Intrarater reliability of manual muscle test (Medical Research Council scale) grades in Duchenne's muscular dystrophy

The purpose of this study was to document the intrarater reliability of manual muscle test (MMT) grades in assessing muscle strength in patients with Duchenne's muscular dystrophy (DMD). Subjects were 102 boys, aged 5 to 15 years, who were participating in a double-blind, multicenter trial to document the effects of prednisone on muscle strength in patients with DMD. Four physical therapists participated in the study. Two identical (duplicate) evaluations were performed within 5 days of each other by the same examiner initially and after 6 and 12 months of treatment. A total of 18 muscle groups were tested on each patient, 16 of them bilaterally, using a modification of the Medical Research Council scale. Reliability of muscle strength grades obtained for individual muscle groups and of individual muscle strength grades was analyzed using Cohen's weighted Kappa. The reliability of grades for individual muscle groups ranged from .65 to .93, with the proximal muscles having the higher reliability values. The reliability of individual muscle strength grades ranged from .80 to .99, with those in the gravity-eliminated range scoring the highest. We conclude the MMT grades are reliable for assessing muscle strength in boys with DMD when consecutive evaluations are performed by the same physical therapist.