Perception of effort, defined as “the conscious sensation of hard, heavy and strenuous exercise”, is known to regulate endurance performance and human behaviour. Perception of effort has recently been shown to be exacerbated by mental exertion and is also known to be a main feature of fatigue. However, to date, not only its neurophysiology but also how manipulations of perceived exertion might impact endurance performance remain poorly understood. The main aim of this thesis was to investigate how manipulations of perceived exertion might impact endurance performance.
This thesis is divided in two parts: central and peripheral manipulations of perceived exertion. In each part, three experimental chapters aimed to get a better insight in the neurophysiology of perceived exertion and its impact on endurance performance.
In the first part (central manipulations), we firstly investigated the impact of exacerbating perceived exertion via mental exertion involving the response inhibition process on self-paced running endurance performance. This study demonstrated that as with time to exhaustion tests, time trial performance is impaired following mental exertion leading to mental fatigue. Secondly, we investigated whether mental exertion leading to mental fatigue could alter the rate of central fatigue development during constant load whole-body exercise. This study demonstrated that the exacerbated perception of effort in presence of mental fatigue does not reflect an altered rate of central fatigue development, but is likely to be due to i) an impaired central motor command and/or ii) an alteration of the central processing of the corollary discharge. Thirdly, we investigated whether mental exertion could impact the repeatability of maximal voluntary contraction of the knee extensors. We found that contrary to submaximal exercise, force production capacity is not altered by mental exertion. Finally, these three studies demonstrated that i) mental exertion negatively impacts submaximal exercise but not maximal exercise and that ii) mental fatigue differs from central fatigue.
In the second part (peripheral manipulation), we firstly developed and tested the reliability of a new endurance exercise model non-limited by the cardiorespiratory system (one leg dynamic exercise), which will be of benefits for future researches aiming to manipulate feedback from group III-IV muscle afferents. Secondly, we described neuromuscular alterations induced by this exercise and tested a new methodology to indirectly measure feedback from group III-IV muscle afferents. This study demonstrated that one leg dynamic exercise induced central and peripheral fatigue and also a decrease in spinal excitability associated with an increase in cortical excitability. Furthermore, this study also suggests that monitoring cardiovascular responses during muscle occlusion might be a suitable tool to indirectly measure feedback from group III-IV muscle afferents. Thirdly, we tested the corollary discharge and afferent feedback model of perceived exertion with electromyostimulation. This study demonstrated for the first time that for the same force output, perception of effort generation is independent of muscle afferents and reflects the magnitude of the central motor command (manipulated by electromyostimulation). All together, these findings provide further evidence in support of the corollary discharge model of perceived exertion, and provide a new exercise model to investigate and manipulate perception of effort.
This thesis, when integrating both experimental parts, provides new insight on how perception of effort regulates endurance performance. Specifically, it demonstrates how muscle fatigue is a contributor of the continuous increase in perception of effort during endurance exercise, but also that other contributors play a role in this increase in perception of effort. Indeed, we demonstrated for the first time that i) perception of effort alterations in the presence of mental fatigue is independent of any alterations of the neuromuscular system, and ii) muscle afferents does not directly impact perception of effort, but may influence it indirectly via their role in motor control
