Reps in reserve: how hard each set should feel

If you’ve done a WITHIN workout, you’ve heard me say “stop with one to three reps left.” That’s reps in reserve, or RIR: how many more good reps you could have done when you ended the set.

It sounds like a tiny detail. It’s not. It’s the difference between training that builds you up and training that just wears you out.

Okay, but why not just go until I can’t?

I get it. Going to failure feels like you did something. But that last grindy rep is usually where your form falls apart, fatigue piles up, and your next set gets worse.

And for building muscle, it doesn’t seem to buy you much. A 2023 meta-analysis of 15 studies compared training to failure with stopping a little short. Any extra muscle growth from going to failure was trivial at best, and when failure was defined strictly (as in, you literally could not do one more rep), there was no advantage at all. [1]

Now, before anyone takes that and runs: this does not mean easy sets work. Effort still matters. You need to be close to your limit. You just don’t need to live on the edge of it every single set.

How to tell where you are

At the end of a set, ask yourself honestly: how many more clean reps could I do right now? Not shaky, ugly, back-arching reps. Clean ones, same speed, same form.

Zero? That was failure. One to three? You’re right where you should be. Five or more? Love that for you, but the weight is too light. Go up next time.

Researchers built a rating scale around this exact question: a 10 means zero reps left, a 9 means one left, and so on. In a 2016 study, people’s ratings tracked closely with how fast the bar was moving, in both experienced lifters and beginners. [2] It’s a practical way to coach effort without a lab, and like anything, you get better at it the more you do it.

How we use it in WITHIN

On the big stuff (squats, hinges, rows, presses), most sets end with one to three reps left. Smaller, more stable moves like lateral raises or curls can go a little closer.

When you hit the top of your rep range on every set and still have one to three reps in the tank, you’ve earned more weight. Write it down, go up next time, and watch the numbers climb.

Hard enough to change you. Not so hard you dread the next one. That’s the whole point.

Sources

1. Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ. Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis. Sports Medicine. 2023;53(3):649–665. doi.org/10.1007/s40279-022-01784-y
2. Zourdos MC, Klemp A, Dolan C, et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. Journal of Strength and Conditioning Research. 2016;30(1):267–275. doi.org/10.1519/JSC.0000000000001049