An observational study in Low Energy Availability and Relative Energy Deficiency in Sport, sponsored by Bispebjerg Hospital. Recruiting at 1 site in Denmark. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-11-18.
Sponsored by Bispebjerg Hospital · Observational
This study investigates how energy availability affects performance, injury risk, and training outcomes in elite triathletes. Over two competitive seasons (2026-2027), 40 elite and sub-elite triathletes will be monitored through physiological tests, blood samples, and questionnaires. The goal is to identify markers of low energy availability and understand its impact on health and athletic performance. The study is observational and does not involve experimental treatments. Participants continue their regular training and diet while undergoing periodic assessments.
Low energy availability (LEA) is a condition where the energy intake of an athlete is insufficient to support both training demands and essential physiological functions. LEA is common among endurance athletes, including triathletes, due to high training volumes and sometimes intentional dietary restrictions. Prolonged LEA can lead to hormonal imbalances, impaired bone health, reduced immune function, and increased injury risk. This study aims to explore the prevalence and consequences of LEA in elite triathletes over two seasons.
The study is a 2-year exploratory cohort study conducted at the Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen. Forty elite or sub-elite triathletes (men and women, aged 18+) who train more than 15 hours per week will be enrolled. Participants will undergo five comprehensive test days spaced across the off-season, pre-season, and in-season periods of 2025-2027. These test days include blood sampling, DXA scans, MR imaging, muscle strength and stiffness assessments, VO₂ max testing, and dietary and activity monitoring.
The primary outcome is the change in the thyroid hormone triiodothyronine (T3), a known marker of LEA. Secondary outcomes include bone density, muscle mass, metabolic rate, performance metrics (e.g., running economy, VO₂ max), and injury incidence. Energy availability will be assessed via validated questionnaires (LEAF-Q for females, LEAM-Q for males), dietary logs (MyFood24), and training data from wearable devices.
Monthly injury reports and quarterly dietary assessments will be collected. Blood samples will be analyzed for hormones (e.g., cortisol, testosterone, GH, IGF-1, TSH, T3, T4), bone turnover markers (CTX, PINP, osteocalcin), immune parameters, and nutritional status (e.g., vitamin D, iron, B12). Some samples will be stored in a coded biobank until 2029 for future analysis.
Participants will receive no financial compensation but will be reimbursed for public transport. All procedures are non-invasive or minimally invasive and carry low risk. The study has been approved by the relevant ethics committee (Approval No. H-25043062), and informed consent will be obtained from all participants.
Results will be published in peer-reviewed journals and presented at scientific conferences. If not accepted for publication, results will be made publicly available via ClinicalTrials.gov and the EU Clinical Trials Register.
20 studies on the registry are indexed under Relative Energy Deficiency in Sport; 9 are open to participants now.
This study's planned enrollment of 40 is close to the median of 42 across 10 observational studies indexed under Relative Energy Deficiency in Sport.
Browse Relative Energy Deficiency in Sport studies →Bispebjerg Hospital is the lead sponsor of 289 studies on the registry; 29 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Elite triathletes with a weekly training volume of more than 15 hours
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Elite triathletes
T3
Plasma triiodothyronine (T3) levels
Time frame: Two years - from off-season 2025 until in-season 2027
RER
Resting energy expenditure by indirect calorimetry
Time frame: Two years - from off-season 2025 until in-season 2027
Bone mineral density
Bone mineral density by DXA scanning
Time frame: Two years - from off-season 2025 until in-season 2027
Fat free mass
Fat free mass by DXA scanning
Time frame: Two years - from off-season 2025 until in-season 2027
Appendicular fat free mass
Appendicular fat free mass by DXA scanning
Time frame: Two years - from off-season 2025 until in-season 2027
Fat mass
Fat mass by DXA scanning
Time frame: Two years - from off-season 2025 until in-season 2027
Tendon thickness
Patella and Achilles tendon thickness by ultrasound
Time frame: Two years - from off-season 2025 until in-season 2027
Tendon vascularisation
Color doppler by ultrasound of Patella and Achilles tendons
Time frame: Two years - from off-season 2025 until in-season 2027
Tendon stiffness
Patella and Achilles tendon stiffness by MyotonPro measurement
Time frame: Two years - from off-season 2025 until in-season 2027
Quadriceps muscle strength
Concentric muscle strength by Biodex dynamometer
Time frame: Two years - from off-season 2025 until in-season 2027
Hamstring muscle strength
Concentric muscle strength by Biodex dynamometer
Time frame: Two years - from off-season 2025 until in-season 2027
Peak muscle power
Measured during counter movement jump on force-plate
Time frame: Two years - from off-season 2025 until in-season 2027
Jump height
Measured during counter movement jump on force-plate
Time frame: Two years - from off-season 2025 until in-season 2027
Running economy
Measured on treadmill with direct measurement of oxygen uptake
Time frame: Two years - from off-season 2025 until in-season 2027
Biking economy
Measured on ergometer bike with direct measurement of oxygen uptake
Time frame: Two years - from off-season 2025 until in-season 2027
Maximal oxygen uptake
Measured on ergometer bike with direct measurement of oxygen uptake
Time frame: Two years - from off-season 2025 until in-season 2027
Calorie intake
Measured on three-day dietary registrations
Time frame: Two years - from off-season 2025 until in-season 2027
Exercise energy expenditure
Measured by tracking devices
Time frame: Two years - from off-season 2025 until in-season 2027
Risk of low energy availability
Evaluated by questionnaires - LEAF-Q for females, and LEAM-Q for males
Time frame: Two years - from off-season 2025 until in-season 2027
Risk of eating disorder
Evaluated by EDE-Q questionnaire
Time frame: Two years - from off-season 2025 until in-season 2027
Injury prevalence
Evaluated through monthly injury diary
Time frame: Two years - from off-season 2025 until in-season 2027
Time loss due to injuries
Evaluated through monthly injury diary
Time frame: Two years - from off-season 2025 until in-season 2027
Biomarkers
Biomarkers related to metabolism, stress hormones, sex hormones, immune system, muscle breakdown, organ function, bone turnover, lipid profile, minerals, haemoglobin and iron status measured from blood samples
Time frame: Two years - from off-season 2025 until in-season 2027
Plan to share: Undecided
Started Oct 2025 (actual). Primary completion is estimated for Nov 2027, 25 months after the start.
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