The significance of proprioception on postural stabilization as assessed by ischemia.

In order to further investigate the role of proprioceptive input from the legs for the maintenance of upright human posture ischemia was bilaterally applied at the level of the ankle or the thigh. Preservation of efferent innervation was ascertained by measurements of the maximal force of voluntary dorsi- and plantarflexion. Visual stabilization was excluded by eye closure. To test different frequency domains of postural stabilization, subjects were exposed to sudden ramp tilts or to sinusoidal low frequency (0.3 Hz) anteriorposterior displacements of the supporting platform. The results indicate that proprioceptive input from skin, pressure and joint receptors of the foot (ischemia at the ankle) is of minor importance for the compensation of rapid displacements, but plays a significant role when the platform moves at low frequencies. M1 and M2 responses in the stretched triceps surae and the late antagonistic response of the anterior tibial muscle (M3) are preserved with ischemia of the foot. Reversible ischemic paralysis or other (yet unidentified) mechanisms of destabilization must be responsible for the severe decrease of postural stability observed with ischemia at the level of the thigh and sinusoidal platform movements. Complete loss of the proprioceptive input from the legs leads to a pathognomonic 1Hz body tremor both under static and dynamic conditions.