Relative and absolute reliabilities of the myotonometric measurements of hemiparetic arms in patients with stroke

Objective: To investigate the relative and absolute reliabilities of the myotonometer. Design: Psychometric study. Setting: Three medical centers. Participants: Patients with stroke (N=61). Interventions: Not applicable. Main Outcome Measures: Muscle tone, elasticity, and stiffness of relaxed affected deltoid, triceps brachii, biceps brachii, extensor digitorum, flexor carpi radialis, and flexor carpi ulnaris were measured twice, 30 minutes apart, using the myotonometer. Intraclass correlation coefficient, a relative reliability index, was calculated for 3 muscular properties and for each muscle to examine the degree of consistency and agreement between the 2 test sessions. Absolute reliability indices, including the SEM, smallest real difference, and Bland-Altman limits of agreement, were used to quantify measurement errors and check systematic biases of the 2 test sessions. Results: The intraclass correlation coefficients were.83 to.95 for muscle tone, elasticity, and stiffness of all muscle groups. The SEM and the smallest real difference of muscle tone, elasticity, and stiffness of the biceps were the smallest among the 6 muscles tested. The Bland-Altman analyses showed no systematic bias between most of the repeated measurements. Compared with other muscles, biceps had narrower limits-of-agreement ranges, indicating that the myotonometric measurements of the biceps had higher stability and less variation over time. Conclusions: The myotonometer reliably measures muscular properties, with good relative and absolute reliabilities. These findings are useful for clinicians and researchers to assess muscle properties reliably and determine whether a real change has occurred in groups and on individual levels of patients with stroke.