Regulating spinal motion requires proprioceptive feedback. While studies have investigated the sensing of static lumbar postures, few have investigated sensing lumbar movement speed. In this study, proprioceptive contributions to lateral trunk motion were examined during paraspinal muscle vibration. Seventeen healthy subjects performed lateral trunk flexion movements while lying prone with pelvis fixed. A 44.5-Hz vibratory stimulus was applied to the paraspinal muscles at the L3 level. Subjects attempted to match target paces of 9.5, 13.5, and 17.5 deg/s with and without paraspinal muscle vibration. Vibration of the paraspinal musculature was found to result in slower overall lateral flexion. This effect was found to have a greater influence in the difference of directional velocities with vibration applied to the left musculature. These changes reflect the sensitivity of lumbar velocity sense to applied vibration leading to the perception of faster muscle lengthening and ultimately resulting in slower movement velocities. This suggests that muscle spindle organs modulate the ability to sense velocity of motion and are important in the control of dynamic motion of the spine.
The authors are with the Human Motion Control Laboratory, Department of Mechanical Engineering, University of Kansas, Lawrence, KS.