Question

A boxer can punch a heavy bag for more than an hour without tiring, but will tire quickly when boxing with an opponent for a few minutes. Why? (Hint: When the boxer's fist is aimed at the bag, what supplies the impulse to stop the punches? When the boxer's fist is aimed at the opponent, what or who supplies the impulse to stop the punches that don't connect?)

Answer 1

“Not only the above but also a heavy bag doesn't move, depending on your style you may end up chasing or running away a lot during a match.

The heavy bag is just punching with a little movement here and there in the ring your work rate has to be much higher otherwise your doomed.

Plus when you take punches that can fatigue you.”

honestly found this on yahoo answers lol, hope this helps!!