Isokinetic knee extension and flexion strength in individuals with hemiparesis after stroke

The aim of this study was to assess knee extensor and flexor muscle torque in individuals with hemiparesis after stroke and determine the relationship with muscle tone. Fifty individuals (mean age 58 +/- 6.4 years), 6 to 48 months after stroke, participated in the study. Maximal concentric knee extension and flexion torque at 60 degrees/s and 120 degrees/s and maximal eccentric knee extension contractions at 60 degrees/s were measured with a Biodex dynamometer. Muscle tone was assessed with the modified Ashworth Scale. The relative weakness in the paretic knee muscles ranged from 30% to 42% and was greater for the flexors and at higher velocities (p < 0.05). The knee flexion/extension torque ratio in the non-paretic lower limb was 0.53 for both velocities and significantly lower (p < 0.01) for the paretic lower limb (0.44 at 60 degrees/s and 0.39 at 120 degrees/s). The eccentric/concentric ratio in the paretic lower limb (1.66) was significantly higher (p < 0.05) than in the non-paretic lower limb (1.31). Concentric torque in the paretic lower limb was significantly correlated (p < 0.05) with muscle tone. In conclusion, post-stroke weakness of the knee muscles was most prominent in the flexors and at higher velocities, whereas eccentric strength seemed to be preserved. Strength was also associated with the spasticity that can occur after stroke. This post-stroke muscle weakness pattern could be of importance for gait performance and should therefore be accommodated when planning rehabilitation interventions.