It depends on the bodybuilder and what kind of bike they're on. If they're cycling for fun, they might cruise around 20-25 km/h, but when it comes to sprinting, some could easily hit 40 km/h or even more.

I was heavy into the gym before they closed them during covid and I started cycling instead. I was amazed at how slow and rubbish I was on a bike despite having a fairly sturdy squat and deadlift. But the first time I did a sprint (was on zwift so very little skill needed) I decimated all lol. 3 years of cycling and several mutli-day tours later I’ve gone from rubbish to mediocre. I’ve still got a good sprint though. It really is a different type of fitness. BTW this is all on non-e-bikes. I used e-bikes to get my fitness up initially though.