Research · 3 min read · 2026-10-12
Why we ask how hard the run felt
Rating the whole session from 0 to 10 and multiplying by the minutes is a simple, well-tested way to measure training load, also for intervals.
After each run PX7 Training asks you a simple question: how hard did the whole session feel? It may seem old-fashioned when your watch records heart rate every second. Here is the research behind the question.
What the researchers did
In 2001, Carl Foster and colleagues tested a simple way to measure training load. After a session, you rate how hard the whole session was on a scale from 0 to 10, and multiply that rating by the number of minutes. They called it session RPE.
They compared it with a method based on heart rate, both in steady and interval cycling and in basketball practice.
What they found
The two methods followed each other consistently, both on the bike and on the court. Session RPE gave higher numbers than the heart rate method, but the relationship between them was stable. The researchers concluded that session RPE works across very different kinds of exercise, including hard intervals, where heart rate alone is harder to interpret.
What it means for you
How a session felt is real information. Heart rate lags behind in short intervals and is affected by heat, caffeine and sleep. Your own rating of the whole session captures what the watch can't, such as heavy legs or a stressful day.
Rate the whole session, not the hardest moment, and try to do it the same way each time, for example a little while after you have finished.
What the study can't tell you
Session RPE describes how demanding a session was. It doesn't measure your fitness, and one high rating doesn't mean you are overtrained. A session can also feel hard because you are tired, not because it was a big workout.
How we use it
PX7 Training keeps your rating alongside what you actually ran. A hard rating doesn't count as extra training. If several comparable sessions feel clearly harder than expected, and you also report that you are tired, the next sessions become easier.
Source
- Foster et al. (2001), A new approach to monitoring exercise training. Journal of Strength and Conditioning Research.
Written by Jørgen Larsen for PX7 Training.