Mental fatigue induced by prolonged motor imagery increases perception of effort and the activity of motor areas

Abstract

Recent literature suggests that when prolonged, motor imagery (MI) induces mental fatigue and negatively impacts subsequent physical exercise. The aim of this study was to confirm this possibility with neurophysiological and self-reported measures. Thirteen participants performed 200 imagined isometric knee extension contractions (Prolonged MI condition) or watched a documentary (Control condition), and then performed 150 actual isometric knee extensions.Electroencephalography was continuously recorded to obtain motor-related cortical potential amplitude at Cz electrode (MRCP, index of motor area activity) for each imagined and actual contractions. Electromyography of the vastus lateralis muscle as well as the perceived effort required to perform prolonged MI, watch the documentary, and perform the actual contractions were measured. During prolonged MI, mental fatigue level, the effort required to imagine the contractions and MRCP amplitude increased over time. The increase in the effort required to imagine the contractions was significantly correlated with the MRCP amplitude. During the physical exercise, a significant condition × time interaction revealed a greater increase over time in perceived effort in the prolonged MI condition compared to the control condition, as well as a specific alteration in EMG RMS of the vastus lateralis muscle. These alterations observed in the presence of mental fatigue during actual contractions, combined with those observed during prolonged MI, suggest that prolonged MI may impair the motor command required to perform imagined or actual contractions. While the observed effect of mental fatigue on MRCP amplitude was clear during MI, future studies should tailor the physical exercise to minimize the exerciseinduced decrease in force production capacity and control for its confounding effects on MRCP amplitude in the presence of mental fatigue.

Perception of effort during an isometric contraction is influenced by prior muscle lengthening or shortening

“…The origin for the perception of effort can be explained by the corollary discharge model, such that the efferent copy of generated motor commands are processed to generate the perception of effort (Christensen et al, 2007; de Morree et al, 2012; Marcora, 2009; Pageaux & Gaveau, 2016; Pageaux, 2016; Zénon et al, 2015). Movement related cortical potential, an electroencephalography marker of the motor command (de Morree et al, 2012; Jaquet et al 2021) (REFs), and EMG amplitude have been shown to both increase during active muscle contractions. During muscle fatiguing tasks, both dynamic (de Morree et al, 2012) and isometric (Guo et al, 2017) muscle contractions have been shown to increase perceived effort and EMG, as well as larger movement related cortical potential amplitude, further substantiating that motor command influences perceived effort during active contraction.…”

Typical somatomotor physiology of the hand is preserved in a patient with an amputated arm

“…Part of the latency between the cue onset and the peak of the cortical response can be explained by the lag between the interpretation of the cue and movement initiation, which in the executed movements of the patient already accounted for ~0.5s. Another factor that could have contributed to this ~1s latency may be related to the fact that motor imagery can be demanding in terms of mental fatigue and effort (Papadelis et al 2007;Jacquet et al 2020). In terms of decoding, both the transient and the sustained responses contained information about finger movements.…”

Perception of effort and the allocation of physical resources: a generalization to upper-limb motor tasks

“…Indeed, the intensity of perception of effort during a motor task has been extensively shown to be responsive to changes in task difficulty imposed by various experimental manipulations. As an example, perception of effort is altered by the intensity of muscle contraction (e.g., de Morree & Marcora, 2010, the presence of muscle or mental fatigue (e.g., Jacquet et al, 2021;Pageaux & Lepers, 2016;Pageaux & Lepers, 2018) or changes in environmental conditions (e.g., Borg et al, 2018;Girard & Racinais, 2014;Jeffries et al, 2019). In our study, to test the possibility to monitor the exercise intensity during upper-limb motor tasks, we altered task difficulty by manipulating the physical demand of the tasks performed via imposing various movement tempos or adding weight on the forearm.…”

“…Perception of effort is widely investigated during global locomotor tasks, such as walking or cycling, in both healthy and symptomatic populations (Au et al, 2017;Décombe et al, 2020;Flairty & Scheadler, 2020;Horstman et al, 1979;Zinoubi et al, 2018) to prescribe and monitor exercise (Azevedo et al, 2016;Eston & Parfitt, 2018;Impellizzeri et al, 2004). Perception of effort is also investigated during isolated motor tasks involving the upper or lower limb, in strength training program (Miller et al, 2009;Zourdos et al, 2016), in studies aiming at better understanding the regulation of endurance performance (Maikala & Bhambhani, 2006;Pageaux et al, 2013) or the mechanisms associated with the development of muscle fatigue during repetitive tasks Jacquet et al, 2021;Otto et al, 2019;Yang et al, 2019). To the best of our knowledge, most of the studies investigating perception of effort are performed during locomotor exercises or isolated exercises performed with the lower limbs (de Morree et al, 2014;Faelli et al, 2019;Luu et al, 2016;Meir et al, 2015).…”