The F1 guys are probably as fit as a top footballer. They're dealing with black out levels of lateral G forces whilst slamming on the brakes within a fraction of a second of loser times or crashing out.
The MotoGP guys are far more fit - they have to use their bodies as counter ballast to make the curves. That's why MotoGP races are so short, they're at the limit of human endurance.
Look up any of these guys' gym routines