If you missed it, read the down-low on what Greatist's Renew Year Challenge is all about.

Renew Year 21

Stale workouts suck. But know what doesn’t? Interval training. (Not to mention, it can slash your workout time in half!). So turn up the speed, get sprinting, or tango with Tabata. You can even steal our CEO’s favorite workout.

Wipe off the sweat, recover with some protein, and tell the universe how fit you feel.