Assessment of muscle strength in Duchenne muscular dystrophy.

Muscle strength in 23 patients with Duchenne dystrophy was tested against gravity and manual resistance during an 8-year period. The data show striking linearity in rate of loss of strength with age for any given patient. The tempo does not appear altered during growth spurts, bracing, or loss of ambulation. Variability in disease severity was documented clearly by 7 years of age and appears to be related to earlier age at onset of symptoms. This long ignored method of muscle strength assessment provides a precise measure of disease progression and, since the technique is widely used by physical therapists, it should be incorporated in clinical studies and therapeutic trials.