RPE vs Heart Rate: Which One Should You Trust?
Heart rate lies on hot days. RPE lies when you're motivated. Here's how to use both — and when each one wins.
Rate of Perceived Exertion (RPE) is a 1–10 scale of how hard a session feels. It's the oldest pacing tool in endurance sport, and still one of the best — because it's the only metric that includes everything your body knows about itself.
When heart rate wins
On controlled, steady runs at sea level in cool weather, HR is reliable and objective. It catches creeping fatigue before you feel it.
When RPE wins
Heat, humidity, altitude, dehydration, caffeine, and stress all push HR up at the same effort. On those days, RPE is the more honest target — and it's the only signal that works for short intervals where HR lags.
The best athletes use both. The best coaches teach you when to listen to which.
The KYN approach
Every KYN workout is prescribed in both. Tap the toggle to switch the whole plan between zones and RPE — useful when you're travelling, racing, or running without a chest strap.