9: Strengthen Your Core

Crunches are a classic core exercise, with many different variations.

There's a lot of talk in the fitness world about strengthening your core. This group of muscles consists of the center, or core, of your body -- the muscles in your middle and lower back, abdomen and pelvis. These muscles are important in just about any movement and, when it comes to sexual positions, they contribute to the thrust, so to speak.

There are lots of different exercises that you can do to strengthen your core. Crunches are a classic core exercise with which you're probably already familiar, but another great maneuver you may not have performed is known as the quadruped. Start out on your hands and knees, with your hands aligned under your shoulders and your knees aligned with your hips. It's important to tighten your abdomen and remember to breathe.

Then, lift and straighten your left arm and right leg so that they are level with your spine. You'll really work your abs and trunk muscles while trying to maintain balance. Hold for a few seconds, release, and then alternate using your right arm and left leg. If this is too difficult, try just lifting an arm, then a leg, then an arm, then a leg. Slowly work up to holding this exercise longer and doing more repetitions.