Boxing as a form of fitness

Assalamu Alaykum I've done some searching and so far have not found an opinion on boxing for fitness within Islam. I've found that I am sound wrestler and have been looking for alternative means of training my stamina before I start lifting weights. When I say boxing for fitness, the general idea I have is not to go to a boxing gym and fight but rather to train using boxing methods i.e.(skipping, using punching bags and shadow boxing) as it is much more intense training than that of wrestling. I have absolutely no intention to even spar within the gym let alone fight. I would very much appreciate an opinion on this. Jazakallah