Because Crossfit contains a lot of cardio and high intensity training many people fear their muscles will fatigue and they will end up being catabolic and loose their muscles.
They have been training hard in the gym and they have done their biceps curl year in and year out, and of course don’t want to jeopardise destroying this hard work with crossfit?
True, traditional bodybuilding and high-intensity cardiovascular training do not always mix. If the goal is to look like a bodybuilder, crossfit obviously is not the type of training you should choose.
But Crossfit consists (amongst other exercises) of heavy Olympic lifting, gymnastics and classical bodyweight exercises such as pullups, dips and pushups. Therfore it’s impossible that crossfit training would magically transform a muscular body into a stick. Just the same way it will not make you to look like Mr Olympia.
Let’s say you are a beginner starting to train Crossfit. Of course you will get an increased muscle mass of doing above mentioned exercises. The body will respond to all muscle building exercises, no matter what you’re doing.
Well, you become what you train. However, the argument that crossfit will make you become small and completely free of muscle is not correct.