Energy Availability and Its Impact in Elite Triathletes (TriatLEA)

Energy Availability in Elite Triathletes: Impact on Performance and Injury Risk

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.

Study Overview

• Status: Recruiting
• Conditions: Relative Energy Deficiency in Sport; Low Energy Availability

Detailed Description

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.

• Study Type: Observational
• Enrollment (Estimated): 40

Contacts and Locations

• Study Contact: Name: Jakob Agergaard, Ph.D.; Phone Number: +45 38 63 58 73; Email: jakob.agergaard@regionh.dk

Study Locations

• Denmark
  • Copenhagen, Denmark
    • Recruiting
    • Institute of Sports Medicine Copenhagen, Bispebjerg Hospital
    • Contact: Jakob Agergaard, Ph.D.; Phone Number: +45 38 63 58 73; Email: jakob.agergaard@regionh.dk

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Elite triathletes with a weekly training volume of more than 15 hours

Description

Inclusion Criteria:

• Age ≥18 years
• Healthy individuals
• Training ≥15 hours/week in triathlon

Exclusion Criteria:

• Smokers
• Use of prohibited substances (WADA list) without medical justification
• Existing injuries or illnesses that could worsen due to participation

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
Triathletes; Elite triathletes

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
T3	Plasma triiodothyronine (T3) levels	Two years - from off-season 2025 until in-season 2027

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
RER	Resting energy expenditure by indirect calorimetry	Two years - from off-season 2025 until in-season 2027
Bone mineral density	Bone mineral density by DXA scanning	Two years - from off-season 2025 until in-season 2027
Fat free mass	Fat free mass by DXA scanning	Two years - from off-season 2025 until in-season 2027
Appendicular fat free mass	Appendicular fat free mass by DXA scanning	Two years - from off-season 2025 until in-season 2027
Fat mass	Fat mass by DXA scanning	Two years - from off-season 2025 until in-season 2027
Tendon thickness	Patella and Achilles tendon thickness by ultrasound	Two years - from off-season 2025 until in-season 2027
Tendon vascularisation	Color doppler by ultrasound of Patella and Achilles tendons	Two years - from off-season 2025 until in-season 2027
Tendon stiffness	Patella and Achilles tendon stiffness by MyotonPro measurement	Two years - from off-season 2025 until in-season 2027
Quadriceps muscle strength	Concentric muscle strength by Biodex dynamometer	Two years - from off-season 2025 until in-season 2027
Hamstring muscle strength	Concentric muscle strength by Biodex dynamometer	Two years - from off-season 2025 until in-season 2027
Peak muscle power	Measured during counter movement jump on force-plate	Two years - from off-season 2025 until in-season 2027
Jump height	Measured during counter movement jump on force-plate	Two years - from off-season 2025 until in-season 2027
Running economy	Measured on treadmill with direct measurement of oxygen uptake	Two years - from off-season 2025 until in-season 2027
Biking economy	Measured on ergometer bike with direct measurement of oxygen uptake	Two years - from off-season 2025 until in-season 2027
Maximal oxygen uptake	Measured on ergometer bike with direct measurement of oxygen uptake	Two years - from off-season 2025 until in-season 2027
Calorie intake	Measured on three-day dietary registrations	Two years - from off-season 2025 until in-season 2027
Exercise energy expenditure	Measured by tracking devices	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	Two years - from off-season 2025 until in-season 2027
Risk of eating disorder	Evaluated by EDE-Q questionnaire	Two years - from off-season 2025 until in-season 2027
Injury prevalence	Evaluated through monthly injury diary	Two years - from off-season 2025 until in-season 2027
Time loss due to injuries	Evaluated through monthly injury diary	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	Two years - from off-season 2025 until in-season 2027

Collaborators and Investigators

• Sponsor: Bispebjerg Hospital

Publications and helpful links

Helpful Links

• Related Info

Study record dates

Study Major Dates

• Study Start (Actual): October 1, 2025
• Primary Completion (Estimated): November 30, 2027
• Study Completion (Estimated): June 1, 2028

Study Registration Dates

• First Submitted: November 14, 2025
• First Submitted That Met QC Criteria: November 14, 2025
• First Posted (Actual): November 18, 2025

Study Record Updates

• Last Update Posted (Actual): November 18, 2025
• Last Update Submitted That Met QC Criteria: November 14, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: biomarker; performance; triathlon; injury risk; RED-S
• Additional Relevant MeSH Terms: Mental Disorders; Feeding and Eating Disorders; Relative Energy Deficiency in Sport
• Other Study ID Numbers: BBH171; H-25043062 (Other Identifier: The Regional Health Research Ethics Committees for the Capital Region of Denmark)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No