are like oil and water. Strength training tightens tendons and you need loose tendons for quicker reaction and snap on your punches. Any strength training for your upper body will effect your speed, power, endurance, and timing. I dont even recommend swimming. Anything for legs or abs are good. Other then that stick to sprinting, long jogs over 30 mins to burn muscle and fat, anything boxing related as far as sparring, mitts, bags, jump rope.
Yep, I I kind agree. Its an old school approach but works. Adding a dynamic flexibility routine has massive benefits to a fighters training if not already in a fighters routine. Increased range of motion etc