Article

Substantial data indicate greater muscle fatigue in individuals with
spinal cord injury (SCI) compared with healthy control subjects when tested by
using electrical stimulation protocols. Few studies have investigated the extent
of volitional fatigue in motor incomplete SCI. METHODS: Repeated, maximal
volitional effort (MVE) isometric contractions of the knee extensors (KE) were
performed in 14 subjects with a motor incomplete SCI and in 10 intact subjects.
Subjects performed 20 repeated, intermittent MVEs (5 seconds contraction/5
seconds rest) with KE torques and thigh electromyographic (EMG) activity
recorded. RESULTS: Peak KE torques declined to 64% of baseline MVEs with repeated
efforts in control subjects. Conversely, subjects with SCI increased peak torques
during the first 5 contractions by 15%, with little evidence of fatigue after 20
repeated efforts. Increases in peak KE torques and the rate of torque increase
during the first 5 contractions were attributed primarily to increases in
quadriceps EMG activity, but not to decreased knee flexor co-activation. The
observed initial increases in peak torque were dependent on the subject's
volitional activation and were consistent on the same or different days,
indicating little contribution of learning or accommodation to the testing
conditions. Sustained MVEs did not elicit substantial increases in peak KE
torques as compared to repeated intermittent efforts. CONCLUSIONS: These data
revealed a marked divergence from expected results of increased fatigability in
subjects with SCI, and may be a result of complex interactions between mechanisms
underlying spastic motor activity and changes in intrinsic motoneuron properties.

Langue : ANGLAIS