Heart rate variability (HRV) measures the variation in milliseconds between successive heartbeats. Higher HRV generally indicates better recovery, lower stress and higher readiness to train hard. Lower HRV signals accumulated fatigue, illness or high stress. HRV is tracked daily by wearables like WHOOP and Garmin watches. Training should be lighter when HRV is suppressed and can be harder when HRV is elevated relative to your baseline. Individual baselines vary enormously — only your own trends matter, not comparisons to others.
Key points
- Variation between heartbeats in milliseconds
- Higher HRV = better recovery generally
- Lower HRV = fatigue, illness or stress signal
- Track daily trends, not absolute numbers