Abstract
While the use of motor imagery (the mental representation of an action without overt execution) during actual training sessions is usually recommended, experimental studies examining the effect of physical fatigue on subsequent motor imagery performance are sparse and yielded divergent findings. Here, we investigated whether physical fatigue occurring during an intense sport training session affected motor imagery ability. Twelve swimmers (nine males, mean age 15.5 years) conducted a 45 min physically-fatiguing protocol where they swam from 70% to 100% of their maximal aerobic speed. We tested motor imagery ability immediately before and after fatigue state. Participants randomly imagined performing a swim turn using internal and external visual imagery. Self-reports ratings, imagery times and electrodermal responses, an index of alertness from the autonomic nervous system, were the dependent variables. Self-reports ratings indicated that participants did not encounter difficulty when performing motor imagery after fatigue. However, motor imagery times were significantly shortened during posttest compared to both pretest and actual turn times, thus indicating reduced timing accuracy. Looking at the selective effect of physical fatigue on external visual imagery did not reveal any difference before and after fatigue, whereas significantly shorter imagined times and electrodermal responses (respectively 15% and 48% decrease, p<0.001) were observed during the posttest for internal visual imagery. A significant correlation (r = 0.64; p<0.05) was observed between motor imagery vividness (estimated through imagery questionnaire) and autonomic responses during motor imagery after fatigue. These data support that unlike local muscle fatigue, physical fatigue occurring during intense sport training sessions is likely to affect motor imagery accuracy. These results might be explained by the updating of the internal representation of the motor sequence, due to temporary feedback originating from actual motor practice under fatigue. These findings provide insights to the co-dependent relationship between mental and motor processes.
Highlights
Motor imagery (MI) is the mental simulation of an action without any associated overt movement
MI elicits comparable autonomic responses to those observed during PP [5,6], while both EMG and TMS correlates of MI concur to support that the somatic motor command might be programmed during MI [7,8]
Central and peripheral neurophysiological correlates of MI support that it should not be artificially decoupled from the action itself, but rather be placed along a continuum extending from the overt movement to its mental representation [10]
Summary
Motor imagery (MI) is the mental simulation of an action without any associated overt movement. Holmes and Collins [19] suggested that since MI shares the same central processes as actual motor planning and programming, most components of PP should be reproduced during MI This theoretical stance supports most recommendations for MI use to improve motor performance, like performing MI in an environmental context matching PP conditions [20,21] and preserving the spatio-temporal characteristics of actual movement [22]. Several models were designed to promote the best rules for MI practice In their well-known PETTLEP model (Physical, Environment, Task, Timing, Learning, Emotion, and Perspective), Holmes and Collins [19] provided a detailed description of the key-components that should be considered to ascertain MI efficacy. They reported that mental fatigue might occur rapidly during mental training, and that MI sessions might benefit from limited successive trials [14,27,28]
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