During 25 years of training, I’ve seen push-ups used in high school gym classes, the military, and dojos, often as a form of punishment. With good reason: Push-ups are tough. While people at gyms spend lots of time on benches and other fancy equipment, push-ups may be an even more effective way to get you stronger, faster. And they’re far more versatile than people think. Push-up variations can strengthen your abs, back, legs -- pretty much every muscle in your body, really. Here are 10 versions of the push-up you aren’t doing but should be, divided into four categories. Add them to your workout and you’ll see (and feel) powerful results.