Reliability of hand-held dynamometry and functional strength tests for the lower extremity in children with Cerebral Palsy

PURPOSE: To evaluate the intertester reliability of two methods for measuring lower-limb strength in children with cerebral palsy (CP). METHOD: Twenty-five subjects with CP (7-17 years of age) participated in this study. Lower-limb muscle strength was measured on 2 occasions using a Hand-held Dynamometer (HHD; break-method and make-method) and a 30-sec Repetition Maximum (RM) during three functional strength tests for the lower extremities. Reliability was measured using the intraclass correlation coefficients (ICCs), the standard error of measurement (SEM) and the coefficient of variation (CV). RESULTS: The intertester reliability of strength measurement using a HHD was questionable with ICC values ranging from 0.42-0.73 for the break-method, and from 0.49-0.82 for the make-method. The SEM and CV (%) values ranged from 27.9-58.9 and 22.2-35.3% for the break-method, and from 30.6-52.7 and 16.2-56.2% for make-method. The intertester reliability of strength measurement using the 30-sec RM was acceptable with ICC values ranging from 0.91 -0.96, and SEM and CV (%) values ranging from 1.1-2.6 and 10.9-39.9% for the functional exercises. CONCLUSION: The intertester reliability of measuring muscle strength of the lower extremities using a hand-held dynamometer is questionable. The intertester reliability of the 30-sec RM for the lower extremity is acceptable.