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Neural Mechanisms of Task Failure During Sustained Submaximal Contractions

Williams, Petra S.
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1367330801

Abstract Details

2013, Doctor of Philosophy (PhD), Ohio University, Biological Sciences (Arts and Sciences).
Fatigue is an expected and normal physiologic reaction to intense and to sustained activity. As fatigue develops during sustained isometric submaximal contractions, the amount of excitatory descending drive from supraspinal regions to the spinal motorneuron pool increases to compensate for the decline in spinal excitability by recruiting additional motor units in order to prolong task performance. However, despite the compensatory mechanisms from supraspinal inputs, task failure remains inevitable. Therefore, it remains largely unknown whether supraspinal mechanisms that could alter the amount of descending drive, including changes in motor cortex excitability and voluntary drive upstream to the motor cortex, also contribute to task failure. The focus of this dissertation research was to delineate the specific contributions that supraspinal circuits have in determining the time to task failure. Experiment 1 compared adjustments in multiple neurophysiologic measures of supraspinal and spinal excitability taken throughout the performance of two different fatigue tasks (i.e. force-matching and position-matching) to determine the functional significance of the changes to task duration. Although no task-specific differences were found, task failure occurred for both tasks after a similar mean decline in motorneuron excitability developed coupled with a similar mean increase in corticospinal excitability. Additionally, the amount of intracortical inhibition dropped while the amount of intracortical facilitation and upstream excitation of the motor cortex remained unchanged. Together the data for these two tasks indicate that, in general, the motor cortex is able to compensate for changes in spinal excitability until a critical amount of change in both regions develops. This suggests that unless more drive is provided to the motor cortex to sustain or strengthen the descending drive, failure occurs. Experiment 2 examined whether delivering anodal transcranial direct current stimulation (tDCS), a non-invasive neurostimulation known to transiently increase cortical excitability, to the motor cortex during the performance of a sustained submaximal contraction would increase task duration compared to a sham tDCS condition. Anodal tDCS increased the time to task failure by more than 30% and also increased the amount of muscle fatigue by 6% in individuals whose time to task failure occurred prior to the termination of the anodal stimulation. Additionally, the stimulation increased the duration of time that the subjects were able to exert a high amount effort. These finding suggests that the anodal tDCS provided the additional excitatory input to the motor cortex needed when task failure was eminent in order to overcome the increase in spinal resistance that could not otherwise be met by volitional drive. Together the results from these two experiments provide complimentary evidence to support the conclusion that the capacity of supraspinal inputs to endlessly override the decline in spinal motorneuron excitability is eventually limited by the failure to increase intracortical facilitation as well as upstream drive delivered to the motor cortex and not the development of intracortical inhibition. The experience of fatigue in healthy populations is both physical and perceptual; however the clinical symptom of perceived fatigue may not be associated with changes in motor performance. The application of these findings to clinical examination and treatment of physical performance fatigue and the symptom of perceived fatigue will benefit from both clinical research as well as further research into the mechanisms of tDCS induced enhancements in task performance and also into the mechanisms behind the difference in time to task failure for the force-matching and position-matching tasks.
Brian Clark, PhD (Advisor)
Thad Wilson, PhD (Committee Member)
Robert Staron, PhD (Committee Member)
Roger Gilders, PhD (Committee Chair)
246 p.
Neurology; Neurosciences; Physiology; Rehabilitation
neural mechanisms of fatigue; sustained submaximal contractions; transcranial direct current stimulation tDCS; transcranial magnetic stimulation TMS; cervicomedullary evoked potentials CMEP; supraspinal mechanisms of fatigue

Recommended Citations

Citations

  • Williams, P. S. (2013). Neural Mechanisms of Task Failure During Sustained Submaximal Contractions [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1367330801

    APA Style (7th edition)

  • Williams, Petra. Neural Mechanisms of Task Failure During Sustained Submaximal Contractions. 2013. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1367330801.

    MLA Style (8th edition)

  • Williams, Petra. "Neural Mechanisms of Task Failure During Sustained Submaximal Contractions." Doctoral dissertation, Ohio University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1367330801

    Chicago Manual of Style (17th edition)

ohiou1367330801
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© 2013, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.