Identical to the set up for a push up. Place the hands flat on the floor and directly below the armpits. Back is flat and elbows are extended.
While keeping the weight over the hands, begin to bring one knee close to the chest. Lightly tap the toe and kick the leg back, alternate the legs rapidly.
During the set the hands stay directly below the armpits and the back remains flat. The legs are the only part of the body moving.