While standing in an upright posture, step forward with your right leg so that your right knee makes a 90-degree angle between your calf and your hamstring. Your left knee should hover just above the ground. Explode upward, alternating your legs in the air so that you land with your left leg forward. "I jump up, flip [my legs] in the air, and land, then jump up, flip [my legs] in the air and land, back and forth," says Bas. Thirty repetitions should have you close to tears.