The physiological signatures of low energy availability show up in HRV, resting heart rate, sleep, body mass, and menstrual function. Each signal is real and each has significant limits.
Relative Energy Deficiency in Sport (RED-S) explained in plain language — the body systems it affects, who is at risk, what diagnosis actually involves, and why wearables cannot detect it.
Energy availability, RED-S risk factors, biomarker signatures of underfueling, and the confounders that mimic them — plus where data stops and clinical assessment begins.