This doesn't mean that MyFitnessPal is in trouble -- go to the iOS App Store and you'll still find that it's one of the top health apps. However, it does complicate Under Armour's efforts to become a one-stop fitness shop. The company is counting on activity tracking apps like MyFitnessPal and Endomondo as the glue that keeps its strategy together, and it now has to hunt for replacements that will not only preserve what the Lees accomplished, but keep their app relevant for years.