He is such a gym rat, he spends hours there every day.
Он такой человек, который постоянно занимается в спортзале, он проводит там часы каждый день.
Definitions
A 'gym rat' is a colloquial term used to describe a person who spends a significant amount of time at the gym, often engaging in weightlifting or fitness activities, and is highly dedicated to their physical fitness and bodybuilding goals.