Push-ups build core, chest, back and arm muscles. A chair presents a way to modify push-ups while gaining the same benefits. Set the seat either facing or away from a wall or other sturdy structure. This will keep your chair from sliding during your push-ups. Place your palms on the seat or back of your chair. Walk your legs back into a plank position. Engaging your abs, bend at the elbows and lower yourself down. Then push up through your palms to return to the starting position. Do 10 – 15 reps.