Not all boxers do, but those that train early in the mornings do it for some of the following reasons:
morning jog
It is bad because your body is still waking up.
Yes it is good to jog in the morning.
It is "in the morning." For example, "I like to go for a jog in the morning."
No. In the fist place, it would be the infinitive use, not the past used: did you use to jog. But the idiom doesn't like being treated that way. We say Did you jog in the morning.
ride bikes swim jog smile
set a alarm clock
Early Morning Dream was created in 1972.
Early Morning Rain was created in 1964.
Early Christmas Morning was created in 1998.
Early Sunday Morning was created in 1930.
Early Morning Hymns was created in 2004.