Two Ways to Measure the Same Thing
When serious lifters and coaches talk about training intensity, they've largely moved away from pure percentages. "Work at 80% of your 1RM" sounds precise, but your 1RM fluctuates based on sleep, stress, nutrition, and accumulated fatigue. A fixed percentage doesn't account for how you're actually feeling.
RPE and RIR are two systems that solve this problem. Both are ways of quantifying how hard a set was — but they approach it from opposite directions.
What Is RPE?
RPE stands for Rate of Perceived Exertion. On the standard Borg CR10 scale adapted for strength training, it runs from 1 to 10:
- RPE 10 — Maximum effort. You could not have done another rep.
- RPE 9 — Could have done one more rep.
- RPE 8 — Could have done two more reps.
- RPE 7 — Could have done three more reps.
- RPE 6 — Four or more reps left, set felt comfortable.
RPE is a *forward-looking* assessment — you rate the set based on your overall effort and how close you were to failure.
What Is RIR?
RIR stands for Reps in Reserve. It's simply the number of additional reps you could have completed before hitting failure:
- 0 RIR — Complete failure. No reps left.
- 1 RIR — Could have done one more rep.
- 2 RIR — Could have done two more reps.
- 3 RIR — Three reps left in the tank.
RIR is a *concrete count* — rather than rating effort on a scale, you estimate the specific number of reps remaining.
RPE vs RIR: How They Relate
They're essentially the same information expressed differently:
| RPE | RIR |
|-----|-----|
| RPE 10 | 0 RIR |
| RPE 9 | 1 RIR |
| RPE 8 | 2 RIR |
| RPE 7 | 3 RIR |
| RPE 6 | 4 RIR |
The difference is in how you arrive at the number. RPE asks you to rate the overall effort of the set on a scale. RIR asks you to count the reps you had left.
For most people, RIR is more intuitive initially — it's easier to think "I had 2 reps left" than to map effort onto an abstract scale. But experienced lifters often find RPE more flexible, because it captures nuances beyond just rep count — like how the set felt technically, whether form was breaking down, or whether the effort was sustainable.
Which Is More Accurate?
Neither is perfectly accurate. Research on self-reported RIR and RPE consistently shows that lifters tend to overestimate the reps they have left (i.e., report lower RPE than the set actually warranted) — especially less experienced lifters and on lower body exercises.
The practical implication: err on the side of harder. If you think you had 3 reps left, you probably had 2. If you feel like you were at RPE 7, it was probably RPE 8.
Accuracy improves with practice. The more you consciously track RPE or RIR over time, the better your calibration becomes. This is one reason logging it consistently matters.
When to Use Each
Use RIR when:
- You're newer to intensity tracking and want something concrete
- You're writing a programme for someone else who needs clear instructions ("leave 2 reps in the tank")
- The exercise is something you know well and can count precisely
Use RPE when:
- You're an experienced lifter comfortable with effort-based self-assessment
- You want to capture technical failure, not just muscular failure (a set where form broke down at RPE 9 is different from a clean set at RPE 9)
- You're using an app or system that tracks RPE per set
For practical purposes: pick one and use it consistently. The system you actually track is better than the theoretically superior system you don't.
Applying This in Your Training
A simple framework for most hypertrophy training:
- Work sets: Target RPE 7–9 (1–3 RIR). High enough effort to stimulate growth, enough buffer to maintain form.
- Top sets / heavy singles: RPE 9–10 (0–1 RIR) — maximum effort, used sparingly.
- Warm-up sets: RPE 5–6 (4+ RIR) — preparing for the work sets, not grinding.
Tracking RPE across a mesocycle helps you spot fatigue accumulation before it becomes a problem. If the same weights start feeling harder week over week, that's a signal you might need a deload — not a sign to push harder.
Tracking RPE With Soma
Soma logs RPE per set alongside your weight and reps. Over time, this builds a picture of how your effort levels trend — making it easy to see when you're consistently hitting your targets and when fatigue is accumulating.
The AI coach uses your RPE data to adjust your programming: if you're consistently below your target RPE, it increases the load; if you're above it, it may suggest pulling back. It's auto-regulation built into the app.
If you're not tracking RPE yet, it's worth starting — even just estimating it to get used to the scale. The difference it makes to how you train is significant.
Download Soma free on the App Store to start tracking RPE on every set.