Intensity, RPE and RIR
Intensity is measured three different ways and people constantly talk past each other because of it. Here is what each one means and when to use it.
Last updated: 1 July 2026
Overview
Intensity is one word doing three jobs, which is why gym conversations about it go nowhere.
It can mean the percentage of your one rep max on the bar, how close a set was to failure, or simply how unpleasant the session felt. Only the first two are useful for programming.
Quick Answer
Training intensity is measured either as a percentage of your one rep max, or as how close a set is to failure. Reps in reserve, or RIR, counts how many reps you could still have done. RPE is the same scale inverted, where RPE 8 means roughly two reps left.
Key Points
- Percentage of 1RM works well for strength lifts and badly for isolation work.
- RIR counts the reps you left in the tank.
- RPE 10 means no reps left, RPE 8 means about two left.
- Auto-regulation lets a programme survive a bad night's sleep.
- Most people underestimate how far from failure they actually are.
The three measures
| Measure | What it describes | Best used for |
|---|---|---|
| Percentage of 1RM | Load relative to your maximum | Squat, bench, deadlift, press |
| Reps in reserve | Reps left before failure | Any exercise, especially isolation |
| Session RPE | How hard the whole session felt | Tracking overall fatigue |
Percentage work is precise on lifts where you know your max and the max is stable. It falls apart on lateral raises, where nobody knows or cares what their one rep max is.
Reading the RPE scale
| RPE | Reps in reserve | What it feels like |
|---|---|---|
| 10 | 0 | Could not add another rep |
| 9 | 1 | One more, maybe |
| 8 | 2 | Two clean reps left |
| 7 | 3 | Comfortably hard |
| 6 or below | 4 plus | Warm up or technique work |
Most hypertrophy work sits between RPE 7 and 9. Most strength work sits between RPE 7 and 9 too, at heavier loads and lower reps.
Why auto-regulation helps
A percentage-based programme assumes every day is the same. They are not. Sleep, stress, food and life all move what a given weight feels like.
If your programme says 100kg for 5 and today 100kg moves like a maximum, grinding it out costs more than it gives. Auto-regulation means training to a target effort rather than a fixed number, so a bad day becomes a lighter session instead of a failed one.
A practical version: keep the prescribed weight but stop the set at the target RIR rather than the target rep count.
Calibrating your own judgement
Most untrained lifters are poor at estimating reps in reserve, and almost always overestimate how hard they are working. A set they call RPE 9 is often RPE 6.
The fix is to occasionally take an isolation exercise to genuine failure. Not a compound lift under a heavy bar, and not often, but enough to recalibrate what failure actually feels like.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Training everything to failure | Fatigue rises faster than stimulus | Keep most sets at 1 to 3 RIR |
| Never approaching failure | Not enough stimulus to adapt | Push the last set of each exercise |
| Using percentages on isolation work | The maths is meaningless there | Use RIR for accessories |
| Treating RPE as how tired you feel | Confuses fatigue with proximity to failure | Judge by reps left, not discomfort |
Frequently Asked Questions
Should I train to failure?
Occasionally and selectively. Failure on isolation exercises is relatively cheap. Failure on heavy compound lifts costs a lot of recovery and raises injury risk without adding much stimulus.
What RPE should most of my sets be?
Somewhere between 7 and 9 for the majority of working sets. Leaving one to three reps in reserve keeps quality high while still driving adaptation.
How do I know my RPE is accurate?
You do not, at first. It improves with experience. Taking an occasional isolation set to true failure gives you a reference point.
Is RPE better than percentages?
Neither is better in every case. Percentages suit competitive strength work with known maxes. RPE suits everything else, and handles bad days better.
Sources
National Strength and Conditioning Association - https://www.nsca.com/
American College of Sports Medicine - https://acsm.org/