Spinal and supraspinal mechanisms affecting torque development at different joint angles.
BACKGROUND
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.
UMR7287, CNRS, Aix-Marseille University, 163 avenue de Luminy, 13288, Marseille, France.
Maria
M
Papaiordanidou
UMR7287, CNRS, Aix-Marseille University, 163 avenue de Luminy, 13288, Marseille, France.
Valérie
V
Mustacchi
UMR7287, CNRS, Aix-Marseille University, 163 avenue de Luminy, 13288, Marseille, France.
Jean-Damien
JD
Stevenot
UMR7287, CNRS, Aix-Marseille University, 163 avenue de Luminy, 13288, Marseille, France.
Michele
M
Vanoncini
INSERM U1093 Cognition, Action et Plasticité Sensorimotrice, Université de Bourgogne, UFR STAPS, Campus Universitaire, Dijon, France.
Alain
A
Martin
D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque; D055815:Young Adult
electromyography; muscle mechanical properties; neural activation; spinal excitability; twitch interpolation