Perceived Time Shapes Physical Fatigue Accumulation and Its Neural Oscillatory Correlates 2026 Matta et al

[Andy]

Recent studies suggest that fundamental physiological processes, such as physical fatigue, rely on perceived rather than actual time. However, the neural correlates underlying this effect and its disentanglement from motivational factors (i.e., performance goals) remain unknown. To investigate the time deception effect on fatigue, we developed a novel EEG design in which participants (N = 24) performed 100 isometric contractions at a fixed pace and resistance in four distinct sessions. The actual contraction duration (short or long) and the calibration of the displayed clock (normal or biased toward acceleration or deceleration) were independently manipulated across sessions to examine whether fatigue and its neural correlates evolved in response to perceived or actual time.

Our results showed a slowed-down accumulation of physical fatigue when the clock was slowed down, irrespective of motivational factors, while no symmetric effect was observed when the clock was accelerated. This time-deception effect was accompanied by frontal oscillatory dynamics that closely tracked perceived rather than actual time, while motor-related activity showed no such modulation. Further analyses highlighted the key role of frontal oscillatory dynamics in the effectiveness of the time-deception effect on physical fatigue.

Open access

 

[Jonathan Edwards]

This seems relevant to discussions previously about fatigue involving integration over accumulated signals. I don't know how good the methodology is but it sounds like a sensible experiment. The asymmetry is interesting.

 

[wallfish]

The title and abstract remind me of a replication crisis blog that critiqued a paper that claimed something along the lines of "wounds heal faster when participants are looking at a sped-up clock". I don't quite remember the source and don't seem to find it back right now.

 

[Eleanor]

So they seem to have found that muscles behave in a less fatigued way when the brain perceives less time has passed, but they don't behave in a more fatigued way when the brain perceives more time has passed. Not sure how this relates to real-world activities where people aren't constantly looking at a clock and getting beeps and flashes to tell them to start or stop moving.

And my usual question when reading conclusions which rest on data that has been crunched and averaged out in this way: is this an effect that is seen reliably in all participants? Or is there actually a lot of variation between individuals?

 

[Jonathan Edwards]

So they seem to have found that muscles behave in a less fatigued way

I am not sure they are suggesting that muscles behave differently. The perception of fatigue is less. As far as I know they are not testing for muscle fatiguability.

I suspect it translates reasonably well to real life because we have pretty good clocks built in. We can judge that something took 'too long' even if we cannot say how many clock units of time too long. We have to do that to follow music (in a shorter time frame).

It certainly fits with my experience that prolonged travel makes my clock seem to advane an hour, irrespective of time zone changes. Except that that would be an example of what they did not find (more tired when the clock sped up).

 

[Eleanor]

I am not sure they are suggesting that muscles behave differently. The perception of fatigue is less. As far as I know they are not testing for muscle fatiguability.

Sorry, what I meant is the EMG measures they were looking at ('muscles behave differently' was a very vague way of describing that!).

We first assessed the effects of real and perceived time on physical fatigue, quantified as the pre-post change in maximal voluntary torque (MVT). Analysis of the pre-post difference in MVT revealed no significant main effect of perceived time (p = 90), real time (p = 47), nor their interaction (p = 23). [...] We next examined whether perceived time modulated fatigue accumulation during the task, quantified as the EMG Root Mean Square (RMS) activity recorded across contractions—an indirect measure of physical fatigue reflecting the progressive increase in central motor drive required to maintain force output in the presence of peripheral muscle deficiency [...]

And then they looked at whether neural activity in the motor cortex correlated with it. They didn't look at subjective perception of fatigue.

They do add this:

It should be noted that EMG, while providing a good proxy of fatigue through the progressive neural drive to cope with the rising peripheral deficiency [38], remains an indirect measure that may be influenced by other factors such as alterations in motor unit action potential properties [67].

 

[Jonathan Edwards]

Sorry, what I meant is the EMG measures they were looking at ('muscles behave differently' was a very vague way of describing that!).

I had not read that bit. They seem to be measuring what Snow Leopard calls central fatigue, which determines electrophysiological patterns. So, no, not subjective fatigue directly. It seems to me like an interesting finding. It might be relevant to the mysterious 2nd day CPET measurements in ME/CFS.

 

[rvallee]

This is studying fatigue in a similar way as putting people in a sauna is studying fever. It might have some overlap but it doesn't translate seamlessly.

 

[Utsikt]

Unfortunately the conclusion is essentially marketing. They even throw in some mind-body stuff!

3.4 Conclusion​

Our study demonstrates the direct influence of time deception on physical fatigue accumulation, irrespective of maximal performance goals, and reveals key neural oscillatory correlates of this effect. We show that this influence is primarily associated with frontal oscillatory dynamics that closely track perceived time.

Building on these findings, we propose potential mechanisms underlying this mind-body interaction. By showing that psychological factors can modulate physical fatigue, our results have broad implications for performance enhancement, but also everyday life and occupational settings, suggesting ways to optimize endurance, productivity, and safety in workers and other physically demanding contexts.

Future research should further investigate the neural mechanisms driving this phenomenon from different perspectives (e.g., cardiac, respiratory or fMRI recordings) to further deepen its theoretical understanding. It may also explore applications across various contexts (e.g., sport, work, daily life) and their potential translation into clinical conditions.

 

[Utsikt]

To further explore the individual differences that may affect the strength of the deceptive effect, we considered participants’ interoceptive awareness, measured via the Multidimensional Assessment of Interoceptive Awareness (MAIA) [51] after their last session, as a potential moderating factor. We specifically focused on the ‘Noticing’ and ‘Body Listening’ subscales, which are more closely linked to bodily processes [52], as well as the ‘Attention Regulation’ subscale, given its relevance to mind-body interactions [53-55].

53 and 54 are about embodied health and 55 is about a Bayesian Brain framework for placebo and nocebo. All are opinion pieces that are presented as facts by the authors of this article.

 

[ScoutB]

Yeah this is a more plausible claim than the other mind-body time-effect study we looked at, but sounds like it's from the same line of research.

My default assumption would be that there likely are some correlations between the perception of time and fatigue, but my experience is more of fatigue or different activities changing my perception of time, not so much the other way around. (Somehow, these things only ever seem to be of interest to the mind-body folks if they go in the 'mind'->'body' direction.)

Like other studies in this area, this one seems to have collected a lot of data of different kinds and gone through it with a pretty complicated statistical analysis involving lots of decisions and trial and error of different models. The negative results didn't make it into the abstract:

We first assessed the effects of real and perceived time on physical fatigue, quantified as the pre-post change in maximal voluntary torque (MVT). Analysis of the pre-post difference in MVT revealed no significant main effect of perceived time (p = 90), real time (p = 47), nor their interaction (p = 23).

(This is the first time I've seen p-values reported without decimal places, not sure how I feel about it.)

If I'm understanding "quadriceps isometric contraction" correctly, the participants were basically holding their leg straight and tense and then releasing it (100 times). A sound indicated when they should start and stop and a visual on a screen indicated if they are straining with more or less than the 20% of maximum contraction force which they were meant to target. Both the actual time holding each contraction and the 'perceived' clock time were varied between 10 and 12 seconds, so there were 4 conditions overall, trialed on different 4 days. I'm used to studies like this randomizing the order in which the participants go through the different experimental conditions to avoid unintended biases. But I don't see any mention of that here. The task involves some skill, targeting a specific level of muscle contraction -- could there be a learning effect here?

The title and abstract remind me of a replication crisis blog that critiqued a paper that claimed something along the lines of "wounds heal faster when participants are looking at a sped-up clock". I don't quite remember the source and don't seem to find it back right now.

Maybe it was about the study linked here:

I previously came across this field via a fight between some psychologists claiming that they could make bruises heal more quickly if they showed participants a clock that ran artificially fast, and some other researchers claiming this was bad science. They wrote a nice rebuttal here:
How Statistical Challenges and Misreadings of the Literature Combine to Produce Unreplicable Science: An Example From Psychology, 2024, Gelman

It really feels like we're just doing the exact things that caused the psychology replication crisis all over again...