Will cardio boxing, kickboxing, or Muay Thai decrease my muscle hypertrophy weight training effect?

Past certain level these goals will be quite conflicting. I believe everyone has their optimal body weight, for certain sports. For martial arts (especially the ones not involving grappling/wrestling) that optimal body weight will be quite low. Anything above that means just an excess luggage to carry around through all the rounds spent in the ring. And it doesn’t even matter whether it’s muscle or fat. Sure, muscle is a tissue that (as opposed to fat) actually does something (contracts) and you might think it would contribute to performance by giving you extra strength/power. However, muscle needs blood supply and much more of it than adipose tissue (fat) which means heart of the athlete needs to work harder.

When you look at boxers, the body weight they compete at is quite low, in relation to their height. There are exceptions like Mike Tyson (around 96–100kg at 179cm) or David Tua (110kg at 178cm) but otherwise boxers are quite lanky. Think someone like Carl Froch who at the height of 186cm competed at super middle (76kg).

Bodybuilders on the other hands train to achieve as high lean body mass as possible. They’re not bothered by the fact that that muscle is not practical in the fight scenario. They just want to look good. When you train with this goal in mind, the product of their training (sarcoplasmic ‘bodybuilder’s’ muscle) will actually become a burden in a fight/sparring scenario where you need to be able to both pack a powerful blow (and actually often hundreds of them) and move all the time to avoid getting hit.

I think you could potentially make up for all the energy burnt in the martial art training. You’ll just have to consume more calories which would theoretically keep calorie surplus needed for hypertrophy. I would however ask myself a question what’s more important because you can’t really excel at both.

Cardio has no effect on hypertrophy other than reducing body fat content, which will show muscle definition all the more. Further, full range motion exercises like kickboxing will emphasize flexibility and mobility.

Hypertrophy slows down naturally after 10 to 12 months of building, when one’s body starts to get used to the strain being put on the muscles. There is no solution for this other than perseverance and long, slow continuous building.

I would say no, I don’t know the science of it but look at guys like Klitschko, Tyson, Holyfield, and Joshua. They’ve boxed a lot and look pretty hypertrophic to me but I can’t say I know all the “supplements” they are on. The only thing I could think of to help ease the conflict is to really work on flexibility to help keep your big muscles able to move the way a kickboxing match requires.

No cardio won’t, however when focusing on intense cardio, you must focus on your protein intake (diet).