The 6-minute walk test as a new outcome measure in Duchenne muscular dystrophy. 
Walking abnormalities are prominent in Duchenne muscular dystrophy (DMD).  We modified the 6-minute walk test (6MWT) for use as an outcome measure in patients with DMD and evaluated its performance in 21 ambulatory boys with DMD and 34 healthy boys, ages 4 to 12 years.  Boys with DMD were tested twice, approximately 1 week apart; controls were tested once.  The groups had similar age, height, and weight.  All tests were completed.  Boys who fell recovered rapidly from falls without injury.  Mean +/- SD [range] 6-minute walk distance (6MWD) was lower in boys with DMD than in controls (366 +/- 83 [125-481] m vs. 621 +/- 68 [479-754] m; P < 0.0001; unpaired t-test).  Test-retest correlation for boys with DMD was high (r = 0.91).  Stride length (R(2) = 0.89; P < 0.0001) was the major determinant of 6MWD for both boys with DMD and controls.  A modified 6MWT is feasible and safe, documents disease-related limitations on ambulation, is reproducible, and offers a new outcome measure for DMD natural history and therapeutic trials.