Instructions:

1. Start in a push-up position with your hands shoulder-width apart and your body in a straight line.
2. Lower your chest towards the ground by bending your elbows, keeping your body straight.
3. Push through your hands to extend your arms and return to the starting position.
4. Quickly bring one knee towards your chest, then quickly switch and bring the other knee towards your chest.
5. Continue alternating knees as fast as you can while maintaining good form.
6. Continue for the desired duration or number of repetitions.