You don’t need a gym membership to get a total body workout. In fact, you don’t even need equipment. Exercising using just your body is completely free and can be just as effective, if not more so, as spending hours a day at the gym.

Let’s take a look at some of their best ideas from the “Core/Midsection” section of Lifehacker’s extensive fitness article. Simple sit ups just don’t cut it. By practicing many variations of the sit up, you can target your entire core and get a more effective workout. Take a look:

The Roll Up

The (Half) Roll Down

The Hundred

These are just some of the exercises recommended by Lifehacker. Find many more over at How to Get a Complete Workout with Nothing But Your Body.