P.2.10 A shorter timed walking or running test may be sufficient for testing function in Duchenne muscular dystrophy

Clinical trials involving exon skipping, gene transfer, and small molecule development are currently underway for children with Duchenne muscular dystrophy. These experimental trials typically use timed walking as the primary measure of efficacy due to ease of test administration, ability to quantify distance walked, and a body of literature investigating the reliability and validity of these walking outcomes. However, a test lasting 6-min has inherent difficulties when testing young children in clinical trials. Ambulatory subjects with DMD (5–12 years old; mean = 9.6 ± 2.1 years) completed timed walking tests, strength testing, the North Star Ambulatory Assessment (NSAA), and timed 4 stairs. The 6-min walk test (6MWT) was compared to two shorter ambulatory assessments: 2-min walk test (2MWT), and 100 m walk/run test (100 m). The 2MWT was completed according to 6MWT guidelines but lasted only 2-min; whereas the 100 m allowed subjects to complete two 50-m laps as quickly as possible, including running if able. Maximum voluntary isometric strength of hip and knee muscles was assessed using a hand-held dynamometer. The 2MWT and 100 m were highly correlated with 6MWT ( r = 0.827 and r = −0.827 respectively, p = 0.002). The 100 m was most highly correlated with lower extremity strength measures and other functional outcomes. A shorter timed walking or running test may be beneficial for use in clinical trials in children with Duchenne muscular dystrophy. The 2MWT or 100 m may decrease individual variability seen in the 6MWT due to shorter walking time or a concrete fixed distance. Further research is needed to determine which ambulatory assessments are most valid, reliable, and sensitive to change over time.