Author(s): MATTA, P.M., BAURÈS, R., DUCLAY, J., ALAMIA, A., Institution: INSERM , Country: FRANCE, Abstract-ID: 1063

INTRODUCTION:
The influence of the mind on physical performance has been extensively demonstrated in the last decades (1). In line with these findings, we highlighted in a previous study how unconsciously manipulating time perception significantly slowed down the accumulation of neuromuscular fatigue (2). Here, we move forward by addressing two important yet unresolved questions: 1) What are the neural correlates of this effect, and 2) Is this effect persistent in the absence of motivational confounds (i.e., performance goals)?
METHODS:
24 subjects participated in four separate sessions in which they performed 100 isometric knee extensions against a fixed resistance (20% of their maximal torque). While the rest time between contractions was identical (5s) for each session, each contractions real (R) and perceived (P) time were independently manipulated. In each session, the contractions’ time was either short (10s) or long (12s), while the digital clock displayed in front of the participants was either Normal (N) or Biased (B). This led to 4 counterbalanced conditions: N10 (10s P, 10s R), N12 (12s P, 12s R), B10 (10s P, 12s R), B12 (12s P, 10s R).
Using electroencephalographic recordings, we measured power changes in motor (beta [13-31Hz]) and frontal (theta [4-8Hz], alpha [8-12Hz] and beta [13-31Hz]) areas over the 100 contractions. Simultaneously, the root mean square of the quadriceps electromyographic activity (EMG) was computed. For each measurement, we extracted the integral over all contractions. Finally, pre to post-exercise changes in the quadriceps Maximal Voluntary Torque (MVT) were assessed. Repeated measures ANOVAs and paired t-tests were performed using frequentist and Bayesian frameworks to evaluate both the difference and absence of difference between sessions.
RESULTS:
Pre to post-MVT decrease was larger in N12 (-24.2±2.3%) compared to N10 (-20.3±1.7%), B10 (-21.5±1.8%), and B12 (-20.1±1.5%) (p<.05). Similarly, EMG increase over the 100 contractions was greater in N12 (187.8±13.1a.u.) compared to N10 (180.1±9.8a.u.), B10 (181.0±9.7a.u.), and B12 (182.3±12.4a.u.) (p<.05). Importantly, there was no difference between N10 and B10 for both MVT and EMG (p>.05, Bayes Factor (BF)<.3). Regarding the underlying neural correlates, no difference was observed between the sessions in beta power of the motor area (p>.05, BF<.3). At the same time, frontal power in theta and beta bands exhibits a significant difference between N10 and N12 (p<.05), but no difference (p>.05, BF<.3) between B10 and N10, and N12 and B12, respectively.
CONCLUSION:
Our study shows a subjective time-dependent accumulation of physical fatigue irrespective of motivational factors. Interestingly, this effect is observed only when the clock is slowed down, suggesting that fatigue accumulation can be reduced but not accelerated. This effect is mediated by an oscillatory dynamic that follows subjective time in frontal but not motor areas.
1. Noakes, Appl Physiol Nutr Metab, 2011
2. Matta et al., Psychophysiology, 2023