Table 1.
Overview of study specific aims, samples and data sources
| Studies, samples, and purposes | Time frame | Self-report instruments | Microtecnological devices | Biological 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 |
RPE | GPS-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 consequtively | 24 hours diet recall × 3. Weekly weight measurement. |
GPS tracking Activity monitor with integrated accelerometer |
DLW and DXA |
| 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 |
DLW RMR DXA 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) |
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| 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.