Article

Individuals with incomplete spinal cord injury (SCI) are predisposed
to muscle fatigue during voluntary exercise. However, the origin of fatigue is
unclear. OBJECTIVE: The authors examined the motoneuron excitability, muscle
activation level, and fatigue properties of the flexor carpi radialis muscle,
just below the level of injury. METHODS: Nine individuals with chronic,
incomplete cervical cord injury and 9 age-matched healthy individuals were
recruited. The authors tested maximum voluntary contraction (MVC), motoneuron
excitability by the maximum amplitude of the H-reflex (Hmax at C-7), and muscle
voluntary activation level measured by the interpolated twitch technique.
Subjects were fatigued by repetitive maximal voluntary isometric wrist flexion.
General fatigue index (GFI), central fatigue index (CFI), and peripheral fatigue
index (PFI) of flexor carpi radialis were examined before, during, and
immediately after exercise. RESULTS: The Hmax in the SCI group was significantly
higher (P = .0028) than in controls. The MVC (P < .001) and voluntary activation
level (P = .016) in the SCI group were significantly lower. The GFI and CFI
decreased in both the SCI and the non-SCI groups. The PFI in the SCI group was
significantly higher (ie, less fatigue) than that in controls at 30 repetitive
contractions. CONCLUSIONS: In individuals with incomplete SCI, the deficit in
central drive is an important source of muscle weakness and fatigue in the muscle
below the level of injury.

Langue : ANGLAIS