PHOTOGRAPH BY BETH BISCHOFF

Most people use 21s with biceps curls. The classic bodybuilding technique—which involves doing the exercise using various ranges-of-motion—stimulates new muscle growth.

But why should your biceps get all the love? Use 21s with Bulgarian split squats to give your legs an incredible workout.

Here’s how to do it: Perform the following rep scheme on one leg without stopping.

1. 7 bottom-half reps
2. 7 top-half reps
3. 7 full reps

Once you hit 21 reps, perform the couch stretch for your quads and hip flexors on the same side you just worked. Then switch legs and begin again. That’s 1 round. Do 2 to 4 rounds per side.

Master this routine with just your body weight first, and then increase the load using a weight vest or dumbbells.