a) Fat ( green) an d water (red) fusion images of the abdominal and expiratory muscles of a 16 yr old unaffected control, an ambulatory 13 yr old with DMD, and a nonambulatory 16 yr old with DMD. Significant fatty infiltration of the expiratory muscles is visible in the individuals with DMD, and early involvement of the internal oblique was consistently seen even in ambulatory participants. b) Fat fraction (FF) was elevated in DMD compared to controls for each expiratory muscle analyzed. The rectus abdominis was, on average, the least affected expiratory muscle, while the internal oblique was the most affected. c) Internal oblique FF increased with increasing age (r=0.67, p<0.001). d) Internal oblique FF was significantly correlated with percent predicted maximal expiratory pressure (%pMEP) (r=−0.70, p<0.001). *Indicates p<0.05