This article originally appeared on Martin Memorial Housecall, a blog published twice a week providing information that can help you navigate health care, prevent disease and live longer. To visit the blog, go to www.martinmemorialhousecall.blogspot.com.

If you have heard any advice when it comes to exercise, this line may sound familiar: "You have to strengthen your core."

The American College of Sports Medicine (ACSM), defines the core as the trunk or link between the upper and lower extremities. The trunk is made up of the spine, the pelvic girdle, and the rib cage.

Many of the exercises that we teach at the Martin Memorial Health and Fitness Centers originated from rehabilitation. Many of these core exercises were intended for treatment of low back pain and injury.

"Pull in your belly button!" Fitness trainers are constantly reminding people to do this while exercising and throughout the day to support the lower back. If you keep your core drawn in (your belly button tucked), it will put your body in proper alignment.

Some of the best core exercises are known as planks, bridges, and side bridges. These exercises can be very challenging. For example, a plank is a held or starting push-up position. Try holding that pose for 30 seconds. Do you feel your abdominals and "glute" muscles tighten to keep your back from arching? That's a core exercise! This type of training is a sure-fire way to "fire up" your abdominals much more than the traditional "crunch."

Once you conquer the plank for 60 seconds, try placing your hands on a stability ball. There are many options to continually challenge the core. BOSU balance training, stability balls, pilates and yoga all focus on core training.

Here's something to think about. I was just cutting up a pineapple from my neighbor's garden and we had a "light bulb" moment. The pineapple core is the strongest part of the fruit. Now it makes sense that our own bodies need to be their strongest at the core.

But here is something else to think about: Do not eat the core of the pineapple. It's really "hard core."

--Jane Reynolds

Health and Fitness Technician, Group Exercise Instructor

Martin Memorial Hospital South Health and Fitness Center