🏋️ Athletic Performance & Recovery

What this panel can settle, and by what logic

Twelve markers, and the ones worth the money answer a question training data cannot: whether you are under-fueled, under-recovered or iron depleted.

1. Ferritin with the Iron Panel (Iron, TIBC, Transferrin Saturation) and Complete Blood Count (CBC) with Differential is the highest yield on the panel for endurance athletes. Exercise itself drives the iron problem: hepcidin rises after a hard session and restricts iron absorption for hours afterward, and baseline iron status changes the size of that response Peeling 2014. Depletion shows in ferritin long before hemoglobin moves Cancado 2025.
2. Free T3 (Triiodothyronine) with Total Testosterone and the Comprehensive Metabolic Panel (CMP) is the low-energy-availability signature. Relative energy deficiency in sport suppresses the reproductive and thyroid axes together, and the IOC consensus treats that pattern as the clinical entity rather than any single marker Mountjoy 2023.
3. hs-CRP (High-Sensitivity C-Reactive Protein) is a training-load reading, not a disease marker. Regular training lowers resting CRP — significant reductions appeared in 11 of 25 aerobic trials in one review Michigan 2011 — so a persistently raised value in a trained athlete is a question about recovery, illness or something else entirely.
4. Cortisol (AM) before 9am and IGF-1 (Insulin-like Growth Factor 1) add context at the edges. IGF-1 falls with sustained energy restriction and is the nutritional half of what the growth-hormone axis reports Yuen 2023.

What it cannot settle, and what would

There is no blood test for overtraining syndrome. The diagnosis is made on performance decrement that persists through adequate rest, and a review of biomarkers proposed for relative energy deficiency in sport found no single marker validated to make the call Dvořáková 2024. Twelve normal results in an athlete who is slowing down do not mean the athlete is fine.

It cannot measure bone, which is the outcome that ends careers. Low energy availability damages bone before it changes any hormone you can afford to measure repeatedly, and the assessment is DEXA with a fracture history Mountjoy 2023.

It cannot measure energy availability, and that is the actual variable. Energy availability is intake minus exercise energy expenditure relative to fat-free mass — a calculation from food and training records, not a marker Mountjoy 2023.

And it cannot tell you anything about performance. VO2max, lactate threshold, critical power and economy are measured on a bike or a treadmill. A raised IGF-1 (Insulin-like Growth Factor 1) is not a fitness score, and IGF-1 alone is a poor test of the growth-hormone axis in any direction Yuen 2023.

Draw conditions that decide whether the money is wasted

More of this panel is destroyed by the previous 72 hours than by anything you eat, which is why the training log matters more than the fast.

1. At least 48 hours, preferably 72, after a hard session. Strenuous exercise provokes an acute-phase response that raises hs-CRP (High-Sensitivity C-Reactive Protein) and Ferritin together Michigan 2011 Luo 2023, and post-exercise hepcidin shifts the iron picture on top of that Peeling 2014. Draw the day after a long run and you get an inflamed athlete with iron that looks better than it is — both errors in the wrong direction at once.
2. Cortisol (AM) before 9am or not at all. The morning reference interval is the only one that exists, and attempts to build usable afternoon thresholds show why the substitution fails Ramadoss 2021.
3. Fasted, and after a normal eating day. A deliberately light day before the draw lowers Free T3 (Triiodothyronine) and IGF-1 (Insulin-like Growth Factor 1), which is the signal this panel is meant to detect Mountjoy 2023 Yuen 2023.
4. Record altitude, heat and any recent blood donation. All three move the Complete Blood Count (CBC) with Differential independently of training, and a hematocrit read without that context is a misleading number.

How you would know it answered your question, and what each pattern means next

Five patterns, and the intervals below are set by iron kinetics and by how long a fueling change takes to register.

• Ferritin under 30 ng/mL, or under 50 with unexplained fatigue in an endurance athlete: treat and retest at 12 weeks. Take iron in the morning and away from training, since post-exercise hepcidin blocks absorption for hours Peeling 2014 Cancado 2025.
• Low Free T3 (Triiodothyronine) with low Total Testosterone and a low IGF-1 (Insulin-like Growth Factor 1): read it as under-fueling until proved otherwise. Restore energy availability and repeat at 12 weeks, which is the earliest the axes reliably recover Mountjoy 2023 Dvořáková 2024.
• hs-CRP (High-Sensitivity C-Reactive Protein) above 3 mg/L on a properly rested draw: repeat in 4 weeks after a genuine deload. If it stays up, this is a medical question rather than a training one Michigan 2011.
• Low morning Cortisol (AM): not a training finding. Add ACTH (Adrenocorticotropic Hormone) and see a clinician Ramadoss 2021.
• Everything normal and performance still falling: the panel has excluded the measurable causes. Audit sleep, energy intake and training load, and get a bone assessment if you are amenorrheic or have had a stress fracture Mountjoy 2023.

Sources read for these sections

• Peeling P, et al. Iron status and the acute post-exercise hepcidin response in athletes. PLoS One 2014 · PMID 24667393
• Michigan A, Johnson TV, Master VA. Review of the relationship between C-reactive protein and exercise. Molecular Diagnosis and Therapy 2011 · PMID 22047154
• Mountjoy M, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine 2023 · PMID 37752011
• Dvořáková K, et al. A literature review of biomarkers used for diagnosis of relative energy deficiency in sport. Frontiers in Sports and Active Living 2024 · PMID 39070233
• Ramadoss V, et al. Improving the Interpretation of Afternoon Cortisol Levels and SSTs to Prevent Misdiagnosis of Adrenal Insufficiency. Journal of the Endocrine Society 2021 · PMID 34611573
• Yuen KCJ, et al. Diagnosis and testing for growth hormone deficiency (GHD) across the ages: a global view of the accuracy, caveats and cut-offs for diagnosis. Endocrine Connections 2023 · PMID 37052176
• Cancado RD. Defining Global Thresholds for Serum Ferritin: A Challenging Mission in Establishing the Iron Deficiency Diagnosis in This Era of Striving for Health Equity. Diagnostics (Basel) 2025 · PMID 39941219
• Luo H, et al. A Practical Guide to Adjust Micronutrient Biomarkers for Inflammation Using the BRINDA Method. Journal of Nutrition 2023 · PMID 36792034