When you think of a hedgehog, you might imagine them using their unique defense mechanism: curling into a tight, spiky ball.

Although controversial, sit-ups can be an effective exercise if done properly, what I call "good" sit-ups. Lie on your back, knees slightly bent with heels on the floor.

Sit-ups are a simple bodyweight exercise. Here's how to perform sit-ups safely, according to experts, and the muscles worked, along with the benefits.