Effects of muscle thixotropy on spindle afferent activity in the hindlimb of the rat

The increase of the stiffness of a resting gastrocnemius muscle with time and its effect on afferent activity in the tibial nerve were investigated in the anesthetized rat. A sinusoidal torque from a motor coaxial with the ankle produced small oscillations of the resting foot that were interrupted by several cycles of a much larger amplitude displacement. After the perturbation, the same small torque caused larger oscillations, demonstrating a reduction in the resting or short-range stiffness of muscles acting at the joint. Afferent nerve activity in response to the small torque was greater following the perturbation, reflecting the larger oscillations.<>