Do It: Grab a pair of five-to 10-pound dumbbells, stand in front of a bench or step, and place your left foot firmly on the step. Press down with your left heel and push your body up until your left leg is straight. Slowly lower back to the starting position. That’s one rep. Do all reps with the left leg, then repeat with the right.
The reason this was the inspiration behind an exercise-class empire? It works.