I disagree that this is only for amatuers. Pros do shadow boxing all the time. Its all about getting your technique down on certain moves you need to do before you try it against someone else. its the same with pad/bag work.
Also if you shadow box with small hand weights in your hands you build up your punching speed alot. I usually use 3lb. hand weights and hold them above my forehead line, so I get used to keeping my hands up with that weight and while I'm sparring my hands won't drop down as much in the latter rounds.
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