Fastest way for fighters to increase fitness

There are many ways that fitness specialists have to increase fitness levels , however most don’t work for fighters. Fitness for fighters is different than fitness for normal athletes. The same methods used for triathlon , swimming , running, even wrestling and rugby are completely different to what is required for competitive level , boxing, mama and Muay Thai .
Some say why ???? Simple rhythm!!! There is no rhythm in fighting so all breathing and muscle exertion is irregular , and often exerted with high intensity , adrenalin , and in a split second as a result of your oppnant . Therefor you entire training needs to be based around this philosophy , or throw it out the window . Anything rhythm related is a fighters worst enemy .