Little research has been done on the best way to sit upright. One American meta study in 1999 concluded that sitting at an angle of 110 to 130 degrees was optimal for spine comfort. A Scottish study published in 2007 found that leaning back at 135 degrees is ideal to prevent back strain. While interesting, this sort of precision may be impractical for most people, Dr. Golubic says.

His clinic sees patients with multiple chronic illnesses. Nearly all of them sit for long periods each day. The term Sedentary Death Syndrome was coined by the President's Council on Physical Fitness and Sports in 2002 to address the growing consequences of a seated lifestyle. 'There are studies on Sedentary Death Syndrome that show that sitting for hours can cause anything from lower back pain to high cholesterol, diabetes and obesity,' he says. In other words, no matter what position you're sitting in all day, it is pretty bad for you.

Body posture determines the efficiency of your breathing. 'Relaxed, straight sitting' -- with the core strong, shoulder blades active but not tight and spine erect -- 'expands your chest, allowing you to take in a larger breath . . . and you'll have more energy and focus,' Dr. Golubic says. To achieve this, sit away from the back of your chair so you don't slump, with your feet placed firmly on the ground. He sometimes sends patients home with a blue dot to put on their computer screens as a reminder to sit up straight and stretch and take a deep breath when they feel pain. There is also an app called PostureTrack that alerts users when they're slumping.

It's not as though slouching will give you a hunchback in a day, but 'if you do this day after day, and your muscles are not strong, the whole skeleton changes,' Dr. Golubic says. 'I'm not aware of any studies that look at the changes in the volume of organs like the liver and spleen when you sit straight or slump forward. But we do know that when you slouch, you project an attitude of depression and low motivation.' When you sit up straight, he adds, 'psychologically, your attitude is better.'

If you're not used to sitting up straight, you may feel lower back pain -- an indicator that you need to strengthen your core and work on general fitness. Dr. Golubic almost always advises his patients to start yoga: 'The first thing we learn in yoga is how to sit properly.'

The bottom line: How you sit is less important than how long you sit, Dr. Golubic says. He tries to get up from his desk often, doing 'walking meetings' with colleagues and taking phone calls outdoors. 'If you cannot walk,' he says, 'At least stand.' Subscribe to WSJ: http://online.wsj.com?mod=djnwires