If you ask 10 people what the ideal sitting posture is, most if not all will reflexively offer some variation of “sit up straight.” It’s an answer assumed to be so obvious there’d probably be some suspicion as to whether it was a trick question. Well, it’s not a trick question. But neither is the answer obvious.
The textbook definition of proper sitting posture is sitting in an ergonomically correct chair with your back upright, your hips and knees bent 90 degrees, and your feet on the floor. Of course, that was before Stuart McGill’s textbook (Low Back Disorders, Human Kinetics, 2007). Dr. McGill, a prominent researcher in the field of biomechanics, notes that the above description may in fact be the “ideal” sitting posture…but not for more than 10 minutes. His point is that sitting puts significant pressure on the back (particularly the spinal discs, but also the muscles, connective tissue, etc. depending on the specific position) and that that pressure is detrimental to any tissue subjected to it for prolonged periods. The real goal then should be to prevent any given structure or tissue from bearing the brunt of sitting for too long, something that can be accomplished by regularly shifting position. Or as Dr. McGill sums it up, “the ideal sitting posture is a variable one.”
He therefore recommends frequent (several times per hour) changes in sitting position: leaning the seat back while keeping feet flat on the floor, sitting back and propping your legs up on the desk, even crossing your legs “Indian style” in the chair. While there are benefits to sitting in an ergonomically correct chair, staying in any position–even a technically correct position–for a prolonged period of time is just ill-advised. According to Dr. McGill, the most effective way to take advantage of an ergonomic chair is to periodically adjust the different parts so that your joints aren’t always at the same angle. In general, the seat pan should be positioned such that your knees are level with or lower than your hips when sitting upright. This will promote some extension of the low back and will relieve seat-edge pressure behind the knee. And sitting upright should be nearly effortless. If you’re sitting so rigidly upright that it’s effortful, you’ll be in an unnatural position that will increase the pressure on and fatigue your back.
Finally, don’t forget to take some relief from sitting altogether. Roughly once per hour, it is very helpful to stand up, gently stretch your arms towards the ceiling, and take a deep breath.
TIP: The proper sitting posture is one that is constantly changing.