Knee push ups, are perfect if you can't do a single normal push up. These are also great for a warmup. I actually used to do a lot of these back in my Judo training days. We used to do at least 100 every time. Enjoy!

To perform a pushup, lie down in prone position. Place the palms of your hands on the surface at shoulder width and straighten your arms at the elbows. Place your kneed on the floor and bend them at 90 degrees. The rest of your body should be perfectly straight. Only the palms of your hands and your knees should be touching the surface. To begin the exercise, start bending your arms at the elbows and lowering your body down until your chest touches the surface. Now from this position, push with your hands and start straightening your arms at elbows until you are back at the starting position. Remember to keep your whole body straight and to go as low as you can while performing the exercise. Also, try to do the exercise slowly and with control. Pushups train mainly your pectoral muscles (chest), triceps and anterior and lateral deltoid (front and middle part of the shoulders).