I agree this is a little silly, but I think the problem is not with the injuries, but with how they represent the different training sessions. They should just be called 'light training', 'medium training' and 'heavy training'. They all do the same thing, so if you changed injuries to be consistent with the type of training, to play optimally you would need to log in every 10 minutes to do stretching and never do the others at all. I'm pretty sure people don't want that.