Intra‐rater Reliability of Arm and Hand Muscle Strength Measurements in Persons With Late Effects of Polio

BACKGROUND: Muscle weakness in the upper limb is common in persons with late effects of polio. To be able to measure muscle strength and follow changes over time, reliable measurements are needed. OBJECTIVE: To evaluate the intra-rater reliability of isometric and isokinetic arm and hand muscle strength measurements in persons with late effects of polio. DESIGN: A test-retest design. SETTINGS: A university hospital outpatient clinic. PARTICIPANTS: Twenty-eight persons (mean age 68 years, SD 11 years) with late effects of polio in their upper limbs. METHODS: Isometric shoulder abduction, isokinetic concentric elbow flexion and extension, isometric elbow flexion, and isometric grip strength were measured twice, 14 days apart. Reliability was evaluated with the intra-class correlation coefficient, the mean difference between the test sessions (d¯), together with the 95% confidence intervals for d¯ , the standard error of measurement (SEM and SEM%), the smallest real difference (SRD and SRD%), and Bland-Altman graphs. MAIN OUTCOME MEASUREMENTS: A fixed dynamometer (Biodex) was used to measure arm strength and an electronic dynamometer (GRIP-it) was used to measure grip strength. RESULTS: Intra-rater reliability was high, with intra-class correlation coefficients between 0.87 and 0.98. The SEM%, representing the smallest change for a group of persons, ranged from 7%-24% for all strength measurements, and the SRD%, representing the smallest change for an individual person, ranged from 20%-67%. CONCLUSION: Muscle strength in the upper limbs can be reliably measured in persons with late effects of polio. However, the measurement errors indicate that the method is more suitable to detect changes in muscle strength for a group of persons than for an individual person.