PhD Defense – Pierre-Marie MATTA – Lundi 30 novembre 2026 à 14h

How beliefs shape physical effort: a multimodal neurophysiological investigation

Physical performance has traditionally been considered to be constrained by physiological factors. However, a growing body of evidence shows that psychological processes can substantially influence physical effort and performance. Yet the neurophysiological mechanisms through which these psychological factors affect the body remain poorly understood. A prominent approach to investigating this mind-body relationship consists in deceptively manipulating individuals’ beliefs while recording behavioural and physiological responses. In this thesis, we employed an original time-deception paradigm, in which perceived and actual exercise duration were experimentally dissociated, to investigate how beliefs about an ongoing effort influence physical performance and the development of fatigue.

Before investigating how beliefs might modulate physical fatigue, we first characterised its neurophysiological dynamics independently of psychological manipulation. Across Studies 1 and 2, maintaining a constant force output was associated with convergent EEG and fMRI modulations, including stronger beta desynchronisation and increasing BOLD activity in sensorimotor regions, alongside adaptations across frontal, cingulate and insular regions. These studies provided a neurophysiological reference for interpreting subsequent belief-driven modulations.

Building on this characterisation, we then investigated whether and how beliefs about elapsed time could modify this system. Study 3 showed that slowing the clock during a sustained contraction increased time to task failure, with this improvement in endurance accompanied by a slower development of neuromuscular fatigue. This raised questions about whether time deception directly alters fatigue accumulation independently of maximal performance goals, which neural mechanisms underlie this effect, and whether accelerating perceived time produces the opposite effect. We therefore used a fixed-work protocol, in which participants performed the same number and duration of contractions while perceived duration was manipulated. Study 4 showed that perceiving contractions as shorter slowed neuromuscular fatigue despite identical physical work, whereas perceiving them as longer did not accelerate it. EEG further showed that frontal theta and beta oscillatory dynamics tracked perceived rather than actual contraction duration, identifying neural signatures associated with this belief-driven modulation of fatigue. Finally, we used multimodal neurophysiological measurements to further characterise the mechanisms underlying these effects. In Study 5, EEG and fMRI showed that perceiving contractions as shorter was associated with reduced frontal activity but greater motor cortical recruitment, despite identical physical demands and lower neuromuscular fatigue. Autonomic and muscular measures revealed further physiological effects of the manipulation. Moreover, individual differences in the extent to which participants internalised the temporal manipulation partly predicted its neural and physiological effects.

Together, these studies demonstrate that beliefs about time can shape physical performance by altering not only how much fatigue individuals are willing to tolerate before disengaging, but also the rate at which fatigue accumulates. Frontal activity emerged as a consistent neural correlate of these effects, pointing to the prefrontal cortex as a candidate neural substrate linking beliefs about ongoing effort to changes in physiological regulation. These findings extend existing models of effort regulation by identifying fatigue accumulation and effort termination as two complementary routes through which psychological factors may influence the neurophysiological activity underlying physical performance. By doing so, they provide new insights into the neural and physiological mechanisms through which beliefs can shape bodily states.

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