Backgrounds: The cause of the postural instability of Parkinson´s disease is unknown.
Methods: We have investigated postural control in thirty ambulatory idiopathic parkinsonian patients. Body sway, torque, and force exerted by each foot, and electromyographic activity of anterior tibial, gastrocnemius, quadriceps, hamstring, rectus abdominis, and paraspinal muscles were recorded following forward and backward perturbations on a moveable platform.
Results: Normal subjects of old age responded to platform perturbations by either of two strategies: activation of muscles in a distal to proximal sequence to correct body sway by movement at the ankle(ankle strategy), or activation of muscles proximal to distally to maintain balance by hip movement(hip strategy). In the parkinsonian patients, platform perturbations elicited simultaneous activation of the mu scles in the ankle and hip strategies, in effect, counteracting the corrective response that would be- produced by either strategy in isolation. The latencies and magnitudes of the reponses were normal.
Conclusion: The postural instability of these patients with Parkinson´s disease did not result from slow or weak postural responses of leg muscles, but rather, from an inappropriate pattern of activation of leg and truncal muscles.
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