HRV for Runners: How to Actually Use It

HRV is the variation in time between successive heartbeats. A more recovered, parasympathetic-dominant body produces more variation. A stressed, fatigued, sympathetic-dominant body produces less. That much is true.

What HRV does well

• Confirms a hard week is genuinely hard — the trend drops.
• Flags accumulated fatigue early — 7 days below baseline is a real signal.
• Catches illness 24–48 hours before symptoms appear.

What HRV does poorly

• Single-day numbers are noisy. Coffee, alcohol, a late meal — all swing them.
• Comparing your HRV to a friend's is meaningless. It is highly individual.
• Telling you a hard session was good or bad — that is what RPE and HR drift are for.