Why punch a boxing bag?
It can improve your reflexes. This may enable you to catch your favourite wine glass if you accidently knock it off the sink. And can enable you to avoid objects hurtling towards you.
It can increase your heart rate. This can then improve your respiratory circulation and your coronary circulation. Thus, if you have good nutrition in your body this circulation will distribute all the goodies to hungry and eager body cells.
Hitting the bag with your bony little mitt can increase the density of your bones. This will increase your capacity to resist injury in event of a fall or accident.
Thus by punching the bag…..you get to feel better.
Punch bags, not people.