"hitting the gym" is correct and usable in written English. You can use it when referring to working out or exercising at the gym. Example: I'm determined to reach my fitness goals, so I'm hitting the gym five days a week.
According to research published last month, walking is better for you than hitting the gym.
There's no way you can maintain that muscle without hitting the gym 100% full on.
So dogs have been hitting the gym for fitness programs at kennels and pet spas around the country.
Frustrated by the tight job market, Mr. Badhorn works off his stress by hitting the gym every day.
He had been hitting the gym -- he could squat 500 pounds -- but then he began to focus solely on riding.
With the start of a new year, many people resolve to shed their holiday paunch by hitting the gym more frequently.
Too late to hit the gym?
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.