The effect of antagonist muscle co-contraction on damping of the wrist joint during voluntary movement

Damping characteristics of the musculoskeletal system were investigated during rapid voluntary wrist flexion movements. Oscillations about the final position were induced by coupling the wrist to a load which had the characteristics of negative viscosity. The greater the negative viscosity of the load, the greater the observed co-contraction of wrist flexor and extensor muscles. While wrist stiffness increased in parallel with the increased co-contraction, wrist viscosity varied in a more complex manner that appeared to depend on both velocity of oscillation and reflex force produced by muscle stretch.