HRV vs Resting HR: Which to Track?
Both heart rate variability and resting heart rate are useful recovery metrics but they measure different things and respond differently to stressors. I track both in FitPulse and have developed a rough interpretation framework over two years of data.
Resting HR is a lagging indicator. It reflects cumulative fatigue over days to weeks. A sustained elevation of 5+ bpm above baseline (measured over a 5-day rolling average) reliably predicts that I'm under-recovered. It's slow to respond to acute stressors like a single hard session.
HRV is a leading indicator. It reflects acute nervous system state — how well your autonomic balance recovered overnight. A single significantly low HRV reading (>20 ms below baseline RMSSD) suggests the previous day's stress (training, sleep, illness, travel) was not fully absorbed. Two consecutive low readings means I scale back the planned session.
Where they disagree is interesting. High resting HR with normal HRV: usually dehydration or caffeine timing. Low HRV with normal resting HR: often a sign of mental/life stress rather than training stress — the sympathetic nervous system is activated without the cardiovascular cost of exercise. In both cases FitPulse logs the outlier and I note the likely cause in the session journal.