I believe it would be a lot better if the training menu option was low, like 5, instead of whatever your energy level is. That way if you accidentally hit train instead of changing the number it won't use all your energy. This has happened to me a few times and it's frustrating.

This is an awkward one as it used to default to 1 but players then complained about it not just defaulting to the max since they tended to use all energy training.