Stand with your feet together and your arms out in front of your chest for stability. Take a large step back with your right foot.
Lower your hips until your left thigh (front leg) is parallel to the floor, with your left knee positioned directly over your ankle. Your right knee should be at a 90-degree angle, pointing toward the floor with the heel lifted.
Drive your right knee up toward your hands, maintaining that 90-degree angle.
Immediately go back into a lunge, and repeat with the same leg for the full 40 seconds.
Once the 40 seconds is up, rest and complete the move with the left leg.