RPE and sRPE: The Cheapest and Most Underrated Training Load Monitoring

Subjectivity Is Not Unscientific

RPE (rating of perceived exertion) is often dismissed as an “inaccurate subjective feeling,” but extensive research shows that RPE correlates highly with objective metrics such as heart rate, lactate, and oxygen uptake—and it can capture information that objective metrics miss (mental fatigue, life stress, accumulated fatigue). When it comes to predicting training adaptation and injury risk, it often performs as well as or better than expensive wearable devices. It is the highest value-for-money monitoring tool.

Two Scales

• Borg 6–20 scale: The original version; values roughly correspond to heart rate (×10), but it is not necessarily linear for non-athletes or across different intensities.
• CR-10 / 0–10 scale: 0 = no exertion at all, 10 = maximal effort. More intuitive and suitable for sRPE calculations; this is now the more commonly used version.

sRPE: Quantifying an Entire Session into a Single Number

The key application is session RPE (sRPE): approximately 30 minutes after the session ends, rate the overall exertion of the entire session on the 0–10 scale, then multiply by the session duration in minutes to obtain the training load for that session (arbitrary units, AU).

Training load = sRPE (0–10) × duration (minutes)

Example: 90 minutes, sRPE 6 → 540 AU. Summing daily loads gives weekly load, monotony, and strain. Similar to TSS, but requires no power meter, no threshold calibration, and works across all exercise modalities—it is one of the rare tools that allows multi-sport athletes to “compare across disciplines.”

Details for Correct Use

• Timing: Ask approximately 30 minutes after the session. Too early and the rating is dominated by the final segment’s intensity; too late and memory distorts.
• Independent rating: Avoid reporting scores in front of others (social comparison distorts results), especially in team environments.
• Consistent phrasing and scale: Use fixed wording (“how hard was the entire session overall”) and the same scale to avoid drift.
• Individualized baseline: RPE varies by individual and context. Focus on personal trends and monotony rather than comparing absolute values across people.
• Complement, not replace: Cross-validate with HRV, resting heart rate, sleep, and performance tests (see related articles on HRV and PMC).

Why It Catches What Wearables Miss

sRPE integrates physiological (heart rate, metabolism) and psychobiological (mental fatigue, motivation, life stress, sleep) perceptions—precisely what purely physiological sensors cannot detect. When “the same training plan yields increasingly higher RPE,” it is often an early warning sign of excessive fatigue or impending illness, appearing earlier than objective metrics.

The Practical Meaning of Monotony

Doing similar loads every day (high monotony), even without extreme total volume, is associated with increased overtraining and injury risk. Deliberately creating hard/easy day contrast (high-low variation) lowers monotony—this is the reflection of polarization/periodization in monitoring data.

The cheapest monitoring tool is often the most looked down upon. A pen, a 0–10 number, thirty minutes after the session—it catches the “the brain is tired too” that your watch cannot measure. Don’t let expensive sensors make you forget: asking yourself how hard it felt is, in itself, science.

Related Reading

• Subjective Fatigue Assessment After Running: Applications of the RPE Scale and POMS Questionnaire
• RPE: Why “Feel” Is the Most Underrated Training Instrument
• RPE Feel-Based Pacing: Accuracy of Subjective Fatigue Perception in Long-Distance Running
• RPE in Running: How to Use Subjective Effort to Correct Pacing