My son has participated in cross country running from time to time but he says he dislikes it because he feels exhausted half way around the course.  I think that when your exerting yourself on that level as a CAH sufferer(which is a more long lasting demand on the body physically, sometimes exceeding 15 minutes or more)that there is perhaps more of a demand for cortisol.  Since there is no back up for it in the way of production from the adrenals in the amounts being demanded, it would make sense that fluids and electrolytes become more imbalanced than they would in a non CAH sufferer.  We know a guy in Canada that we are in touch with that  has CAH and he says he had the same problem as a child in sport.  He said he was far happier when he participated in the short distance sprints and was often more successful with those.  My son likes to play soccer, and I can see at times that although at the beginning he looks like he has the stamina (he runs very fast for his size and moves great), he does seem to flag 'energy wise' before a lot of the other boys on the feild.  

JH