Movement velocity dependent muscle strength in Parkinson's disease

We measured isokinetic muscle strength of knee extension and flexion in 18 patients with Parkinson's disease who showed marked laterality in symptom severity and compared strength between the sides in the same patient. In all patient groups, the maximum peak torque of the more affected side was significantly less than for the less affected side at 15 revolutions per minute (r.p.m.) and 30 r.p.m. with the difference between the sides being larger at 30 r.p.m. than at 15 r.p.m., while at 5 r.p.m. there were no significant differences between sides. In the Yahr stage I group, the maximum peak torque in both extension and flexion at each velocity showed no significant difference between the sides. In contrast, in the stage II and III groups the maximum peak torque at 5 r.p.m. showed no significant difference between the sides, while at 15 r.p.m. and 30 r.p.m. these values showed a tendency and a significant difference between the sides, respectively, with the more affected side being weaker. These results suggest that muscle weakness in patients with Parkinson's disease increases with performance velocity, especially as the disease progresses.