Why is sitting in a chair for long periods bad for your back?

There are four curves along the length of our spines that form an "s" shape. People with good posture maintain that natural figure, which is optimum for the back. But if you're on a long car trip or sit behind a desk all day, perfect posture can be difficult to keep up. You twist around in your seat, sprawl out with a book or hunch over a computer. After a while of not moving, your back is beat.

People with desk jobs may spend more time sitting in their office chairs every day than lying in their beds at night. For at least eight hours each day, many employees remain firmly planted in their chairs. Spending so much time in the same chair, you get to know its contours and nuances as you shift and slouch your way through the workday. You might not notice that the chair is taxing your back until you're popping a handful of aspirin to alleviate the painful crick in your spine.

The field of ergonomics examines how the work we do affects our bodies. It focuses a lot on the elements of force and motion. When sitting, the force of your upper body settles into your lower back, in the lumbar region of the spine. That's why you often hear about the importance of proper lumbar support. On top of that, if you have to move around often in your seat, it can increase the back's workload even more. Instead, when sitting, you want the chair to promote a neutral body position that keeps your vertebrae aligned. This reduces your chances of developing musculoskeletal disorders in your back.

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The most important thing to remember to avoid chair-related back problems is that your chair sh­ares the burden of supporting your body weight with your back. The more of that load you give the chair, the less work your back has to do. In a way, you should think of chairs as having a specific fit. Goldilocks was onto something when she tried out all of the three bears' chairs until she found the perfect one. Like a pair of shoes that are too small for your feet will rub and cause blisters, a chair that isn't adjusted your body will promote back problems. To know whether a chair fits, here are a few rules to sit by:

­But don't let yourself get too comfortable for too long. Holding your body in a static position for a sustained period will always stress the muscles involved at some point. Doing that day after day invites permanent physical problems. The key to reducing back pain from sitting for a long time is motion. Every 20 minutes or so, stand up, stretch and walk around if possible.­

When you aren't confined to a chair, stand up and stay active. By exercising, you strengthen those muscles surrounding your spine. Maintaining a healthy weight will also lighten the load that your lower back must bear. With a healthier body overall, you'll feel better and sit a little taller.