Fast walking velocity in health and Duchenne muscular dystrophy: a statistical analysis.

Fast walking velocity was measured in 335 apparently healthy subjects, 180 males and 155 females, whose ages ranged from 3.5 to 24 years. These velocities increased with age and approached an asymptote of 3.44m/sec in males and 3.17 m/sec in females, a statistically significant difference (p less than 0.001). This parameter was also measured serially over periods of 18 to 132 months in 15 patients with Duchenne muscular dystrophy. A decrease in walking rate began between ages four and six. This decline was found to fit linear and monoexponential decay mode models equally. Average linear decay for all 15 patients was 0.0308 m/sec/month; and the average fractional decay was 0.0349/month. On average, by 10 years, the fast walking rate was reduced to about 29% of normal. This measure of disease progression followed a unique course in each subject, which could be mathematically characterized by a unique decay rate, and a unique walking velocity at age 10 years. Thus, in contrast to natural speed walking, the measurement of fast walking velocity has proved to be a simple and useful index for characterizing disease progression in Duchenne muscular dystrophy, and for evaluating therapeutic interventions.