• Thomas, Christine K (PI)

Project: Research project

Project Details


Use of neurophysiological techniques to examine the factors underlying
muscle weakness and fatigue after human spinal cord injury (SCI) can
provide the vital information needed to develop rational therapeutic
strategies for these muscles. Improved muscle function would lead to a
more independent lifestyle for that person and provide psychological,
economic and societal benefits. The overall objective of this project
is to examine mechanisms of force production and fatigue during voluntary
contractions of triceps brachii. Data obtained from people with chronic
and incomplete cervical SCI (termed SCIin) will be compared to that
obtained from able-bodied (control) subjects. Triceps brachii provides
an ideal muscle for study since many people with cervical SCI recover
limited triceps function, a muscle that is crucial for reaching
movements, pushing a wheelchair and weight transfer. Subjects are asked to voluntarily activate triceps brachii at various
intensities. We will electrically stimulate the brachial plexus and/or
radial nerve to artificially activate the triceps muscle. This approach
will yield information about peripheral conduction of triceps motor
axons, the electrical and mechanical correlates of the twitch and, when
combined with voluntary contractions, the extent of central drive to this
motoneuron pool. Central drive and conduction latency will be explored
further by using non-invasive magnetic stimulation of the motor cortex.
Comparisons between the voluntary and evoked forces will indicate the
fraction of muscle under voluntary control. In many cases motor unit
firing patterns (rate, variability) will be recorded with selective
needle electrodes, also useful for assessing muscle denervation.
Modulation of unit firing pattern by cortical stimulation will indicate
the influence of motor cortex on single motoneurons. Furthermore, this
approach will allow us to examine: 1) the CNS mechanisms governing force
production (recruitment, rate-coding) and fatigue; and 2) the mechanical
twitch associated with contraction of the motor units. The data obtained
will characterize the functional status of triceps brachii in SCIin
subjects for the first time. Thus, the neuromuscular consequences of
SCIin will be defined at or just below the level of injury, phenomena
largely unexplored. Evidence will be sought to show that muscle weakness
is primarily due to partial muscle paralysis, that motoneuron loss can
occur by direct damage, as well as trans-synaptic degeneration, and that
the neuromuscular adaptation which occurs in different subjects reflects
the nature of the injury. These subsets of SCIin individuals may best
respond to different rehabilitation therapies. Moreover, the sparse
interference pattern in most of the muscles after SCIin provides a unique
opportunity to follow the behavior of both low and high threshold motor
units during repeated submaximal or maximal voluntary contractions.
Careful comparisons of these data after specific neurological injury with
data from control subjects can add fundamental new information about the
interplay between recruitment and rate coding as mechanisms for motor
control. Furthermore, the database produced will provide a well
understood model of SCIin from which to test the effectiveness of
potential rehabilitation strategies.
Effective start/end date1/1/946/30/12


  • National Institutes of Health: $222,653.00
  • National Institutes of Health: $5,671.00
  • National Institutes of Health: $302,608.00
  • National Institutes of Health: $371,025.00
  • National Institutes of Health: $396,026.00
  • National Institutes of Health: $378,750.00
  • National Institutes of Health: $301,760.00
  • National Institutes of Health: $123,704.00
  • National Institutes of Health: $367,935.00
  • National Institutes of Health: $378,750.00
  • National Institutes of Health: $236,214.00
  • National Institutes of Health: $378,750.00
  • National Institutes of Health: $301,681.00


  • Medicine(all)
  • Neuroscience(all)


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