Muscle weakness in Parkinson's disease: isokinetic study of the lower limbs.

Isokinetic strength of knee extension and flexion was measured at two speeds of movement in 23 patients with Parkinson's disease, to clarify whether muscle weakness is inherent to the disease. To counteract normal variation among subjects, we selected patients with symptoms completely or largely confined to one side and compared sides for each patient. The affected side was weaker than the other in both slow and fast movements early in the disease. In more advanced disease, the difference between sides diminished at the slow speed but remained significant at the faster speed. These observations suggest that weakness is inherent to Parkinson's disease and influenced by movement speed.