Percent of one-rep max is the textbook way to set resistance training intensity, and almost nobody uses it for a home program. A percentage needs a measured, stable maximum and equipment that loads in small steps. The patient has a chair, two bands and a backpack of books, their strength changes faster than you can re-test it, and a true maximal effort is off the table for many of them. What you can ask any patient, with any equipment, is how many more reps they could have done. Here is how the scale works, where it breaks, and how a rating becomes a load decision.
Two scales, one of them built for this
The Borg CR10 runs from 0 to 10 and was built around whole-body exertion and breathlessness. It suits a walking program, less so a set of band rows, where a patient can be breathing easily while their rotator cuff has one rep left. Zourdos and colleagues published a resistance-specific alternative in the Journal of Strength and Conditioning Research in 2016. It anchors each number to reps in reserve (RIR): 10 means no more reps were possible, 9 means one more, 8 means two more, and so on. In 29 squatters, bar velocity and the rating were strongly and inversely related (r = -0.88 in experienced lifters, -0.77 in novices), so the number tracks real proximity to failure.
How accurate the estimates are
Halperin and colleagues pooled 12 studies with 414 participants in Sports Medicine in 2022. On average people underpredicted the reps they had left by about one (0.95 reps, 95 percent CI 0.17 to 1.73). Accuracy improved when the rating was given close to failure, when sets were 12 reps or fewer, and with heavier loads; training status made no difference. The practical reading: a 2 RIR estimate is usually close, a 6 RIR estimate is a guess. Zourdos also found novices rated a true maximal squat below 10, so an untrained patient's first ratings tend to sit low until they have felt a hard set.
Does it work as well as percentages
In general training populations, yes: a 2022 meta-analysis of six load autoregulation studies in Sports Medicine Open found no significant strength difference between RPE or velocity-based and percentage-based loading. Clinical evidence is thinner but points the same way. A 2024 pilot in cardiac rehabilitation randomised 16 men with coronary artery disease (mean age 60) to nine weeks of resistance training with identical sets, reps and rests, load set either by RIR-based RPE or by percent of estimated 1RM. Both groups got stronger on every exercise, with no between-group differences. A pilot, not a verdict, but the closest setting to yours.
Turning the goal into a target
- Early after injury or surgery, or when irritability is high: 5 to 6 RIR, mostly to teach the scale.
- Building capacity: 3 to 4 RIR. Enough to be a stimulus, far enough from failure that form holds.
- Strength work in later-stage rehab: 2 to 3 RIR, where estimates are most accurate and the dose resembles real strength training.
- Keep sets at 12 reps or fewer when you want a reliable rating; 20 band pulls at 3 RIR tells you less than 8 at 3 RIR.
- Write the target as a range: "3 sets of 8 at 2 to 3 RIR" works with whatever load the patient has.
Teaching a patient to rate a set
Do the first few sets in the clinic. Ask "how many more could you have done with good form?" rather than "how hard was that?", because the first question has a concrete answer. Where it is safe, let them take a set until form starts to go and compare it with what they predicted. That calibration set is worth more than any explanation. Have them rate straight after the set, and warn them most people underestimate by a rep.
Using the rating to progress
More RIR than the target on every set for two consecutive sessions: add load: the next band, a heavier backpack, a longer lever. Fewer RIR than the target: hold or drop the load. On target: leave the load and move reps or sets instead. The rating does the job a 1RM re-test would, every session, for free.
For sets, reps and rest, the other half of the prescription, see our guide to sets, reps and rest
Adjusting between visits
Effort ratings earn their place in remote monitoring. When a home session is recorded with a camera-guided platform such as KineTrue, each set carries the reps completed, the movement quality and the patient's own effort rating. A clinician scanning the week can spot three sets of 10 at 5 RIR on an exercise prescribed at 2 to 3 RIR and change the load before the next appointment, instead of discovering a fortnight of under-dosing at the visit. A rating drifting up to 10 on an unchanged load is the warning in the other direction.
Effort ratings describe fatigue, not pain. Sharp or increasing pain, swelling, or a set that feels unusually hard at a load that was fine last week calls for stopping and reviewing the exercise, not adjusting the RIR target. Patients with cardiac, respiratory or other conditions where maximal effort is restricted need a clinician-set ceiling before any RIR work starts.