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.
Session RPE vs interval RPE: why the distinction matters
The difference between session RPE (sRPE) and interval-specific RPE is one of the most underused but powerful distinctions in self-coached training. Session RPE is your overall rating of how hard the entire workout felt, including warmup, cooldown, and rest periods. You rate it 10-30 minutes after finishing, because rating mid-cooldown biases the score. The Borg session RPE protocol prescribes this delay specifically to let your body finish clearing metabolites before you assess.
Interval RPE captures the perceived intensity of individual work bouts: how hard did the fifth 800m repeat feel relative to the first? Were the last three threshold intervals equally hard, or did the final one feel harder at the same power?
This gap is diagnostic. If your sRPE for a 5x4-minute threshold session is 9/10 but your interval RPEs were 7, 7, 7, 8, 9 - the workout was fine, your fitness just isn't recovered enough to handle the volume. If sRPE is 6/10 but interval RPE climbed from 5 to 9 across five repeats, the workload was too much for your current fitness, even though the session felt manageable overall. Neither number tells the full story. Both together paint a complete picture.
Beginner shortcuts that wreck this: rating all sessions at 7 (avoids thinking), rating only "hard" sessions and ignoring easy ones (loses the easy-day trend), and confusing emotional fatigue ("I'm bored of this") with physical fatigue ("my legs are empty"). Rate every session. The easy ones matter as much as the hard ones for trend analysis.
Common mistakes
1. Ignoring RPE entirely in favour of data. The most data-driven athletes sometimes fall into the trap of trusting their power meter or heart rate monitor above all else. But when the numbers say "zone 2" while your legs are screaming "this is hard," your body is usually right. Ignoring RPE leads to training too hard on easy days and not hard enough on hard days - the exact opposite of polarised training.
2. Using RPE without calibration. Rating your effort as "7 out of 10" is only useful if you know what a 7 actually feels like. Most athletes under-rate their easy efforts (calling a 4 a 3) and over-rate their hard ones (calling an 8 a 9). Take two weeks to deliberately cross-reference your RPE with heart rate and power data at different intensities. Build your internal scale deliberately, not by guesswork.
3. Confusing session RPE with peak interval RPE. A workout with five hard 4-minute intervals might feel like a 9 at the peak of each interval, but the session as a whole might be a 7. Session RPE captures the overall difficulty of the entire workout including the rest periods. Momentary RPE captures the peak intensity of a specific effort. They answer different questions and should be tracked separately.
How Baseline handles this
Baseline prompts you to log your session RPE after each completed workout. Over time, the platform learns your personal RPE-to-power and RPE-to-heart-rate relationships. The daily AI insights card surfaces deviations - when your RPE is consistently higher than your power output suggests it should be, Baseline flags this as a potential sign of accumulated fatigue or early illness so you can adjust before it becomes a problem.
Further reading
RPE in multi-sport training: why your 7/10 isn't universal
Athletes who train across cycling, running, and swimming encounter a problem that single-sport athletes never face: the same RPE value means different things in different sports. A 7/10 effort on the bike might correspond to 85% of FTP and feel like steady threshold work. A 7/10 effort running might be 10 seconds per kilometre slower than your 5K pace and feel like a tempo run. A 7/10 effort in the pool might be a pace you can hold for 400 metres. Not only are the physiological demands different, but the sensation of effort varies by sport. RPE in swimming is dominated by the suffocation sensation of breath control and the burn in specific upper-body muscles. RPE in cycling is dominated by the burning sensation in the quads and the ventilatory stress of maintaining cadence. RPE in running is ecologically natural - humans evolved to run - and effort perception is often lower than objective metrics would suggest because the movement pattern is so ingrained.
The practical resolution: you cannot compare RPE values across sports directly. A "7" on the bike is not equivalent to a "7" in the pool. Maintain separate RPE scales for each sport, calibrated against sport-specific objective metrics (power for cycling, pace for running, pace-per-100m for swimming). Over time, this produces three distinct RPE-to-performance maps that let you trust your feel in each sport independently.
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.