Table 1

Overview of study specific aims, samples and data sources

Studies, samples, and purposesTime frameSelf-report instrumentsMicrotecnological devicesBiological measures
Study 1 (n=13)
Aim: To evaluate the accuracy of methods measuring exercise energy expenditure (EE) against the gold standard of indirect calorimetry.
March–April 2021.
Baseline +7 days consequtively
RPEGPS-tracking, foot mounted accelerometer/ gyroscope
Vo2 (indirect calorimetry)
Blood lactate (mmol/L)
Study 2 (n=20)
Aim: To quantify energy intake (EI), EE and its implications for nutritional recommendations
September 2021–April 2022. Baseline +14 days consequtively24 hours diet recall × 3.
Weekly weight measurement.
GPS tracking
Activity monitor with integrated accelerometer
Study 3 (n=50)
Aim: To identify the point prevalence of LEA and validity of subjective measure of LEA through objective physiological markers
September 2021–April 2022.
Baseline +30 days
LEAF-Q +additional items
EDE-Q core items.
EI (food registration) and training intensity on food registration days
Analysis of the following biochemical markers:
TSH, free T3 free T4, glucose, insulin, C-peptide, cortisol, S-CTX-1 (collagen I), PINP, leptin, adiponectin, IGF-1, IGFBP3, estradiol, testosterone and SHBG.
Serum and plasma collection for biobanking.
Transvaginal Ultrasound (If indicated by testosterone levels)
Study 4 (n=50)
Aim: To explore whether the prevalence of LEA varies across a full football season and its possible biological and psychological covariates
January 2022–January 2023.
1 year (four measure points during 3–5 testing days at baseline, in season, and post-season, respectively)
LEAF-Q +additional items
EDE-Q core items
CFQ (fatigue)
GHQ-12 (mental distress)
BIS (insomnia)
SoC-13 (resilience)
QoL-BREF (well-being)
See study 3. A selection will be made based on study 3-findings for a subsample (N=20).
Physical performance (baseline and post season).
  • BIS, Bergen Insomnia Scale; CFQ, Chalder Fatigue Scale; CTX-1, type I collagen cross-linked C-telopeptide; DLW, double labelled water; DXA, dual-X-ray-absorptiometry; EDE-Q, Eating Disorder Examination Questionnaire; GHQ-12, General Health Questionnaire-12; LEA, low energy availability; LEAF-Q, Low Energy Availability in Females Questionnaire; PINP, Procollagen type I N-terminal propeptide; RMR, resting metabolic rate; RPE, Rated Perceived Exertion; SoC-13, Sense of Coherence Scale; TSH, thyroid stimulating hormone; VO2, oxygen uptake.