How Close to Failure Should You Train for Muscle Growth?

The question every hard set poses

You are four reps into a set of eight. You could stop at eight, or push to ten and find the rep that does not go up. How close to failure should you train, if what you want is muscle growth rather than a story about the set?

This is not a question about toughness. It is a question about price: every rep past comfortable adds fatigue the sets after it have to pay for. If the last two reps buy nothing, they are not free.

A systematic review with meta-analysis in Sports Medicine pooled the training studies that have tested this. The last rep to true failure appears to add nothing. Stopping well short of it costs you plainly.

What proximity to failure means and what got compared
How close to failure should you train for muscle growth
Stopping too early costs about half the growth
How close to failure should you train if you already lift
When going to failure is worth it
Where this sits in the wider evidence
The limits of this evidence
Common Questions About Training to Failure
How Pick It Up Helps
Further Reading & References

What proximity to failure means and what got compared

Proximity to failure is how many reps you had left when you racked the bar — usually called RIR, or reps in reserve. Stop with two good reps left and you trained at 2 RIR.

What you are counting down to needs a definition, and this is where the research gets slippery. Momentary muscular failure is the strict version — the rep you cannot complete through a full range of motion without your form breaking down — and the only definition that does not depend on someone’s judgement.

Refalo and colleagues pooled 15 training studies that measured muscle growth, and their central move was to stop treating those studies as if they asked the same question. Studies using the strict definition were separated from those using a looser one — a prescribed rep count, a self-judged stopping point — and both from studies comparing velocity-loss thresholds, where the set ends once bar speed drops by a set percentage from the fastest rep.

Velocity loss is a machine-measured stand-in for proximity to failure: reps slow as you fatigue, so a set ending at 20% velocity loss ends when the reps have slowed by about a fifth, and one ending at 40% goes deeper. That group carries most of the useful information here, because all six of those studies used trained lifters.

The studies ran 6 to 14 weeks, training two to three times a week, with groups of 10 to 89 participants.

How close to failure should you train for muscle growth

The conceptual relationship the authors propose between proximity to failure and muscle growth. Each dot is how much muscle one training condition added, not a head-to-head comparison. From Figure 5 of Refalo et al. (2023), used under CC BY 4.0.

The vertical axis is effect size — how researchers express a change so studies measuring different muscles with different machines can be pooled. It does not convert to inches on your arm; the shape is the point.

It climbs steeply on the left, then stops climbing. The condition that stopped earliest sits at 0.20. The four at the deep end — moderate velocity loss, high velocity loss, set failure and momentary failure — all land between 0.39 and 0.46, roughly double the first, and within that band going deeper stops buying anything. The final step to true failure, the dot on the far right at 0.41, is lower than the two conditions short of it.

The authors are explicit about one caution: the dots are not a direct comparison. Each is drawn from different studies with different participants, so the curve is their proposal about the underlying relationship, not a measured contest.

The direct comparisons agree with it. The cleanest isolates true failure: one group trained to momentary muscular failure, another stopped short, everything else matched. Across those there was no detectable difference in muscle growth, with an uncertainty range running from meaningfully worse to meaningfully better — the statistical way of saying the data cannot tell them apart. The velocity-loss studies land in the same place: ending sets at a greater than 25% speed drop produced no more muscle than ending them at 20 to 25%.

One result points the other way: pooling every study regardless of how it defined failure, training to failure came out ahead by a trivial margin that just cleared significance. It did not survive the authors’ own test of the statistical assumption behind it, and they treat it as noise.

One moderator matters later. Load did not formally change the answer, but the gap favouring failure was nearly twice as large in studies using light loads (0.28) as heavy ones (0.15) — not statistically reliable, and the authors treat it as weak support for the idea that stopping short matters more when the weight is light.

Stopping too early costs about half the growth

Conditions that ended sets at less than a 20% velocity drop — stopping while the reps still looked fast — produced about half the muscle growth of conditions that trained close to failure. That was the weakest result in the dataset, and the only estimate on the chart whose uncertainty range includes no growth at all.

So this is not a paper arguing that effort is overrated. Effort has a ceiling and a floor, and most of the argument in gyms is about a region above the ceiling where nothing changes. You have to get close. You do not have to arrive.

The mechanism the authors propose for the downturn is fatigue accounting. Nearing failure recruits muscle fibres harder and exposes them to more tension, which is the growth signal — but that fatigue carries into the next set and the next session. Past some point the extra tension in this set is paid for out of the tension in the following ones, and the ledger stops improving.

How close to failure should you train if you already lift

This paper cannot give you the number, and the authors say so: the proximity to failure that would maximise growth is unclear, because the groups told to stop short never had their stopping point verified. In one included study, lifters squatting to a 40% velocity loss hit failure about 56% of the time. What it bounds is the range.

Take most sets to two or three reps in reserve. Close enough that the reps are clearly slowing, short of the one that fails. This evidence does not show 2 to 3 RIR beats 1 to 2 or 3 to 4 — it shows the window is wide and both edges of it are expensive.
The error this data punishes is stopping too early, not going too deep. Once the reps have visibly slowed, going deeper is optional.
Stop chasing the last rep on heavy compounds. Whatever growth it buys is small enough that this literature struggles to detect it, and the fatigue comes out of the sets behind it.
Count your hard sets, not your failures. The authors pair a sufficient proximity to failure with roughly 12 to 20 sets per muscle group per week — the better-established variable, and the subject of our review of how many sets per week for hypertrophy.
Do not use soreness to judge whether a set was hard enough. The evidence on muscle soreness is that it tracks novelty more than effort.

When going to failure is worth it

The authors argue against treating this as a binary. Failure costs fatigue, so spend it where the fatigue is cheap:

On simpler, lower-fatigue exercises. A leg extension to failure costs far less than a squat to failure.
On the last set of an exercise or a muscle group, where there is nothing left for the fatigue to damage.
When that muscle group gets few sets — under five in a session, or trained only once or twice a week.
When you are trained rather than new to lifting. Experienced lifters handle and recover from it better.
When the load is light. People systematically underestimate how close to failure they are on lighter sets, so a light set nominally stopped short is often stopped very short.

That last point inverts on heavy work: on a heavy set you can feel where failure is, and on a set of twenty you cannot.

Where this sits in the wider evidence

This study agrees with the consensus on its main question. Grgić and colleagues in 2022 found that training to failure is not required for gains in either strength or muscle size, and does not harm them either. Refalo’s contribution is showing that holds once you stop mixing incompatible definitions of failure.

One nuance in that earlier analysis cuts against the tidy version, and it lands on experienced lifters specifically. Looking only at studies of people who already lifted, Grgić’s team did find a small but statistically significant advantage for training to failure. Refalo’s analysis cannot check it: only two of its nine failure-versus-non-failure studies used trained lifters. Hold “failure is not required” as well supported in general, and less settled for experienced lifters.

It also refines Hickmott and colleagues, who had reported that velocity losses above 25% beat those at or below it — a result driven mostly by comparisons against thresholds under 20%. Separate 20 to 25% out as its own band and the advantage for going deeper disappears.

The limits of this evidence

Most of the failure-versus-non-failure evidence is on untrained people. Seven of the nine studies in that comparison used participants who did not already lift. Hold that result more loosely than the velocity-loss result, where all six studies used trained lifters.

Fifteen studies is a thin base. The authors say their subgroup analyses are probably underpowered and a larger literature could answer differently.

Nobody knew how close the non-failure groups really got. This is the limitation the authors return to most often, and until studies verify the proximity to failure each group reached, the shape of that curve is inference.

The methods reporting was uneven. No study concealed group assignment or monitored what participants did outside it, and only one said whether it analysed everyone it enrolled.

This is about muscle size, not strength, and the two have reason to behave differently here — our plateau guide covers where they diverge.

Advanced set structures were excluded on purpose. Rest-pause and cluster sets were screened out, so none of this speaks to them.

Two of the five authors earn income as writers and practitioners in the fitness industry, which the paper discloses, and no funding supported the review. Neither points toward the null result they found.

Common Questions About Training to Failure

Is it bad to train to failure? Nothing here says failure damages your results — only that it does not improve them, while costing fatigue your later sets need. On a low-fatigue exercise or your last set, that cost is small.

How Pick It Up Helps

“Close to failure, not at it” is the right instruction and a hard one to follow, because judging how many reps you have left is a skill that degrades exactly when you need it — deep in a session, on a set that already hurts.

Pick It Up gives every set a target weight, a target rep count, and a target difficulty on a simplified RPE and RIR scale, so the intended proximity to failure is written down before you start rather than negotiated mid-set. Most sets are targeted at “medium”, which is our way of saying two to three reps in reserve — and this research is a good part of why. That sits on the near-failure side of the floor where stopping early cost people half their growth, and short of the failure end where the extra rep bought nothing measurable. We will not claim it is provably best: the evidence supports a window, not a point.

The app then updates the next set’s targets from what you reported, so a set that came in harder than planned changes what the following set asks for — the fatigue accounting this paper says matters, done for you.

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