Yesterday Marcy suggested we hit the beach this weekend, which immediately made me lift my shirt and check out my abs. A not uncommon reaction, I’m guessing.

When we think of exposing our bodies to the world at large, we tend not to think of our chicken-wing shoulders, our flabby arms, our spindly legs: Our gut reaction is to think of our gut. While obsessing over six-pack abs and a flat tummy may seem the ultimate in physical vanity, it’s actually a primal response grounded in sound physiology. As any trainer will tell you, the key to physical well-being starts with your core muscle group.  Build strong back and abdominal muscles and you’re building the foundation for overall physical health. If it makes you look hot in the process, so much the better.

Now, I do core exercises at least five days a week. But while I’ve been good about adhering to this truism of fitness, I’ve been bad when it comes to a another: Mix it up your exercise routine. With minor variations, I’ve been doing the same ab exercises for as long as I can recall. The problem with repetition? Your body gets used to doing the same exercises over and over, it becomes increasingly efficient at doing those exercises and your return on investment diminishes. Considering the variety of effective abs exercises out there, doing the same three or four over and over is plain silly. So this morning, instead of getting up and lemming into my usual routine, I logged on and Googled “free ab exercises” — “free,” because there are a plethora of machines on the market that work the abs, machines that may help, but aren’t necessary.

After sifting through several sites, I settled on the recommendations from the American Council on Exercise,  based on a 2001 study. That study evaluated 13 exercises, six of which involved equipment. I eliminated those and wrote down the seven that didn’t:

• Bicycle Exercise
• Exercise Ball Crunch
• Vertical Leg Crunch
• Long Arm Crunch
• Reverse Crunch
• Full Vertical Crunch
• Plank on Elbows and Toes

I found descriptions of how to properly do each of the seven recommended exercises at About.com and made copies of each; Every weekday morning for the next month, I’ll randomly pick three to do that morning. After a month, I’ll visit ACE’s excellent Exercise Library and add three more workouts to the mix. The library is a gold mine for the do-it-yourself fitness buff, breaking down exercises by muscle group and providing graphic depictions of how to properly do each. Under “Ab Exercises,” the libary lists 55 exercises, 18 of which don’t require equipment. By the end of summer I plan to have 20 ab exercises in the mix, 20 exercises randomly tapped to keep my midsection surprised.

And, hopefully, smaller.

Homer could easily drop that Crusty innertube around his midsection with a mix of ab exercises every morning. That and cutting back on the donuts.