Passive Mechanical Properties of Gastrocnemius Muscles of People With Ankle Contracture After Stroke

Kwah LK, Herbert RD, Harvey LA, Diong J, Clarke JL, Martin JH, Clarke EC, Hoang PD, Bilston LE, Gandevia SC. Passive mechanical properties of gastrocnemius muscles of people with ankle contracture after stroke.ObjectiveTo investigate the mechanisms of contracture after stroke by comparing passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in people with ankle contracture after stroke with control participants.DesignCross-sectional study.SettingLaboratory in a research institution.ParticipantsA convenience sample of people with ankle contracture after stroke (n=20) and able-bodied control subjects (n=30).InterventionsNot applicable.Main Outcome MeasuresStiffness and lengths of gastrocnemius muscle-tendon units, lengths of muscle fascicles, and tendons at specific tensions.ResultsAt a tension of 100N, the gastrocnemius muscle-tendon unit was significantly shorter in participants with stroke (mean, 436mm) than in able-bodied control participants (mean, 444mm; difference, 8mm; 95% confidence interval [CI], 0.2–15mm; P=.04). Muscle fascicles were also shorter in the stroke group (mean, 44mm) than in the control group (mean, 50mm; difference, 6mm; 95% CI, 1–12mm; P=.03). There were no significant differences between groups in the mean stiffness or length of the muscle-tendon units and fascicles at low tension, or in the mean length of the tendons at any tension.ConclusionsPeople with ankle contracture after stroke have shorter gastrocnemius muscle-tendon units and muscle fascicles than control participants at high tension. This difference is not apparent at low tension.