Overview
Shadowboxing is a combat sport exercise in which a person throws punches at the air as though there is an opponent. Practised primarily in boxing, it is used mainly to prepare the muscles before the person training engages in stronger physical activity. Muhammad Ali once performed a now famous shadowboxing routine next to Howard Cosell for ABC's Wide World of Sports television cameras. Black Nova Scotian boxer George Dixon is widely credited for developing the technique.
Details
Most boxing trainers prefer that their fighters do their shadow boxing before engaging in any other daily exercise routines. The main purpose of this exercise, apart from getting the muscles ready for another activity, is usually to maintain a fighter's rhythm and show the fighter how they would look at that stage of training against a certain opponent. This could be important as fighters envision themselves facing their immediate future opponents: it usually gives fighters an idea of what is, and what is not, to be fixed. It is also beneficial to sometimes incorporate dumbbells' as you shadow box so punches can flow quicker without them. It is also good to look in a mirror as you shadowbox so you can catch slight errors in your rhythm.
Fighters may want to do some shadowboxing of their own after their daily routines are over, either inside a boxing gym's ring, or wherever they please to at home without having to look directly at a mirror.
Each boxing round is 3 minutes and you should not really stop during this workout/routine. Shadowboxing is all about flowing offensively and defensively and it is also important to not throw full punches all the time, it can drain you out before the actual training starts. Once you get the rhythm down then you picture yourself in the fight and react to your invisible opponent.
From Wikipedia (CC BY-SA 4.0).