gym junkie

Translations
человек, помешанный на тренировках
He's become a real gym junkie since he joined the new fitness club.
Он стал настоящим человеком, помешанным на тренировках, с тех пор как вступил в новый фитнес-клуб.
Definitions
A person who is extremely enthusiastic about going to the gym and working out, often making exercise a central part of their lifestyle.