Does Mental Fatigue Affect Your Lifting Performance?

Quick answer: Yes, a little. A meta-analysis by Solon-Júnior and colleagues, published 21 May 2026 in the European Journal of Sport Science, pooled 11 studies and found that a demanding mental task before training cut resistance exercise volume by a small-to-moderate amount (Hedges' g = -0.39). Compound lifts suffered most. The authors rate the evidence low quality.

You had a bad day at work. Six hours of spreadsheets, a meeting that should have been an email, then an hour of scrolling on the train home.

You get to the gym, load the same bar you handled fine last week, and it moves like it gained ten kilos. You get eight reps instead of ten. Nothing about your body changed since Monday.

What the researchers actually did

This is not a new experiment. It is a pooling of experiments, which is a different and in some ways stronger thing.

The team searched for randomised trials that did three specific things:

1. Make one group mentally tired with a genuinely demanding cognitive task, usually the Stroop test (naming the colour a word is printed in when the word itself spells a different colour) or 30 minutes of scrolling social media.
2. Give the control group something easy, like watching a documentary or just sitting.
3. Finish with a resistance training test measuring volume, meaning reps completed, or reps times sets times load.

Of 6,396 records screened, 11 studies survived, giving 14 separate comparisons and more than 205 participants. The exercises tested included back squats, bench press, leg press, biceps curls, push-ups and pull-ups.

The pooled result is reported as Hedges' g, a standardised effect size. Roughly speaking, 0.2 is small, 0.5 is moderate and 0.8 is large. A negative number means the mentally fatigued condition did worse.

What did they find?

The headline number is a small negative effect. Being mentally tired before you train costs you volume, but it does not wreck you.

Mental fatigue costs you reps, and compound lifts pay the most

-0.6-0.4-0.20

-0.39

-0.45

-0.2

All exercises

Multi-joint lifts

Single-joint lifts

View the data

Group	All exercises	Multi-joint lifts	Single-joint lifts
Effect on training volume (Hedges' g)	-0.39	-0.45	-0.2

That split is the most useful thing in the paper. A tired brain does not seem to interfere much with a lateral raise. It interferes with a squat.

The load you are using matters too, and not in the direction most people would guess.

Moderate loads suffer more than heavy or light ones

-0.6-0.4-0.20

-0.25

-0.4

-0.56

Bodyweight

Below 60% of 1RM

60% to 79% of 1RM

View the data

Group	Bodyweight	Below 60% of 1RM	60% to 79% of 1RM
Effect on training volume (Hedges' g)	-0.25	-0.4	-0.56

One of the included trials shows what that looks like in reps rather than effect sizes. De Lima-Junior and colleagues tested half back squats at three loads after a 30 minute Stroop task, and the review reports their drop-offs directly.

Reps lost after 30 minutes of a demanding mental task

0%5%10%15%

10.7%

13.4%

6.6%

50% of 1RM

70% of 1RM

90% of 1RM

View the data

Group	50% of 1RM	70% of 1RM	90% of 1RM
Reduction in repetitions	10.7%	13.4%	6.6%

Sessions with more total work also suffered more. Where relative volume was high, the effect was g = -0.54. Where it was moderate, g = -0.37. The longer and harder the session, the more room there is for a tired brain to cost you something.

Why does a tired brain cost you reps?

Nothing about your muscles changed while you were staring at a spreadsheet. Your legs are exactly as strong at 6pm as they were at 6am, so the link between mental fatigue and workout performance has to run through something other than the muscle itself.

What changes is how hard the work feels. In every one of these studies except one, the mentally fatigued participants rated the same effort as more effortful. That is the whole mechanism the researchers propose: mental fatigue inflates perceived exertion, and perceived exertion is what makes you rack the bar.

That explains the load pattern too. A set at 90% of 1RM is over in seconds and you know it is going to be horrible, so you tolerate the horror and finish. A set at 70% of 1RM to near failure is fifteen reps of gradually deciding whether to keep going. That decision is the thing mental fatigue interferes with. The researchers point to exactly this: sustained effort regulation across many reps is more vulnerable than one brief maximal push.

It also explains why curls survive. Fewer decisions, less coordination, lower stakes if a rep goes badly.

Worth flagging clearly: this is the authors' explanation for the pattern, not something the meta-analysis measured directly. Nobody scanned anyone's brain here.

What this study doesn't prove

The evidence is officially low quality, and the authors say so themselves. They ran a formal GRADE assessment and downgraded it twice: once because the studies induced mental fatigue in wildly different ways, and once because 205 participants is well below the 400 that GRADE wants for an outcome like this. Their own words are that the true effect may be substantially different from the estimate.

The prediction interval crosses zero. The confidence interval for the pooled effect runs from -0.55 to -0.23, which excludes zero. But the prediction interval, which estimates where a new well-powered study would land, runs from -0.86 to 0.08. In plain terms: on average mental fatigue hurts, but a future study finding no effect at all would not be shocking.

Single-joint exercises came out at p = 0.09, which means "we could not tell". It does not mean curls are immune. With this few studies, a real small effect could easily hide there.

A Stroop test is not your job. These trials used 5 to 52 minutes of a lab task performed immediately before lifting. Your actual Tuesday is eight hours of varied mental load, food, caffeine, and a commute in between. Whether the lab effect survives contact with real life is untested.

Nobody measured muscle growth. Every one of these studies looked at a single session. The authors call the long-term question, whether repeatedly training while mentally fatigued blunts hypertrophy, a critical knowledge gap. So a bad session is a bad session, not a lost month.

On the good side, the funding looks clean. All 11 included studies reported no conflicts of interest, and the review authors declare none. Support came from Brazilian and Italian public research councils, not a supplement company.

How to test this in your own training

The study reports a group average. What you actually want to know is whether your own numbers wobble on high-stress days, and there is only one way to find that out.

1. Add one word to every log entry. Before your first set, note your mental state as a single tag: fresh, ok, or fried. It takes two seconds and it is the only new data you need.
2. Do it for six to eight weeks. You need enough fried days to compare against enough fresh ones. Fewer than five or six of each and you are reading noise.
3. Compare one exercise, not the whole session. Pick a multi-joint lift you do every week in the 60% to 79% range, since that is where the review found the biggest effect. Squat, bench, row, whatever you repeat most reliably.
4. Look at reps at a fixed weight. Same load, same rep target, count what you actually got. If your fried days average a rep or two under your fresh days on the same weight, you have found your version of g = -0.39. If you can only remember the weight, run your best set through the one rep max calculator so you are comparing like for like.
5. Then change one thing. If the gap is real, try moving your hardest lift earlier in the session on bad days, or swapping a heavy triple in for a set of twelve, and see whether the gap closes.

What this changes about what you log

Doing this without a spreadsheet

You do not need to change how you log. Adding one word to a line of notes is not a system, it is a word.

The problem is what happens next. Six weeks later you have 24 workouts sitting in Apple Notes, and answering "do my fried days actually average fewer reps on bench?" means scrolling back through all of them and doing arithmetic in your head. Most people never do it, which is why most people never find out.

This is where Gym Note Plus helps. Keep typing your sessions in plain text exactly as you do now, and it parses them into per-exercise history automatically:

• Per-exercise trends so you can see whether bench reps at the same weight are drifting, without scrolling.
• Plain text in, structure out. No dropdown menus, no picking exercises from a list mid-set.
• Your whole history stays searchable, so a six-week comparison is a glance instead of an afternoon.

If you want to see what that looks like before installing anything, paste your last session into the free notes to workout translator and watch it turn into charts.

A bad session on a mentally exhausting day is not evidence you are getting weaker. It is evidence you should be logging what kind of day it was.

Frequently Asked Questions

What did the 2026 study on mental fatigue and resistance exercise find?

The Solon-Júnior meta-analysis, published 21 May 2026 in the European Journal of Sport Science, pooled 11 randomised trials and more than 205 people. Mental fatigue before lifting reduced training volume by a small-to-moderate amount, Hedges' g = -0.39. The authors graded the evidence as low quality and urged caution.

Does mental fatigue make you physically weaker?

No. Mental fatigue does not reduce the force your muscles can produce. It raises how hard a given effort feels, which makes you stop sooner. That is why the Solon-Júnior review found losses in total volume and reps completed, rather than losses in one-rep maximum strength.

Should you skip the gym after a mentally exhausting day?

The research does not support skipping. The average cost was a small drop in volume within a single session, and no study measured whether that affects muscle growth over months. A slightly worse session logged is worth more than a missed one, especially since the effect is largest on high-volume days.

Does scrolling your phone before a set hurt your lifting?

Possibly. Two of the studies in the Solon-Júnior review used 30 minutes of social media on a smartphone as the mental fatigue task, and it worked: participants rated their mental exertion higher afterwards. Whether the two minutes you spend between sets matters was not tested here.

Which exercises are most affected by mental fatigue?

Multi-joint lifts. In the Solon-Júnior meta-analysis, compound exercises like squats and bench press showed a reliable drop in volume (g = -0.45), while single-joint exercises like biceps curls did not reach statistical significance (g = -0.20, p = 0.09). Loads between 60% and 79% of 1RM were hit hardest.

Final Takeaways

• The effect is real but small. Hedges' g = -0.39 across 11 studies, which is roughly one or two reps on a set, not a collapse.
• Compound lifts at moderate loads are the sore spot. That is where the review found g = -0.45 and g = -0.56, and where you should look for it in your own numbers.
• The mechanism is perception, not muscle. Mental fatigue makes the same weight feel heavier, so you quit earlier. It does not make you weaker. If you already track effort, our guide to RPE vs RIR covers how to record that honestly.
• One bad session proves nothing. Before you conclude anything, read why you might be getting weaker in the gym, because most causes are more mundane than this one.
• Log your head as well as your lifts. One word per session for six weeks is enough to find out whether this applies to you, and no study can answer that question for you.