UPDATE from my expert friend who is a PI for DMD research:
She stated that a 6MWT less than 350 meters is an indication that the child will be losing ambulatory status within a year or so (assuming the child is old enough to be on the downturn…this is usually around 10 years old). If the child’s walk distance is below 275-250 meters, that would signal imminent loss. She also added that a walk >500 meters is really stellar for DMD 🙂
So, for the most part, similar to what McDonald et al. found.