According to this news story, it can inhibit potassium levels, which along with calcium aids in relaxing and tensing the muscle. This is why potassium and calcium are usually the only minerals added to sports drinks.
Low potassium levels seem to cause a number of other serious maladies. The article isn't that in-depth but "The author of the research paper, Dr Moses Elisaf from the University of Ioannina in Greece, said it appeared that hypokalaemia can be caused by excessive consumption of three of the most common ingredients in cola drinks - glucose, fructose and caffeine."
Glucose, fructose and caffeine are substances that its easy to over-do if bulking on junk food, so this has some ramifications on those of us who consider soda a useful source of easy calories.
Have a read. Anybody know any more about this?
Good thing I only drink diet soda
But I'm totally screwed if caffeine inhibits muscle growth.