a gym junkie
a TV junkie
A: Wow, Martin, you looks so buff.
B: Thanks, Dennis. I've been hitting the gym every day for about six months now——an hour of aerobics in the morning and then I pump iron and swim after work.
A: I can't believe that you've turned into a gym junkie. Are you sure that you're not overdoing it?
B: Not a chance. You remember how I was before. I was so overweight that I had no energy and lacked the confidence to approach girls to ask them for a date. Now I feel like I'm Mr. Universe.
A: Well, good for you. Here's my telephone number. Call me for a date sometime.
B: No can do, Denise. I'm too busy hitting the gym.