Inspired by Todd Hargrove’s post at BetterMovement.org: “Is “Efficient” Movement Unsafe?”
The Back Extensor Group of Muscles
I remember reading that good posture was the most energy efficient way to stand and sit. But why does it seem to take so much more energy to keep the spine straight than to slouch, especially with fatigue or illness. If energy efficient means using the least amount of energy to perform work then at first glance, slumping with rounded back does seem to take less energy because the back extensors, a large group of back muscles, slack off from straightening the back and let the weight of the upper body hang passively off spinal ligaments and joints. But is the spine well suited to supporting this much dead weight by itself? The short answer is “NO” because the spine has inherent flexibility that allows it to bend when needed for everyday activities. The fact is that by itself the normal spine cannot be both flexible to allow us to bend down to tie our shoelaces and inflexible enough to completely support our bodies. A fused spine can’t bend and therefore doesn’t need stabilization, but a normal, flexible spine does need the stabilization that is provided by the balanced action of two antagonistic groups of muscles—the back extensors, which bend the spine backwards (and keep us erect), and the front abdominals which bend the spine forward. For ideal posture the extensors and flexors act in concert to stiffen the spine in as close to a vertical position as the natural curves allow. This is the spine’s most stable and least stressful/damaging upright position and results in even distribution of compressive forces on intervertebral discs.
When the back is excessively rounded forward, discs are unevenly stressed, and over time their outer layer or annulus prematurely develops tiny cracks that cause loss of moisture and disc height, which causes spinal instability, increased pressure on facet joints, bone spur formation and stenosis. A rounded back also causes an imbalance of head and upper body weight. Optimal distribution of body weight is important for our ability to stand upright. Moving around on two legs is precarious to begin with. And if the ten to fourteen pound head juts out in front of the body because the top of the thoracic spine curves forward, and the upper chest and back, shoulder and arms also curve forward, it’s more difficult.
There is already a natural imbalance of weight due to the rib cage chest area extending out front of the thoracic spine,
(which has a natural kephotic (posterior) curve to counterbalance the rib cage (see balanced posture at left) and this weight imbalance causes a constant forward bending pressure on the spine that must be resisted for the body to stay upright.
With excessive rounding of the upper back, the body must realign itself to keep from falling forward. One of three strategies is used:
1. The pelvis rotates backwards, trying to pull the upper body upright, and pulls both the lumbar and mid thoracic spine flat. But since the upper back and head are still held forward of the torso, and there’s no counter-balancing curving of weight to the back, the entire body leans a little forward, not so much that one would fall over (unless trying balance exercises), but enough to have difficulty flattening the entire back and head against a wall without extending (bending slightly backwards) the back. see Flat Back Posture
2. The upper torso shifts backwards in a long, rounded curve that is also counterbalanced by the pelvis shifting forwards. See Sway Back Posture.
3. The excessively hunched upper back is counterbalanced by the abdomen, which pooches out in front because of an excessive inward lordotic curve of the lower back. Against a wall, the upper back and butt may touch, but there’d be lots of space between wall and lower back. See Kephotic-Lordotic Posture.
All three strategies/postures produce their share of sore backs and necks.
Now, getting back to the subject of “Efficient Movement.” A better definition for “efficiency” would be “The least energy used to achieve the best possible result.” The back extensors must be engaged to stabilize the spine, so that body weight and other forces are borne with vertebra stacked vertically, one on top of the other and the forces are spread evenly on discs and ligaments. When the back is as straight as possible, given the natural curves, body weight is close to being balanced around the spine. The vertical black line (the center of gravity) in the posture illustrations, represents equivalence of weight in front of and behind the line. When weight is balanced, posterior muscles like back neck muscles and lower back muscles, as well as hip extensors (hamstrings) (depending on the type of faulty posture) are not over-worked. But also front postural muscles like neck flexors, abdominals and hip flexors are not under-worked and weak.
In Todd Hargrove’s words: “any local gains in energy efficiency from “floppy joints” are more than offset by a general loss of energy efficiency that comes from poor alignment of the bones and inadequate stabilization of the joints….In other words, valgus knees (knees collapse inward), rounded backs, and overpronated feet (foot rolls inward and arch collapses) are not actually energy efficient at all, because they sacrifice the stabilization and proper bony alignment which is the key to efficient movement and posture.” Yes, it feels easier to slouch especially when one is tired or not feeling well. Add a chronic illness, and it seems like there’s little energy left to stand tall with good posture. But it is so worth the effort because the strength and balance of postural muscles is preserved and the chances of postural neck and back pain are greatly reduced.