Mental fatigue limits strength: an experiment with 931 repetitions

A study in the European Journal of Sport Science: 22 recreational athletes performed strength training exercises over 12 sessions at home. Half of them performed cognitive tasks before and after training — the Stroop task on their phones. Post-test results: +33% repetitions in the bench press, +93% in the bicep curl, +28% in the jump squat. And all this with lower perceived effort — the work felt easier subjectively.

Where did the idea come from

In 2009, the Marcora group published an experiment: people performed a 90-minute Stroop task (reading the colours of words despite a mixed background). Then they got on an ergometer and cycled until exhaustion. They lasted less long – with the same legs and heart.

The conclusion was counterintuitive: physical endurance is limited not by muscles or VO2max, but by the brain's willingness to tolerate effort. If the brain is pre-fatigued cognitively, the muscles “give up” before their objective limit.

This is where the concept grew from Brain Endurance Training (BET) — of combined cognitive-physical training. The logic is simple: if the brain is trained to work in a state of cognitive fatigue, then in the gym, it will endure more.

Over the past 15 years, around 12 randomised trials involving BET have been conducted – involving runners, cyclists and footballers. The results were consistent: a 5–15% improvement in endurance performance and a reduction in perceived effort. However, almost all of these were conducted in a laboratory setting under supervision, and almost all focused on endurance.

Rautu et al.'s 2026 study is new in two dimensions: Remote (at home, without a supervisor) and forcefully (not for endurance).

What have [they/you] done

22 recreational athletes (training 2-4 times a week). Pre/post design:

Laboratory pre-test: bench press, preacher curl, squat jump — to muscle failure
12 home training sessions Over 6 weeks, remotely:
- Control (ET): standard strength protocol — same exercises, reps to failure
- BET Group: the same protocol + Stroop task 20 mins before training and 13 mins after
Laboratory post-test: the same three exercises to failure

The physical exertion was identical in both groups. The difference is only in the cognitive tasks around the training.

What did it show

Changes to post-test, BET vs ET

General repetitions to failure: +50%
Bench press: +33%
Preacher curl +93%
Squat jump +28%

In the control group, there was a small change in all three metrics.

The most interesting result is— Rating of Perceived Exertion (RPE) after the BET group training decreased. In other words, the athletes performed more repetitions with the 30-90%, but subjectively it felt easier.

Why might this work

Working hypothesis, supported by previous BET studies with NIRS and EEG measurements:

Anterior cingulate cortex — a part of the brain that assesses “how much more effort can I put in”. During physical exertion, the ACC compares the “cost” of effort (perceived effort) with the “value” of the goal. When the cost exceeds the value, movement is “switched off”. This is not a conscious decision, but a regulatory mechanism.

When cognitive tasks are added to training, the brain gets used to operating with a higher cognitive load. The ACC adapts to sustain effort for longer. When the athlete returns to purely physical tasks after 6 weeks, the “cost > benefit” threshold shifts. More can be achieved for the same subjective effort.

Analogy: I trained with a backpack of weights. Without the backpack, everything is easier.

Caveats: what we don't know

n=22 — that's not many. This is not a meta-analysis. Individual preliminary BET studies involved between 30 and 90 participants. The effect sizes in Rautu (+93%) are large and require replication, particularly in other laboratories.

Recreational athletes, not elite. A review of BET in elite sport (Tofari et al. 2026, Scandinavian Journal of Medicine & Science in Sports) showed that the effects are smaller at elite level—professionals are already accustomed to the high cognitive load on the pitch. At recreational level, there is greater scope for improvement. It’s not a case of “+93% in every gym”.

Short-term effect. 6 weeks is the start of adaptation. Whether the effect is maintained for 3-6 months without BET is unknown.

Sequential, not concurrent. The Stroop test was performed before and after training, not during. The review by André et al. 2025 in Frontiers in Psychology notes: a dual-task (simultaneously) theoretically provides a stronger effect than a sequential one. This means it is possible that a different format works even better – but this is currently a hypothesis.

One type of cognitive task. Stroop was taken – incongruent version. Will there be an effect with n-back, AX-CPT, chess, Sudoku – not directly studied in this research.

Which of these is useful?

If you train regularly and hit a ceiling on reps or weight:

Perhaps the problem isn't the muscles. The ceiling can be in readiness for the brain to tolerate. A simple experiment: add 15-20 minutes of cognitive tasks (the Stroop app on your phone, it's free) to your training for 4-6 weeks and see the repetitions until failure.
Perceptual effort is an informative metric. If an exercise subjectively “becomes easier” with the same objective indicators - something fundamental has changed.
Don't expect +93% over 12 home sessions — this is a laboratory maximum in recreational athletes with a specific protocol. The real “in the field” effect will be smaller.
This is a new paradigm, not a magic bullet. BET complements, it doesn't replace, physical training. Without 12 strength sessions, Stroop on its own does not provide strength.

Main source Rautu A, Woods J, Mortimer H, et al. (2026). Remote-Based Brain Endurance Training Enhances Bench Press, Preacher Curl, and Jump Squat Performance in Recreational Athletes. European Journal of Sport Science. DOI: 10.1002/ejsc.70173

Additionally:

Marcora SM, Staiano W, Manning V (2009). Mental fatigue impairs physical performance in humans. Journal of Applied Physiology
André N, Audiffren M, Englert C (2025). Brain endurance training as a strategy for reducing mental fatigue. Frontiers in Psychology. DOI: 10.3389/fpsyg.2025.1616171

— Vitaliy, Founder of life:)on