So as you might know already, to earn Gym Rat badge you need to earn 3 star rating on 50 gym workouts.
Which means you can earn it in 10 weeks earliest. 5 different workouts, then you earn the physical bonus for a week and you can't work out anymore.
Except... Gatorade reflex drill. It's repeatable and counts. I screwed up my sprint drill (rip my weekly bonus) so I was at 4/50. Now I'm at 8/50, gaining 4 drills by running the gatorade drill.
It still will take time - but considerably less than waiting 10 or more weeks.
EDIT: Finished it, got the badge. Took a while, sometimes had to wait for one person.