If you're looking for low-tech, efficient fitness moves that you can do just about anywhere, then the classic push-up should sit high up on your list. When done correctly, push-ups build strength in the arms, chest, shoulders, abs, and lower back, all in one simple exercise! But form is important, so while you may be able to do 50 sloppy push-ups, you may find doing 20 excellent push-ups more difficult. Read more about this perfect, no equipment exercise here, or watch this video of Ford model Chris Comfort to learn how to get more out of your push-up.