What do soccer player Mia Hamm, swimmer Michael Phelps, and NFL quarterbacks have in common? Toned glutes!

And if you think that's not something to comment on, take a seat and listen up. According to physical therapist Chris Kolba, Ph.D., at Ohio State University Wexner Medical Center, millions of North Americans who sit all day at work or are generally sedentary have developed “Dormant Butt Syndrome.”

Those flaccid backsides aren't just making your pants look baggy, they contribute to a roster of back, hip and knee problems.

Your butt muscles support your pelvis, hips and torso, and act as a shock absorber when you walk. But if they're dormant, you end up with tight hip flexors, lower-back pain and even knee problems that can lead to a meniscus injury.

So get up off that backside! More than half of you sit for almost eight hours a day. And sitting six or more hours a day elevates your risk of dying from cancer and other major diseases.

But changing your habits so you sit for less than three hours a day tacks two extra years onto your lifespan.

Stand up every 30 to 60 minutes. Walk the stairs in your office building, speed walk around the parking lot, do stretches at your desk.

At home, try stretch bands while watching TV. Get a pedometer and head for 10,000 steps daily.