REF-1484 · Hackett et al., 2017 · Journal of Strength and Conditioning Research · Paper · PubMed

Can I judge reps left in a set?

Near failure, roughly: error about 1 rep with up to 5 left, over 2 with 7-10 left; on leg press ≤1 only up to 3 left, in 81 adults on chest and leg press only. Not tested on a squat or a station.

Main caveat: Abstract only. Direction of error, spread, and how sets were organised aren't available.
limited evidenceMeasured on non-athletes to trained athletes

Hackett and colleagues tested whether people can estimate how many more reps they could do. Eighty-one adults (53 men, 28 women) with a broad range of resistance-training experience did up to 10 sets of 10 reps, at 70% 1RM on chest press and 80% 1RM on leg press.

After each set they reported their estimated repetitions to failure (ERF), then continued to failure to find the actual number (ARF). Error depended strongly on how far from failure the set really ended (p < 0.001): about 1 rep at ARF 0-5, more than 2 reps at ARF 7-10. Chest press was the more accurate: error ≤1 rep for ARF 0-5, against ARF 0-3 on leg press (p = 0.012).

Men were more accurate than women at specific ARFs on leg press (p = 0.008), with no such interaction on chest press. Experience made no difference. The authors conclude trainers can accurately estimate reps to failure when close to failure, and that estimates can be used to prescribe and monitor training.

Our reading: this backs the base's "2+ reps to spare" (SYNTH-44, practice) as a judgement people can make to roughly a rep on such exercises. The claim stops at these two exercises. An easy set far from failure is the set least well judged, and the abstract reports the size of the error rather than its direction.

Protocol

Design: cross-sectional; each subject estimated reps left after each set, then went on to failure as the reference.
Who: n = 81 adults (men n = 53, women n = 28); broad range of resistance-training experience. Age is not in the abstract.
Task: up to 10 sets of 10 reps at 70% 1RM (chest press) and 80% 1RM (leg press). ERF reported at the end of each set, then reps continued to failure (ARF).
Measure: accuracy as the amount of error of ERF across ARF 0-10. Rests, cues and equipment details are not in the abstract.
Funding and interests: not stated in the abstract record.

Key Results

Actual reps left (ARF)Size of error in the estimate
0-5about 1 rep
7-10more than 2 reps
Chest press≤1 rep for ARF 0-5
Leg press≤1 rep for ARF 0-3
Differences: error among ARF p < 0.001; chest press vs leg press p = 0.012; men vs women on leg press p = 0.008 at specific ARFs, no interaction on chest press.
Experience: resistance-training experience did not affect accuracy.
Not in the abstract: whether people over- or underestimated, the spread between individuals, ARF 6, and the size of the sex difference.

Mechanisms

Measured: estimate against reps actually done.
Authors' interpretation: estimates can be used to prescribe and monitor training.
Inference: every estimate was followed by a real test of it, so people may have learnt from feedback set by set; a lifter in a normal session never finds out. Accuracy in a real session could therefore be lower. Not tested in the abstract. Also, the sets at 70-80% allowed plenty of reps; low-rep heavy sets weren't examined.

Practical Application

Can I judge reps left in a set? Near failure, roughly: error about 1 rep with up to 5 left, over 2 with 7-10 left; on leg press ≤1 only up to 3 left, in 81 adults on chest and leg press only. Not tested on a squat or a station.
What it allows: SYNTH-44's practice rule, "when all sets are done with 2+ reps to spare, add load", sits inside the range people judged to about a rep on these two exercises. The rule itself isn't tested.
What it warns: a report of "many reps left" is the least reliable. Do not read 8 reps left as accurate.
Beginners and veterans: the abstract reports no effect of experience and gives no size or interval, so it gives no support for assuming a new lifter judges worse, and does not show the two judge alike. Do not extend past these lifts.

Limitations

Abstract only. Direction of error, spread, and how sets were organised aren't available. Up to 10 sets each followed by failure is a tiring protocol, and its rests are unknown.
Two exercises, two loads. Chest and leg press. Accuracy already differed between them, which is the point against generalising to a squat, a free-weight hinge or a station.
Fixed sets of 10. A heavy set of 4-6 isn't tested.
Feedback every set. May inflate accuracy against normal training (inference).
Not endurance athletes.
The authors' "accurately" is a judgement; an error of about 1 rep is 1 rep, and matters when the rule's margin is only 2.
How this entry was checked and changed
Why this level

rubric's cross-sectional or correlational study; n = 81, under the ≥100 bar for B+; a direct measurement with a true reference (reps actually done), but only two exercises and two loads, and only the abstract read