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7 min readendurance / running / focus

Cyclists lost 8 watts after a mental task: how to time hard sessions

I run trainings and write code during the day, then train in the evening. In 2019, ten under-23 road cyclists rode a 30-minute time trial twice: once after 30 minutes of a Stroop task, once after a quiet activity. Mean power came in at 287 W after the Stroop task against 295 W after the control. Heart rate, blood lactate and perceived exertion matched across the two rides.

What the research shows.

Samuele Marcora, Walter Staiano and Victoria Manning ran the trial that opened this question. Sixteen participants cycled to exhaustion at 80% of peak power output after either 90 minutes of a demanding cognitive task or 90 minutes of emotionally neutral documentaries 1. Time to exhaustion fell from 754 ± 339 s to 640 ± 316 s (p = 0.003), a loss of 15%. Heart rate, oxygen uptake and blood lactate during the ride held steady, and participants stopped at the same maximal rating of perceived exertion in both conditions. They arrived at that rating sooner. The cognitive task changed the effort they felt at a given workload and left the physiology alone.

Jeroen Van Cutsem and colleagues reviewed 11 studies built on that design 2. The pattern repeated: shorter time to exhaustion, lower self-selected power or speed, longer completion times, and perceived exertion above normal throughout. Heart rate, blood lactate, oxygen uptake, cardiac output and maximal aerobic capacity were unaffected. Maximal strength, power and anaerobic work came out unchanged as well, which narrows the target. A heavy squat set does not care how your morning went. A 40-minute threshold run does.

Luca Filipas, Gabriele Gallo, Luca Pollastri and Antonio La Torre took the design to trained riders 3. Their ten under-23 cyclists lost 8 W of mean power (287 ± 23 against 295 ± 23, p = 0.007) and 2 rpm of cadence (100 ± 7 against 102 ± 6, p = 0.043). Perceived exertion showed no difference between conditions (p = 0.710), and neither did heart rate or lactate. The riders could not feel the deficit. The power meter recorded it.

Benjamin Pageaux, Romuald Lepers, Kristina Dietz and Marcora sent 12 physically active subjects into a 5 km treadmill time trial after 30 minutes of an incongruent Stroop task or a congruent control 4. Perceived exertion during the run was 13.5 ± 1.3 against 12.4 ± 1.3. Pacing strategy, heart rate and lactate did not shift, and the inhibition task produced no reported feeling of mental fatigue at all. Performance dropped without the sensation that is supposed to explain it.

Training status changes the size of the problem. Kristy Martin and co-authors compared 11 professional and 9 recreational road cyclists on a 20-minute time trial after mental exertion 5. The recreational riders fell from 226 ± 25 W to 216 ± 33 W (p = 0.014). The professionals went from 326 ± 35 W to 323 ± 42 W (p = 0.502). Those professionals also produced 705 ± 68 correct responses on the Stroop task against 576 ± 74 for the recreational group.

The effect is real and small.

Denver Brown and colleagues pooled 73 studies, 91 comparisons and 2,581 participants 6. Prior cognitive exertion cost g = -0.38 (95% CI -0.46 to -0.31) across physical outcomes, and g = -0.26 for aerobic performance. Maximal anaerobic performance was untouched (g = 0.10). Between-subject designs returned -0.65 against -0.28 for within-subject designs, the direction you would expect if part of the effect comes from the design rather than the athlete.

Darías Holgado, Cristian Mesquida and Rafael Román-Caballero then audited the literature itself 7. Their traditional meta-analysis gave dz = -0.54 (95% CI -0.68 to -0.40). A robust Bayesian meta-analysis found strong evidence of publication bias (BFpb > 1000) and inconclusive evidence for the effect: adjusted dz = 0.01 (95% CrI -0.46 to 0.37). Treating -0.54 as the true effect, the median study in that body of work had a 39% chance of detecting it. The most forgiving correction method brought the estimate to -0.36.

The best-powered test landed this year. Jelle Habay and colleagues put 117 participants through 45 minutes of an individualized Stroop task or 45 minutes of a documentary of their choice, then a 6-minute GoNoGo task and a 20-minute cycling time trial 8. Reaction time on the GoNoGo task worsened (p < 0.001). Ratings of mental fatigue, physical fatigue and perceived exertion all ran higher during the ride. Distance covered moved by d = 0.20 and missed the threshold (p = 0.059), while cadence dropped (p = 0.042, d = 0.22).

Plan for 2 to 3% off your output on a hard aerobic session, with the change in perceived effort more dependable than the change in performance, and both shrinking as your training age rises.

The protocol.

  1. Put your hardest aerobic session ahead of your hardest thinking block. 30 to 45 minutes of sustained concentration was enough to produce every effect above, and the trials that used 90 minutes did not find a bigger one.
  2. Govern that session by pace or power. Perceived exertion is the variable these tasks corrupt; heart rate, lactate and oxygen uptake stay honest. Write your target splits down before you leave the house and hold them.
  3. Keep the numbers in front of you while you work. Neil Dallaway, Sean Leo and Christopher Ring gave 63 participants a 20-minute cognitive task between two bouts of a self-paced handgrip endurance task 9. Output fell 14.4% in the group with no feedback, against 2.4% with visual performance feedback and 2.6% in the control group. A lap-pace field on your watch does that job.
  4. Run the key session with other people or against a clock. Ferreira and colleagues had 24 professional cyclists ride a 20 km time trial under four conditions 10. Mental fatigue alone gave the worst total time, power output and cadence. A head-to-head virtual opponent improved all three without restoring the control level. Being a professional was no shield in this one.
  5. Move lifting and short intervals into the post-work slot, and protect the long efforts. Maximal strength, power and anaerobic work survived mental fatigue across the 11 studies Van Cutsem reviewed.
  6. Stop quoting the 15%. That number comes from 16 untrained participants riding at a fixed workload to exhaustion. The field figures are 8 W in trained cyclists and d = 0.20 in 117 riders.
  7. Measure your own cost across a block, not in one test. Repeat a 20-minute effort every two weeks, half of them on protected mornings and half after 45 minutes of meetings, then compare the two means. An effect of d = 0.20 needs a dozen pairs before it clears your day-to-day noise.

Open next week's calendar, find the session you care about most, and look at the 90 minutes sitting in front of it. If a block of meetings is parked there, move one of the two.

Sources.

  1. Marcora, S.M., Staiano, W., Manning, V. (2009). Mental fatigue impairs physical performance in humans. Journal of Applied Physiology, 106(3), 857-864. doi:10.1152/japplphysiol.91324.2008
  2. Van Cutsem, J., Marcora, S., De Pauw, K., Bailey, S., Meeusen, R., Roelands, B. (2017). The effects of mental fatigue on physical performance: a systematic review. Sports Medicine, 47(8), 1569-1588. doi:10.1007/s40279-016-0672-0
  3. Filipas, L., Gallo, G., Pollastri, L., La Torre, A. (2019). Mental fatigue impairs time trial performance in sub-elite under 23 cyclists. PLOS ONE, 14(6), e0218405. doi:10.1371/journal.pone.0218405
  4. Pageaux, B., Lepers, R., Dietz, K.C., Marcora, S.M. (2014). Response inhibition impairs subsequent self-paced endurance performance. European Journal of Applied Physiology, 114(5), 1095-1105. doi:10.1007/s00421-014-2838-5
  5. Martin, K., Staiano, W., Menaspà, P., Hennessey, T., Marcora, S., Keegan, R., Thompson, K., Martin, D., Halson, S., Rattray, B. (2016). Superior inhibitory control and resistance to mental fatigue in professional road cyclists. PLOS ONE, 11(7), e0159907. doi:10.1371/journal.pone.0159907
  6. Brown, D.M.Y., Graham, J.D., Innes, K.I., Harris, S., Flemington, A., Bray, S.R. (2020). Effects of prior cognitive exertion on physical performance: a systematic review and meta-analysis. Sports Medicine, 50(3), 497-529. doi:10.1007/s40279-019-01204-8
  7. Holgado, D., Mesquida, C., Román-Caballero, R. (2023). Assessing the evidential value of mental fatigue and exercise research. Sports Medicine, 53, 2293-2307. doi:10.1007/s40279-023-01926-w
  8. Habay, J., et al. (2026). Mental fatigue negatively impacts cognitive and physical performance outcomes: a large-scale randomized crossover trial. Medicine & Science in Sports & Exercise, 58(2), 225-241. doi:10.1249/MSS.0000000000003852
  9. Dallaway, N., Leo, S., Ring, C. (2022). How am I doing? Performance feedback mitigates the effects of mental fatigue on endurance exercise performance. Psychology of Sport and Exercise, 62, 102210. doi:10.1016/j.psychsport.2022.102210
  10. Ferreira, M.E.C., et al. (2023). Head-to-head opponent mitigates mental fatigue effects during a 20-km time trial in well-trained cyclists. Scandinavian Journal of Medicine & Science in Sports, 33(10), 1984-1997. doi:10.1111/sms.14445

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