Well because when ur eyes are open for a while the eye gets used to it so when u close it it hurts
Baseball let’s say they are on off season they train with there team it batting cages and in and off the field for practice and also to stay in shape?
I do believe it's all of the above. Although, it might not be trouble sleeping. That might be true in some cases, but not in all.
You have to have a goal before you work out or should so d would be the answer