Spinal and supraspinal mechanisms affecting torque development at different joint angles
Résumé
INTRODUCTION:
We examined the neural mechanisms responsible for plantar flexion torque changes at different joint positions.
METHODS:
Nine subjects performed maximal voluntary contractions (MVC) at 6 ankle-knee angle combinations [3 ankle angles (dorsiflexion, anatomic position, plantar flexion) and 2 knee angles (flexion, full extension)]. Neural mechanisms were determined by V-wave, H-reflex (at rest and during MVC), and electromyography during MVC (RMS), normalized to the muscle compound action potential (V/Msup , Hmax /Mmax , Hsup /Msup and RMS/Msup ) and voluntary activation (VA), while muscle function was assessed by doublet amplitude.
RESULTS:
MVC and doublet amplitude were significantly lower at plantar flexion (P < 0.01), while VA was significantly lower at dorsiflexion and full knee extension (P < 0.05). V/Msup and RMS/Msup were significantly lower at knee extension (P < 0.01), while Hsup /Msup was not affected by joint angle.
CONCLUSIONS:
These results indicate that joint positions leading to muscle lengthening produce reduced neural drive, due mainly to supraspinal mechanisms.