Free T3 in ketogenic athletes Low-normal Free T3 with normal TSH is common on LCHF diets, reflecting reduced peripheral T4→T3 conversion — the "low T3 syndrome" of energy restriction. This is a metabolic adaptation distinct from primary hypothyroidism. Ensure adequate energy availability before attributing to dietary pattern.

CK Interpretation <250: recovered · 250–500: mild damage · 500–2000: moderate (avoid eccentric ≥48h) · >2000: severe, rest · >5000: rhabdomyolysis risk, urgent review.

Ferritin Note Lab normal range (15–300 ng/mL) is misleading for athletes. Values <35 ng/mL impair VO₂max and endurance performance even without frank anaemia. Hepcidin-mediated absorption impairment and foot-strike haemolysis increase requirements in endurance athletes.

PURE Study (Leong 2015, n=139,691) Each 5kg reduction in grip strength associates with 17% increased cardiovascular mortality — a stronger predictor than systolic blood pressure. Gait speed <0.8m/s meets the EWGSOP2 severe sarcopenia threshold.

RBC Magnesium — Critical Note Serum magnesium reflects only 1% of total body magnesium and is an unreliable proxy. Always request RBC (not serum) Mg specifically. Deficiency is common in endurance athletes (sweat losses), LCHF dieters, and chronically stressed individuals — directly impairing HRV, sleep architecture, testosterone synthesis, and neuromuscular function. All are primary PRISM domains.

Gut–Exercise Axis Intensive exercise induces intestinal permeability via splanchnic vasoconstriction and tight junction disruption — bacterial LPS translocates into circulation, activating TLR4 and generating IL-6, TNF-alpha, and CRP already measured in Domain 1. Athletes with compromised gut barrier produce disproportionate inflammatory responses to equivalent training loads. Sample zonulin ≥48h post-exercise. Calprotectin >200 μg/g warrants gastroenterology referral.