Post, M., Renken, R., & Zijdewind, I. (2006). Cortical activity during a sustained maximal contraction: An fMRI study. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 2007.

"Mechanisms underlying motor fatigue can be separated into factors residing within the muscle (peripheral fatigue) and factors within the central nervous system (central fatigue). Central aspects of fatigue can be studied with the use of “twitch interpolation”; that is electrical peripheral stimulation of the muscle during a maximal contraction. If the electrical stimulation resolves in a force increase, the subject is not activating his muscle maximally. We have designed an experimental set-up that enabled us to study the twitch interpolation within a MR- scanner environment."

This study investigated central processes during fatigue and related the results of twitch superimposition technique with fMRI-data. Right handed subjects (N = 12) performed a sustained maximal contraction of three minutes with the right index finger. Twitch interpolation was given to the index finger abductor (First Dorsal Interosseus; FDI) every 20 seconds. During the task, brain activation was measured with a 3T MRI scanner, in combination with force recordings. SPM2 was used to detect activated brain areas. Furthermore, the activity of the hand area in the contralateral precentral gyrus (region of interest analysis) was measured during the contraction. For comparison with the twitch superimposition data the mean activation over 20 seconds was calculated. Mean force was measured during the same period.

Maximal force declined during the contraction. Significantly activated brain areas during the fatiguing contractions were the sensorimotor cortex (SMC), cerebellum, and supplementary motor area (SMA). The region-of-interest analysis of the precentral gyrus revealed an increase in brain activity during the first part of the contraction, followed by a decline at the end of the contraction. Analysis of the superimposed twitches revealed that a large part of the fatigue was due to changes within in periphery. However, part of the force decline was caused by a decline in central drive [thought effort and focus].

Implication. Reduction in force production during fatiguing activities is due to actual fatigue and a lessening of mental effort to perform the activity. Thinking harder and more intently during exercise has the potential to slow performance decline during fatigue.

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