HRV, in a nutshell
Heart rate variability (HRV) measures the micro-variations in time between two beats. Counter-intuitive but well-established : a well-recovered heart beats slightly irregularly — that's the sign of a relaxed nervous system, ready to take a hit. When fatigue or stress build up, HRV tends to drop.
Three windows onto the same state
Baseload reads what your watch or sensor sends to Apple Health — Baseload measures nothing itself:
- HRV : the balance of your autonomic nervous system.
- Resting heart rate : tends to rise when you're tired, coming down with something, or in sleep debt.
- Sleep : the primary raw material of recovery.
Cross-referenced, these signals feed a recovery "battery" — a percentage of energy remaining, also tracked per muscle group (see multi-sport).
Baseload reads a trend over several days, never a single isolated value. A low HRV on one morning means almost nothing — a short night, one drink too many, some stress are enough. An HRV that drops three days in a row, that's a signal. It's that slope the coach watches, not today's number.
What it changes in practice
When your recovery slips while a hard session is planned, the coach tells you plainly and offers an explainable alternative. For example: "Your HRV has dropped 15% over 3 days, so I'm suggesting a Z2 session instead of the planned intervals." You always stay in control — it's a reasoned proposal, not an order.
HRV is highly individual and noisy. Its absolute value can't be compared from one person to another, and it depends on how your watch measures it. It's not a diagnostic tool : a persistent drop can come from training or from something else. Baseload uses it as a trend signal among others, not as a health verdict. See Our model, its limits.