Number of heartbeats per minute. Normal resting range: 60–100 BPM. Below 60 is bradycardia; above 100 is tachycardia.

Breaths per minute. Normal adult range: 12–20 /min. Rises with stress or physical activity.

Percentage of oxygenated hemoglobin. Healthy adults typically ≥ 97%. Below 95% warrants medical attention. Note: rPPG-based SpO₂ is experimental.

Root mean square of successive IBI differences — measures autonomic nervous system flexibility. Higher = more relaxed. Typical range: 20–80ms; athletes may reach 100ms+.

Ratio of low-frequency to high-frequency HRV power. LF reflects sympathetic tone; HF reflects parasympathetic. Normal: 1–3. High (>3) suggests elevated sympathetic activity and stress.

Baevsky Stress Index — measures autonomic regulatory tension from IBI distribution. Reference: 20–150. Higher values indicate greater physiological stress burden.

Heuristic fatigue estimate combining HR and RMSSD. 0–30: relaxed, 30–60: moderate fatigue, 60–100: significant fatigue. ⚠ Heuristic — trend only.

Mental workload estimate from LF/HF and RMSSD — reflects current cognitive demand. 0–30: light, 30–60: moderate, 60–100: high load. ⚠ Heuristic — trend only.