Reference · train by feel
RPE Scale: Train Without a Device
Rate of Perceived Exertion (RPE) lets you gauge intensity by feel. Two scales are common: Borg’s original 6–20 (it loosely tracks heart rate ×10) and the CR10 scale of 0–10. Map them to zones like this: CR10 3–4 (Borg 10–12) is easy Zone 2; CR10 7–8 (Borg 15–16) is threshold Zone 4.
| 5-Zone | CR10 | Borg 6–20 | How it feels | Polarized |
|---|---|---|---|---|
| Z1 · Recovery | 1–2 | 6–9 | Very easy; full conversation | Zone 1 (easy) |
| Z2 · Endurance | 3–4 | 10–12 | Easy; can talk in sentences | Zone 1 (easy) |
| Z3 · Tempo | 5–6 | 13–14 | Moderate; short sentences | Zone 2 (grey) |
| Z4 · Threshold | 7–8 | 15–16 | Hard; a few words only | Zone 3 (hard) |
| Z5 · VO₂max+ | 9–10 | 17–20 | Very hard to maximal; no talking | Zone 3 (hard) |
Borg 6–20 vs CR10
Gunnar Borg’s original RPE scale runs from 6 to 20 because it was designed so that multiplying by ten roughly approximates heart rate in beats per minute for a healthy adult (e.g. RPE 13 ≈ 130 bpm). The later category-ratio CR10 scale runs 0–10 and is more intuitive for non-linear sensations like breathlessness and muscle burn. Both are validated and widely used.
Why RPE still matters with a device
Heart rate lags effort and drifts in heat; power and pace don’t capture how fatigued you are today. RPE fills the gap. Strength training and CrossFit have no heart-rate anchor at all, so RPE (and velocity-based training) is the primary intensity gauge. Use the scale above to translate any session into the zone model you already train by.