Effects of Neuromuscular Fatigue on Hierarchical Control and Motor Synergies

Open Access
Singh, Tarkeshwar
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
April 26, 2012
Committee Members:
  • Mark Latash, Dissertation Advisor
  • Mark Latash, Committee Chair
  • Vladimir M Zatsiorsky, Dissertation Advisor
  • Jinger Gottschall, Committee Member
  • Arkady Tempelman, Committee Member
  • Fatigue
  • synergies
  • motor coordination
  • motor control
  • grasping
  • prehension
Muscle fatigue leads to changes at many levels of the neuromotor hierarchy. Some of these changes are adaptive, that is they try to alleviate effects of fatigue on performance. Several earlier studies have shown that, if a motor task involves a redundant set of elements, goal-relevant features of performance are relatively preserved during neuromuscular fatigue of one (or a few) of the elements. In the series of studies presented in this dissertation a hypothesis has been tested that fatigue increases the co-variation within redundant sets of elements in order to preserve the goal-relevant features of performance. The results from the first three experiments included in this dissertation show that fatigue of one of the elements within a redundant system leads to increased variability of both exercised and non-exercised elements. This is associated with an increase in the indices of motor synergies stabilizing task-related performance variables. These findings have been confirmed in multi-finger accurate force production tasks and multi-muscle accurate sway tasks. Another issue addressed in this dissertation is the effects of fatigue in a hierarchically organized motor system. The fourth study looked at the effects of fatigue on the motor synergies of the ipsilateral (exercised) and contralateral (non-exercised) hand in accurate force production tasks. We found an increase in the indices of motor synergies stabilizing task-related performance variables in the ipsilateral as well as the contralateral hand. The last study in this dissertation investigated the effects of thumb and index finger fatigue in a static prehension task. We did not find any effects of fatigue in motor synergies stabilizing the main performance variables, but the force and moment output of the individual digits changed to keep the grasped object in static equilibrium. We conclude that fatigue of an element within a redundant system may lead to increased indices of synergies stabilizing important performance variables. These effects may be task dependent; in particular, they may vary depending on the hierarchy of control levels involved in the task.