Effect of muscle length on strength and dexterity after stroke

Abstract

Objective: The effect of muscle length on strength and dexterity after stroke was investigated. The aim was to determine if poor function at a particular muscle length could be attributed solely to differential weakness at this joint angle or whether an additional problem of differential dexterity exists. Design: This descriptive research study measured elbow flexor and extensor strength as well as dexterity at three elbow joint angles: 30°, 60° and 90° flexion. Dexterity was measured independently of strength. Subjects: Fifteen (seven female, eight male) chronic stroke patients (mean age 67 years) who could actively flex and extend their affected elbow participated. Ten neurologically normal control subjects (mean age 67 years) acted as controls. Main outcome measures: Strength was measured as peak elbow flexor and extensor torque at three angles; and dexterity was measured as coherence for slow and fast tracking also at three angles. Results: Dexterity was not affected by muscle length but strength was and this finding was the same for both stroke and controls. While the magnitude of the torque-angle curves was not significantly different between stroke and controls, the shape of torque-angle curves was altered after stroke so that both the elbow flexors ( p < 0.05) and extensors ( p < 0.05) tested weaker in the testing position where they were shortest. Conclusion: Since there was no differential loss of dexterity, it appears that differential loss of strength, especially in the shortened range, may explain the clinical observation of poorer function at one muscle length than another after stroke. Specific training to strengthen the muscles in these ranges is therefore of clinical importance for rehabilitation.