RESUMEN
The North Star Ambulatory Assessment measures motor performance in ambulatory boys with Duchenne muscular dystrophy, a hereditary and degenerative muscle disorder. To use the North Star Ambulatory Assessment in Brazilian boys, we performed the cross-cultural adaptation to the Portuguese language spoken in Brazil and evaluated the reliability and validity of the instrument. Cross-cultural adaptation included: independent translations, synthesis, committee review, pre-testing in 12 boys, back-translation and comparison with the original instrument. Thirty-five boys with Duchenne muscular dystrophy and 38 healthy age-matched controls were recruited for further analyses. Reliability was assessed by internal consistency and reproducibility. Validity studies included face, content, construct and known-groups analyses. Cross-cultural adaptation resulted in an adequate instrument. Reliability studies demonstrated high internal consistency (Cronbach's alpha = 0.935) and adequate intra and inter-rater reproducibility (intraclass correlation coefficient = 0.988 and 0.962). Validation analyses indicated satisfactory content, face and convergent construct validities, with positive correlations with the Motor Function Measure total score (r = 0.863) and the 6-minute walk test (r = 0.433). The known group validity was demonstrated by higher scores in younger boys with Duchenne muscular dystrophy (p = 0.005). North Star Ambulatory Assessment in Brazilian Portuguese is a reliable and valid instrument to measure functional capacity in boys with Duchenne muscular dystrophy.