Heart rate monitors crash. Power meters drift. GPS cuts out in tunnels. But RPE - Rate of Perceived Exertion - always works.
Here's how to use it properly, and how to combine it with objective data for better training.
The Borg scale (simplified)
| RPE | Description | What it feels like | |---|---|---| | 1–2 | Very light | Walking, easy spinning | | 3–4 | Light | Zone 1–2 endurance pace | | 5–6 | Moderate | Zone 3 tempo - can talk in sentences | | 7–8 | Hard | Zone 4 threshold - can talk in words | | 9 | Very hard | VO₂max intervals - can't talk | | 10 | Maximal | Sprint, absolute limit |
Most endurance training should be at RPE 3–5 (easy-to-moderate). Twice a week, go to RPE 7–9 for intervals.
When RPE beats data
1. You're fatigued or sick
Your normal Z2 heart rate might be 135 bpm, but when you're fighting a cold or deeply fatigued, that same effort might spike to 145+. Your power meter says you're in Z2. Your body says otherwise. Trust RPE.
2. Heat, altitude, or humidity
Your power and heart rate shift in hot weather or at altitude. RPE is the only metric that adjusts automatically. If your normal tempo pace feels like threshold effort in 35°C heat - it is threshold effort. Train accordingly.
3. Caffeine and medication
Caffeine elevates heart rate. Beta-blockers suppress it. Neither changes your actual effort level. If you've just had a double espresso, your HR zones are wrong. RPE is right.
4. Indoor vs outdoor
Most people produce less power indoors than outdoors at the same perceived effort (partly cooling, partly psychology). If your indoor "Z3" feels like Z4 outdoors… it probably is. RPE bridges the gap.
How to combine RPE with data
The most effective approach is neither "trust all data" nor "ignore data and trust feel" - it's cross-reference them.
After each session, note your session RPE (1–10) alongside the objective numbers. Over time, you'll see patterns:
- When RPE is high but power is low → you're fatigued (back off)
- When power is high but RPE is low → you're peaking (race ready)
- When HRV is low and RPE for the same workout is elevated → early illness detection
Baseline shows your training load, recovery metrics, and performance trends in one place. The AI insights card surfaces the correlations so you don't have to hunt for them manually.
The best athletes I know have a simple heuristic: train by power/pace, race by RPE, recover by HRV.
Data guides the training plan. Subjective feel guides the execution. Recovery metrics confirm you got it right.