Spinal and supraspinal mechanisms affecting torque development at different joint angles

• Papaiordanidou Maria
• Mustacchi Valérie
• Stevenot Jean-Damien
• Vanoncini Michele
• Martin Alain

• Spinal excitability
• Twitch interpolation
• Electromyography
• Muscle mechanical properties
• Neural activation

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.