You're Sitting On A Time Bomb By Paul Scott
Copyright Mens Health Magazine April 2008
Your office chair -- the foul line for every Nerf free throw and your box seat on the working world -- has you fooled. You think it makes you powerful when it really makes you weak. You think it rests the machinery of your back when it's silently causing your back to compress, crush, and fail. You think its adjustable armrests and hydraulic height control offer you choices, but the most important option of all -- the option to stand up and move -- is the critical way your chair undermines you.
We live in a free country, but sitting is mandatory. In the late 1980s, office workers spent 70 percent of their days seated. Today's desk jockeys ride the unforgiving chair 93 percent of the time. Those who are paid to do clerical work may spend closer to the full 100 percent. That's just the sitting required to earn a living. Add to that the growing number of hours you spend seated while commuting, watching 24, tracking your NCAA pool results, or doing pretty much anything on, say, a Bowflex, and the remainder of your day is one long game of musical chairs. Life treats you like the waiting room at the DMV. Take a number, be seated, and wait your turn for the big back attack.
But at least seated jobs are safer, right? After all, you can't crush a finger in the machinery of investment banking. Well, if desk duty lowers your risk of on-the-job amputation, it's now clear that sitting for a living will slowly but surely increase your risk of developing back problems. Occupational sitting can damage your back in a variety of ways, but the real demon unleashed by sitting comes from the mundane fact that your back is pulled out of its natural position when you place your legs at a 90-degree angle to your hips. Studies show that when you drop into a chair, your hips stop rotating after the first 60 degrees of descent. To move your legs the final 30 degrees into position, "the muscles of the back of your thighs pull the bottom of your pelvis forward to tip it backward," says Galen Cranz, Ph.D., a professor of architecture at the University of California at Berkeley and the author of The Chair, a withering criticism of our most ubiquitous piece of furniture.
"That," says Cranz, "flattens the lumbar curve." (If this were a horror movie, lightning would strike right now.)
For decades, researchers have argued that flattening the lumbar curve--the concave segment of the spine also known as the small of the back--leads to pain. But until Stuart McGill, Ph.D., first fired up his ominous-looking disk-herniation machine, no one had wrecked an actual spine to prove the point.
For 25 years, McGill, the director of the spine biomechanics lab and chairman of the department of kinesiology at the University of Waterloo, in Ontario, has rewritten the book on back-pain prevention. Where others have made guesses about how the back works, why it goes bad, and which exercises can help ward off pain, McGill has taken the measurements and run the experiments. He has produced some surprising results. By merging evidence-based medicine with real-world observations of everyone from office drones to pro athletes, McGill has debunked more than a few back-safety myths, starting with the popular advice to "lift with your legs, not your back." (It turns out you should lift with your hips, not your legs.) He has also cast doubt on the common misconception that drawing in your belly button when you exercise stabilizes your core. In McGill's view, you're far better off bracing your abdomen, much as you would if you were about to take a punch in the breadbasket.
Hoping to pry some of this secret knowledge away from the physiology-seminar circuit, I met McGill, an imposing former college football player with a walrus mustache and a handshake that could crush granite. I had a dual motive, the first part of which was to enlighten you, the chair-threatened reader. But I'm also the owner of a lumbar spine that first seized up on me after a rim-leaping drill on a basketball court at the age of 28, and it troubles me anew every time I take to the chair for multiday, 12-hour stretches to write articles like this one. I wanted, needed, to learn from the best.
Go on to the next page for more on the hazards of occupational sitting...
McGill's lab includes rooms for the study of spine biology, and computers loaded with software he designed to compute the forces placed on the spine during different exercises. There are infrared cameras to analyze spines under load, and rooms full of handmade plywood gizmos designed to explore the human backbone in action.
But the real wet work of McGill's quest -- the crushing, twisting, and flexing of actual spinal flesh and bones -- happens in a 12-by-12-foot chamber crowded with an x-ray machine, a workbench, and three specially designed materials-testing machines dedicated to wrecking newly harvested pig spines (courtesy of the local butcher). Essentially a set of high-end paint-can shakers, McGill's disk-herniation devices lock down connecting segments of a pig spine and then rattle them enough in a matter of hours to simulate a lifetime's worth of flexing, rotating, and compressing.
"The machines flex, bend, twist, shear, and compress," McGill says of the devices. "They show us exactly what too much sitting can do."
On the occasion of my visit, a Ph.D. student, Janessa Drake, was busy using aluminum and wires to prepare a pig's spinal segment for analysis in one of the bone-rattling protocols. It's not squeamishness that led McGill to use pig spines instead of human ones. Donor human backbones are generally too weathered from use to reveal much about the way healthy spines respond to repeated flexion, he says. And besides, "a pig neck, believe it or not, is really close in size to the human lumbar vertebrae, and it gets injured in the same way."
Fresh from the butcher, a 3-foot-long section of bagged and taped porcine vertebrae sits on the floor at my feet. "It's pretty close in size to yours," McGill says, eyeing me.
As it happens, these pigs gave their lives for something more than just breakfast at the local diner. McGill has learned that for those of us who are susceptible, simply flexing the lower back while sitting in a chair -- with no load whatsoever -- will wreck the disks as surely as entering a strongman contest while drunk will. Thanks to McGill's disk-herniation machine, we now know that as few as 6,000 bends of the spine under the weight of your upper body is all it takes to cause the gel at the center of your disks to herniate or even rupture their outer casings.
The degree of damage caused by repeated spinal flexion varies, and the damage can be offset by rest and exercise. Pain arises when disk gel finally herniates (by bulging like an inner tube out of a tire) or ruptures altogether. In both cases, disk matter comes into contact with nerves. Either way, McGill puts one issue to rest: Nothing wrecks the back like a chair. "We tried many ways to induce disk herniation," he says. "The easiest way was through repeated flexion."
If all he did was wreck disks, you might write McGill off as a Dr. Frankenstein of the spine--a brilliant man who needs to come out of his dungeon once in a while. But McGill has more experience with the human back than perhaps any other scientist in his field. He is sought out to evaluate back cases by the NBA, NFL, NHL, PGA, Major League Baseball, world-class powerlifters, and athletes from nearly every Olympic sport.
These elite athletes return from their pilgrimages to McGill's lab and research clinic armed with some of the same basic back advice he offers to healthy young people whose only liability is too much time spent in chairs: The spine is at its strongest in its neutral position, the S-shaped alignment of your 33 vertebral bones with interconnecting disks. Save your S, and you'll use the lumbar curve to balance the weight of your head over your center of gravity and keep your spine out of the red zone. If you sit for a living, he says, there is no better use of your workout time than to begin training your back smarter, and to do so while it is still healthy. "It's hard to motivate the uninjured," McGill says. "Once they're injured, I have their attention."
The four horsemen of the spinal apocalypse
The conventional wisdom on back pain has proved woefully inadequate. For decades, we've heard that back troubles spring from two factors -- weak abdominal muscles and tight hamstrings. This version of back pathology generates the same rudimentary advice: Strengthen your abs with situps, and stretch your hamstrings with leg stretches. McGill insists that some of this advice is too general, some is flat-out wrong, and some can actually increase your risk of back injury. The reason some backs go bad is neither tight hamstrings nor weak abdominals, he says, but because of problems with the activation patterns of those muscles. So he's more concerned about the four types of loads on the back -- flexion, shear, compression, and twisting. Counteracting them is like taking out a major insurance policy on back health.
When it comes to your back, too much flexibility is bad. Flexing your lumbar curve with every descent into a chair may hasten the destruction of your vertebral disks, and it creates an additional danger by causing your spinal ligaments to become dangerously lax. People with back pain have less stable spines than those who are healthy, and that probably puts their disks at risk, too. The importance of having a tight spine -- that is, a spine well supported by muscles and ligaments -- has made McGill not only wary of excessive stretching but also more inclined to warn athletes of the risk of sitting for a lengthy period and then springing up to do something arduous. "Your spinal ligaments can stay lax for an additional 20 minutes after you stand up," says McGill. You know all those NBA guys with balky backs? Think about the toll placed on benchwarmers required to sit "with their knees in their ears" and then told to go box out Dwight Howard.
Shear forces are incredibly destructive to your back. When you bend from your lumbar curve (flattening the S) and then compound the mistake by picking up something heavy, shearing forces are generated by the back-to-front sliding pressure placed on your disks. It may sound like a boneheaded thing to do, but during any given day we find a way to impose shear on our spines every 15 minutes or so. Lean forward from your chair to stand up, for example, and you subject your vertebrae to shear. However, if you pull your shoulders back and chest up, and hinge forward at the hips to rise straight up from your chair, your back will be safely locked in its neutral position. If you're thinking that this instruction is about good posture simply for good posture's sake, consider the specific anatomical rationale for moving with your back locked in neutral. When you do this, you protect your back from shear, thanks to the orientation of the fibers of two vertical lumbar muscles known as the longissimus and the iliocostalis. Allow your lower back to become flattened or rounded, however, and the fibers of those two muscles turn almost parallel to your spine, which virtually eliminates their ability to offset shear.
Bending and lifting both compress your spine on an incre-mental basis, but one-time mishaps, such as squatting with too much weight, slipping and landing on your rear, or hitting a hard spot while riding a toboggan, can also pile-drive your disks. Traumatic compression injury begins with the silent disaster of a vertebral plate cracking, which sets into motion the gradual flattening of your disks, a process that eventually leads to pain. But even if you've religiously avoided bashing your tailbone, you could still be in trouble. People who sit for most of the day are asking for it, because a desk chair imposes a low-grade but long-term compressive load. "If you sit in a slouch," says McGill, "your ligaments compress the spine. If you sit upright, your muscles start compressing the spine."
Your only solution is to use a chair with good lumbar support and to make sure the lumbar-support cushion is nestled into your S curve. Also, raise the seat, com-puter screen, keyboard, and desk surface closer to barstool height. This puts your hips in the 120-to-135-degree range and helps your spine remain in neutral. And take breaks from sitting: Stand up to answer the phone, and visit -- don't e-mail -- a colleague.
Rotating your upper body without simultaneously rotating your pelvis will, over time, slowly squeeze the gel from your disks and damage their outer layers. If you're seated as you read this and you need clarification, take note: "When you're at your desk and you keep twisting to reach your phone, every twist while flexing creates a combined load, which doubles the destructive effect," McGill says.
Of course, rotational exercises -- cable woodchoppers, twisting medicine-ball throws, and oblique crunches, for example -- have become commonplace in the past few years. Are they spine wreckers? It is possible to rotate without increasing your risk of spinal load, says McGill, if you move your upper and lower body as a single unit. To preserve the neutral spine position while doing rotational exercises, imagine that you've nailed boards from the bottom of your rib cage to the top of your hips so your pelvis and rib cage move as a block. Ignore this advice at your own risk. "Twisting torque," McGill cautions, "creates four to five times the load on the disks compared with other kinds of movements."
So now that you've met the four horsemen, what will you do? It's quite simple. Respect your spinal S curve. Don't flatten it or overload it, and surround and fortify it with muscle. And back pain will be one more grumpy-old-man ailment you'll never have to complain about.