The nature of the loss of strength and dexterity in the upper limb following stroke

People who had suffered a stroke within the previous two years were tested for strength, dexterity and the ability to generate fast movements of their affected elbow and compared to age-matched controls. Strength was measured via the joint torque generated during a maximal isometric contraction of the elbow flexors and extensors. Dexterity was assessed separately from strength by a tracking task that required skilled interaction of elbow joint flexors and extensors at two speeds - slow and fast. This task was set up so that very little strength was required to perform the task. Additionally, the ability to generate fast movements was measured by requiring subjects to flex and extend their elbow as fast as they could. Performance of the tracking task deteriorated at the faster speed in all subjects, however, this effect was more pronounced following stroke. In the stroke subjects, strength was poorly correlated with dexterity. Generally, stroke subjects could and did move their elbows in flexion and extension faster than was required to follow the targets. Poor performance of the stroke subjects on the tracking task was, therefore, the result of poor muscle control - a separate entity from strength. The results of this study indicate that weakness and loss of dexterity following stroke are separate problems, both of which may contribute to the slowness of movement seen in the clinic.