live high, train low" (LHTL), and "live low, train high" (LLTH) altitude training. The LHTL protocol is cur-rently being put forward as the most effective one for training gains.

The overall effectiveness of altitude training to improve performance is backed up by a significant amount of scientific data. Nonetheless, up to date, the efficacy of altitude training is still questioned by some, due the lack of rigorous and well-controlled investigations, and no scientific consensus exists. Since Lundby and colleagues published their critical views on the general application of altitude training to enhance performance in elite athletes, follow-up research has substantiated these critical views of Lundby and colleagues. Nevertheless, the debate on the usefulness of altitude training in elite athletes is still ongoing, and currently revolves around whether athletes with an already high hemoglobin mass (i.e., elite athletes) can successfully increase their hemoglobin mass via altitude training.

A topic that could provide some new insights is the issue of intra- and interindividual variability in the response to altitude training, and the underlying mechanisms of these variabilities. Multiple studies have been performed that clearly outline the presence of both intra- and interindividual variability in the response to altitude training. The determination and evaluation of all state and trait-specific factors that could influence an athlete's response to altitude training is cur-rently ongoing. Nummela et al. showed that the mean effectiveness of altitude training in yielding an increase in hemoglobin mass could rise from 56% to 69% when targeting altitude exposure (2,000-2,500 m), iron deficiency and inflammation as moderating state factors. This emphasizes the need to carefully consider all the possible moderating state factors that may influence an athlete's response to altitude training. Furthermore, these findings stress the need for future research to describe more accurately how these different influencing state factors (and potential oth-er state and trait factors) interact to impact the altitude training-response in both elite and recrea-tional athletes.

One of these potentially crucial factors that could play a role in the effectiveness of altitude training to trigger performance-improving adaptations is sleep. Sleep is one of the most important aspects of recovery, and nowadays it is recommended to stay below 3,000 m (or an equivalent normobaric reduction of inspired O2) at night in altitude training paradigms. This recommendation is based on the fact that sleep is impaired at high altitude, and impaired sleep could counteract the positive physiological responses that are aimed for, certainly when it is prolonged for ~2-3 weeks (i.e., the current suggested optimal hypoxic dose, taking into account altitude and exposure time [1]). However, the guideline to stay below 3,000 m to prevent altitude-induced sleep impairments might be inadequate. Hoshikawa et al. demonstrated that acute exposure to normobaric hypoxia equivalent to a 2,000 m altitude decreased slow-wave sleep in athletes, but it did not change subjective sleepiness or amounts of urinary catecholamines. These results point out that the athlete's sleep might be disturbed even at moderate altitudes of 2,000 m and, more importantly, that athletes are not aware of it (i.e., subjective sleepiness did not change). Moreover, the study of Hoshikawa et al. also revealed that the apnea/hypopnea index (AHI; i.e., the number of signif-icant respiratory events qualifying as apnea or hypopnea per hour of sleep) increased in hypoxia compared to normoxia, and the magnitude of this effect varied widely among participants (i.e., high interindividual variability). This high interindividual variability might be associated with the interindividual variability that is observed in altitude training effectiveness. A hypothesis that is further substantiated by the recently published data of Mujika et al., that demonstrates a link between subjective sleep quality and the effectiveness of altitude training to increase total hemo-globin mass.

Specifically within female athletes, another potential crucial factor in the effectiveness of altitude training is the hypothalamic-pituitary-ovarian (HPO) axis function. The hypothalamic-pituitary-ovarian (HPO) axis regulates reproductive function, including the orchestration of ovula-tion and menstrual cyclicity. HPO axis suppression leads to altered hormonal patterns and conse-quently short luteal phases, anovulation and amenorrhoea. Shaw et al. concluded in their sys-tematic review that, if lowlanders travel to highland for short or longer duration, the high altitude-hypoxia affects their menstrual cycle more adversely than the natives. The variation in female hormones may contribute in unsuccessful ovulation, menstrual cycle, and subsequently pregnancy at high altitude. A disturbed HPO axis function at altitude can, subsequently, negatively im-pact the effectiveness of altitude training. For example, Heikura et al. recently reported lower pre-hypoxic exposure hemoglobin mass levels in amenorrheic versus eumenorrheic women, sug-gesting that menstrual dysfunction, an indicator of long-term low energy availability, may influence the altitude exposure-related increase in hemoglobin mass or its magnitude.

Therefore, the present study aims to evaluate the role of the impact of altitude on sleep and the menstrual cycle in the inter- and intraindividual variability of altitude training effectiveness. In order to do so, elite female cyclists will be monitored before, during and after an altitude training camp. The monitoring will include menstrual cycle characteristics, sleep and altitude effectiveness and will start three months before the start of the altitude training camp and end two months after the altitude training camp. Both naturally cycling women and women using contraceptives will be included in the study. Menstrual cycle monitoring will take place via self-reports and via a daily saliva (Eli Health) and urine (Proov) test to measure progesterone concentration. Besides proges-terone concentration, the sampled urine will also be used to perform an ovulation test on (i.e., measuring the luteinizing hormone). In addition, a blood sample will be collected at the start of each menstrual cycle to evaluate the concentration of menstrual cycle-related hormones (e.g., follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone) and to evaluate the functioning of the Hypothalamic-Pituitary-Adrenal Axis (i.e., cortisol concentration). Sleep monitoring will be performed via the use of questionnaires, actigraphy and polysomnography. Lastly, altitude effectiveness will be evaluated via the altitude-associated response in total hemoglobin mass and via an all out cycle ergometer task.

Study Type

Observational

Enrollment (Estimated)

30

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

Eligibility criteria are being a healthy female elite cyclist. Both naturally cycling women and women who use contraception are eligible.

Description

Inclusion Criteria:

  • Healthy
  • Female
  • Elite cyclist

Exclusion Criteria:

-

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Elite female cyclists
Elite female cyclists participating in an altitude training camp

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Total hemoglobin mass (tHBmass)
Time Frame: Will be measured at sea level 5 days before (i.e., Day -5) and on the last day of the altitude training camp (i.e., Day 18)
An optimized carbon monoxide rebreathing method will be used. The carbon monoxide dose will be 0.8 mL/kg body mass. The rebreathing procedure will be performed for 2 minutes, in a seated position, through a glass spirometer.
Will be measured at sea level 5 days before (i.e., Day -5) and on the last day of the altitude training camp (i.e., Day 18)
A standardized 5-min all-out cycling test
Time Frame: Will be performed on a calibrated cycle ergometer 5 days before (i.e. Day -5) and on the final day of the altitude training camp (i.e., Day 18)
After a 10-15 min warm-up, participants will complete a maximal 5-min effort in linear (cadence-dependent) mode, during which they will be instructed to produce the highest sustainable power for the entire duration. Power output, cadence, and heart rate will be recorded continuously. Mean 5-min power (W and W·kg-¹) will serve as the primary performance outcome, with peak power and end-segment power examined as secondary metrics.
Will be performed on a calibrated cycle ergometer 5 days before (i.e. Day -5) and on the final day of the altitude training camp (i.e., Day 18)
A wake and sleep diary
Time Frame: Participants will have to fill out this wake and sleep diary daily from Day -7 to Day 25 (Day 0 being the first day of the altitude training camp).
Will be used regarding sleep (completed by participants the morning upon waking) and daytime activity (completed prior to their bedtime). The participants have to indicate, on a 24-h scale with a time resolution of 15 min, 1) when they started trying to fall asleep, 2) when they actually fell asleep, 3) whether they woke up after falling asleep and, if yes, for how long, 4) when they woke up, and 5) whether they took a nap out of bed and, if yes, for how long. Subsequently, the following outcome measures will be calculated: total time spent in bed, sleep onset latency, wake after sleep onset, total sleep time, total nap time, bed-time and risetime. In addition, participants will also be asked to rate their sleep quality, quality of the wake-up and shape of the day (score on a 10-point scale).
Participants will have to fill out this wake and sleep diary daily from Day -7 to Day 25 (Day 0 being the first day of the altitude training camp).
The Pittsburgh Sleep Quality Index (PSQI)
Time Frame: The PSQI will have to be completed at the end of each month in which the menstrual cyclus is monitored (i.e., Month -3 final day, Month -2 final day, Month -1 final day, Month 0 final day, Month 1 final day and Month 2 final day).
The PSQI includes 19 self-assessment items that combine to give 7 components of the overall score, with each component receiving a score of 0 to 3. A score of 0 indicates no difficulty, while a score of 3 indicates severe difficulty. The 7 components of the score add up to give an overall score ranging from 0 to 21 points, with 0 indicating no difficulty and 21 indicating major difficul-ties. An overall sum of 5 or more indicates a 'bad' sleeper.
The PSQI will have to be completed at the end of each month in which the menstrual cyclus is monitored (i.e., Month -3 final day, Month -2 final day, Month -1 final day, Month 0 final day, Month 1 final day and Month 2 final day).
Actigraphy
Time Frame: The participants will be requested to wear the ActiGraph for a period of 24 hours without interruption on Day -7, Day -6, Day 0, Day 1, Day 6, Day 7, Day 12, Day 13, Day 17, Day 18, Day 24 en Day 25 (Day 0 being the start of the altitude training camp).
Sleep measures will be assessed by non-dominant wrist-worn actigraphy with the ActiGraph wGT3X-BT device from Ametris and data will be collected with a sampling frequency of 30-50hz. The ActiGraph output variables will be total sleep time (TST, in min), total time in bed (TTB, in min), sleep onset latency (SOL, in min), wake after sleep onset (WASO, in min), number of awak-ening after sleep onset (nAw, number) and sleep efficiency (SE in %, the ratio between total sleep time and total time spent in bed) in agreement with the guidelines of the Society of Behavioral Sleep Medicine.
The participants will be requested to wear the ActiGraph for a period of 24 hours without interruption on Day -7, Day -6, Day 0, Day 1, Day 6, Day 7, Day 12, Day 13, Day 17, Day 18, Day 24 en Day 25 (Day 0 being the start of the altitude training camp).
Polysomnography
Time Frame: Will be used to monitor sleep on pre Day -7, Day -7, Day 1, Day 6, Day 12, Day 18 en Day 25 (Day 0 being the start of altitude training camp).
The SomnoTouch RESP system (SomnoMedics GmbH, Germany), a portable, Type III sleep diagnostic device will be used to perform ambulatory polysomnography. The device records respiratory effort, nasal airflow, blood oxygen saturation, heart rate, actigraphy, body position, and bilateral thoracic bio-impedance signals. Data will be collected in accordance with manufacturer specifications and validated scoring standards.
Will be used to monitor sleep on pre Day -7, Day -7, Day 1, Day 6, Day 12, Day 18 en Day 25 (Day 0 being the start of altitude training camp).
A survey which documents menstrual cycle history
Time Frame: Once, at the start of the monitoring period, 3 months prior the altitude training camp.
Any current or previous hormonal contraception use (type, formulation), the length and frequency of their menstrual cycle (including determination of any primary and secondary amenorrhea) and prevalence of known menstrual diagnoses (e.g., polycystic ovary syndrome [PCOS], endometriosis) will be documented.
Once, at the start of the monitoring period, 3 months prior the altitude training camp.
A short questionnaire asking whether they bled, flow and cramping.
Time Frame: On a daily basis. This daily basis monitoring will start three months before the start of the altitude training camp, and will end two months after the altitude training camp.
A short questionnaire asking whether they bled (+ form of bleeding; withdrawal, breakthrough or spotting bleeding), flow (light/medium/heavy) and cramping (0-10).
On a daily basis. This daily basis monitoring will start three months before the start of the altitude training camp, and will end two months after the altitude training camp.
A saliva (Eli Health) test
Time Frame: This daily testing will start 3 months before the start of the altitude training camp and end two months after the altitude training camp.
To measure progesterone concentration
This daily testing will start 3 months before the start of the altitude training camp and end two months after the altitude training camp.
A urine (Proov) test
Time Frame: This daily testing will start 3 months before the start of the altitude training camp and end two months after the altitude training camp.
To measure progesterone concentration
This daily testing will start 3 months before the start of the altitude training camp and end two months after the altitude training camp.
A urine sample
Time Frame: The ovulation test will have to be performed starting several days before the expected luteinizing hormone surge so that the peak is not missed (i.e., Day 7 of the cycle) and stop on Day 18 of the cycle (each cycle is 28 days).
To perform an ovulation test on (i.e., measuring the luteinizing hormone).
The ovulation test will have to be performed starting several days before the expected luteinizing hormone surge so that the peak is not missed (i.e., Day 7 of the cycle) and stop on Day 18 of the cycle (each cycle is 28 days).
A blood sample
Time Frame: At the start of each menstrual cycle during the monitoring period (from three months before the altitude training camp till two months after the altitude training camp).
To evaluate the concentration of menstrual cycle-related hormones (e.g., follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone) and to evaluate the functioning of the Hy-pothalamic-Pituitary-Adrenal Axis (i.e., cortisol concentration).
At the start of each menstrual cycle during the monitoring period (from three months before the altitude training camp till two months after the altitude training camp).

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Vrije Universiteit Brussel

Collaborators

Royal Military Academy

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

February 1, 2026

Primary Completion (Estimated)

June 1, 2026

Study Completion (Estimated)

June 1, 2026

Study Registration Dates

First Submitted

November 28, 2025

First Submitted That Met QC Criteria

January 6, 2026

First Posted (Actual)

January 13, 2026

Study Record Updates

Last Update Posted (Actual)

January 13, 2026

Last Update Submitted That Met QC Criteria

January 6, 2026

Last Verified

November 1, 2025

More Information

Terms related to this study

Other Study ID Numbers

  • FEMHEALTH

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Given that we will be working with elite cyclists, the IPD will be confidential.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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