Again too smart by half. Some study finds that low intensity exercise causes fast twitch to atrophy and nutrition majors and guys with GEDs and certs take the ball and run with it. No, low intensity exercise only causes the fast twitch fibers to atrophy because they are not being used. If you train your fast twitch fibers they wont atrophy. Then you hear but but cortisol is released during aerobic exercise and that causes catobolism. Yes cortisol is released whenever you work out. The how much is released depends on the intensity of the workout. anaerobic exercise releases more cortisol than aerobic.
atsch Boxing has peaks and valleys where marathon running is usualy at the same pace, running 100 meters fast, 100 meter walk, 100 meter jog, then 100 meter 100 meter mix, is a better reflection of boxing, you won't tire out too much and can keep up with unusually pace increases. If you run marathon it is good but you need short term endurance. Marathon is stressful on your heart and joints. You don't want to be running 26 miles, just run 3-10 max. Running long distances would be better for a heavyweight as most have no endurance. A 200 pound guy who can run for 45 minutes at a decent pace would probably clean house by just dancing for 4 rounds and beating his opponent down. Most heavyweights can't keep the pace that welters fight for more than 3-4 rounds before falling over each other.