The muscles which work the spine

As superbly designed as the spine is, it amounts to naught without the dynamic contribution of the muscles. In the way a puppet is a flummoxed pile of sticks on the floor without its working strings, the human spine and its segments are an inert, toppling pole without its muscles.

The muscles of the human body work just like the strings of a puppet. They pull on levers and make the body move. They allow us to keep the thinking, top part of the body up there and active so we can operate effectively in the outside world. Without the dynamic support of the muscles the spine would fall over. More than you would ever imagine, the muscles play a dynamically synchronised role in keeping the skeleton upright and controllable. You only have to see unfortunate cases of poliomyelitis to understand this point.

Figure 1.24 The rectus abdominus muscle runs up and down the front of the abdomen whereas the internal and external oblique muscles cross over each other diagonally making a wide 'X' and drawing in the sides of the waist.

external oblique internal oblique external oblique internal oblique

rectus abdominus cut edge of external oblique internal oblique

Figure 1.24 The rectus abdominus muscle runs up and down the front of the abdomen whereas the internal and external oblique muscles cross over each other diagonally making a wide 'X' and drawing in the sides of the waist.

rectus abdominus cut edge of external oblique internal oblique

With paralysis of the trunk muscles, the spine tumbles down around itself in slow motion, like a collapsing circular staircase, with the chest disappearing into the abdomen and into the pelvis. The tummy muscles play a critical role in keeping the towering spine up.

Tummy muscles also play a critical role in letting the spine bend. Although there is some confusion about the mechanism by which this happens, practising therapists the world over recognise the importance of a strong tummy in treating back problems. Still today, researchers cannot agree about the best way to strengthen these muscles. I certainly have my ideas which you will read about later in the book.

The abdominal muscles spread vertically, horizontally and diagonally, wrapping the soft abdomen in sheets of contractile tissue. As they contract, their fibres shorten and bow the spine forward. Working statically they nip in the waist, creating the 'hourglass' figure and flattening the belly. This effect reduces the intraabdominal space, which automatically raises the intra-abdominal pressure.

A strong tummy stabilises the spine from in front, in several ways. Firstly, a strong co-contraction with the back muscles lifts the spine vertically. This is similar to the upward movement of water in a plastic bottle if you grasp it around the waist. (If the bottle has no lid the contents spurt out the top.) The tension between the segments increases as the spine grows longer.

Secondly, a strong abdominal contraction pulls the belly in, slightly humping the low back and creating a contained pocket of high intra-abdominal pressure in front of the spine, like an air bag in a car. Apart from stiffening the spine, the back-pressure against the lumbar segments prevents them shearing forward on one another as the spine bends. As the bend of the low back becomes more accentuated and the tails of the vertebrae fan out like fish scales flaring, the posterior ligaments achieve their maximum tension and create a ligamentous lock. At the critical point, load is transferred from the muscles to the taut ligaments and the spine then becomes more stable.

As we bend, the abdominal muscles and their opposite number, the erector spinae muscles down the back of the spine, help in a

superficial long back muscles

Figure 1.25 You must always 'unfurl' to straighten with both the long erector spinae muscles and the smaller segmental intrinsic muscles working optimally around the hoop of the spine. The tummy must be pulled in hard.

superficial long back muscles deep back muscles

Figure 1.25 You must always 'unfurl' to straighten with both the long erector spinae muscles and the smaller segmental intrinsic muscles working optimally around the hoop of the spine. The tummy must be pulled in hard.

coordinated way to lower the spine over. From the front the tummy muscles provide the hydraulics for the fine precision. With fantastic, noiseless accuracy they allow us to adjust our height, while the long cables of erector spinae let the spine go, like a mechanical crane paying out. They particularly come into their own around the hoop of the spine when we are nearly at full bend.

Whether the bend is great or small, lowering the top-heavy column and then straightening it is a stupendously difficult task, especially when accompanied by lifting. Some mathematical calculations suggest the smallness of the long back muscles and the awkward angles make it impossible. Since we all know that our spines do bend and lift, and fairly effortlessly at that (though some better than others), we at least must concede the working spine is an awesomely effective thing.

With bending, the muscles of the spine and trunk work in two distinct ways: they centrally clench the segments together to keep them stable, and then they control the lowering over of the whole column. This vertical clenching of the spine is an important preparatory contribution to stability, while the bending itself is almost free fall. Rather than actually doing anything, the main job of the muscles is keeping control as the column goes over, so nothing comes undone.

Weakness in the central clamping-down action is one of the earliest things to go wrong with a back once it starts to break down. We do not know yet why this is so; whether it is a case of cause or effect. In other words, we cannot say whether the muscles reflexly inhibit once there is inflammation between segments, or whether the inflammation develops because there is weakness of the muscles keeping the segments together.

Coming up from the bend the whole process works in reverse. While the spine is still stooped, the ligamentous lock holds it stable and the unfurling starts by the pelvis rolling back. Then the static tensing of the abdomen thrusts us up from in front and the intrinsic muscles of the spine work at segmental level pulling each vertebra back. The long erector spinae muscles work around the hoop of the spine when we are in full bend, and then again like guy ropes once we are upright.

Figure 1.26 The deeper fibres of multifidus originate on the spinous process two vertebrae above and pass down and laterally to blend into the back of the facet capsules. Multifidus is the 'guardian' of facet opening and closing.

Multifidus Muscle

spinous process facet capsule

Figure 1.26 The deeper fibres of multifidus originate on the spinous process two vertebrae above and pass down and laterally to blend into the back of the facet capsules. Multifidus is the 'guardian' of facet opening and closing.

multifidus fibres spinous process facet capsule

Multifidus is—especially in the early part of range—the most important intrinsic spinal muscle. It originates either side of the spine, on the bony ring of the back compartment, right over the top of the facet joints. It is the deepest segmental muscle and its fibres actually blend in with the back of the facet capsules (which is significant with facet trouble, see Chapters 3 and 4). The fibres then pass upwards and inwards to their vertebra where they attach themselves to the spinous process. With the spine upright the line of pull of multifidus fibres is at 90 degrees (or right angles) to the spinous process it is attached to. Thus it is optimally placed to control the segments at the very first glimmer of bending.

In straightening from the bent-over position, multifidus initially gets a bit of help from the muscular ligament, the ligamentum flavum, each working its own side of the joint. The smaller front muscle tries to close the joint by sliding the two joint surfaces together, while the larger multifidus closes the gap by pulling on the tail at the back of the spine.

Multifidus's main role during straightening is to pull down on the tail of the tipped-forward vertebra, like pulling down an overhead garage door. As we straighten, the spine unfurls step by step in a segmental fashion, from the hooped-over position to fully upright. Multifidus is vitally important in controlling the stability of the spinal segments, and it works hand in glove with the important stabiliser of the front compartment, transversus abdominus.

Multifidus does another unique job as it helps the spine straighten. It hoists the facet capsules out of the way, rather like a damsel gathering up her petticoats as she goes to climb the stairs. This prevents the tender capsular lining being nipped as the opposing surfaces close down when the spine straightens. As you will read in Chapter 4, sometimes the muscle's coordination is caught off-guard and the capsule gets painfully jammed in the works. It is thought that the muscular ligamentum flavum does a similar thing on the other side of the joint and prevents the baggy capsule getting nipped as the spine recovers from the arched (extended) position.

The other intrinsic muscles, iliocostalis and longissimus, control the forward shear of the vertebrae although they operate at a more difficult angle when the spine is more deeply bent forward. Their

contracting ligamentum flavum contracting multifidus

Figure 1.27 With bending and straightening, ligamentum flavum and multifidus work right at the centre of movement to make sure the facet capsule does not get nipped in the joint.

contracting ligamentum flavum contracting multifidus

Figure 1.27 With bending and straightening, ligamentum flavum and multifidus work right at the centre of movement to make sure the facet capsule does not get nipped in the joint.

fibres pass in a direction closer to a back-front alignment. As the spine straightens they slide the vertebrae backwards in a reverse shearing action, rather like sliding drawers out of a chest. The deepest fibres of erector spinae muscles have a more transverse angulation than the superficial and they also contribute segmentally to controlling forward glide.

Figure 1.28 The direction of the fibres of iliocostalis and longissimus helps slide the vertebrae backwards as the spine straightens but their poor angle of pull makes their action weak.

The deepest tummy muscle, transversus abdominus, plays a unique role as it helps the spine straighten, because it works both as a tummy and back muscle at the same time. It originates from either side of the linear alba (the shallow groove running down the centre of the abdomen) and passes transversely around the waist below navel level, like a cummerbund. Either side at the back it joins a sheet of fibrous tissue, which performs a very important role, called the thoraco-lumbar fascia. The fibres of this fascial sheet make a diagonal lattice which attaches in different layers to both the transverse processes of the lumbar vertebrae.

Figure 1.29 Transversus abdominus constitutes the deepest layer of the tummy muscles. As a 'muscle-in-the-round' it performs two actions in one: drawing the belly in at the front and straightening the spine via tightening the thoraco-lumbar fascia at the back.

As the muscle contracts it creates a high pressure air bag in front of the spine (like any other tummy muscle). But it also tugs sideways on the thoraco-lumbar lattice. As the lattice pulls out laterally it becomes shallower in height which telescopes the cotton reels down on one another and tugs down on lateral spars of the vertebrae, thus clenching the spine.

relaxed thoraco lumbar lattice

Masculine And Feminine Tree Life

Figure 1.29 Transversus abdominus constitutes the deepest layer of the tummy muscles. As a 'muscle-in-the-round' it performs two actions in one: drawing the belly in at the front and straightening the spine via tightening the thoraco-lumbar fascia at the back.

tense and flattened thoraco-lumbar lattice relaxed thoraco lumbar lattice neurocentral core is compressed

As well as helping multifidus regulate forward bending, trans-versus abdominus performs the very important role of clamping of the spinal segments together in preparation for spinal activity. This ensures the spine doesn't jump out of joint as soon as other movements pull it about. This clamping works in all sorts of ways, from the subtle to the spectacular. For instance, it gathers up the spinal segments and allows us to turn over in bed at night without waking, but it also stiffens your spine automatically as you see the tennis ball coming at you over the net. It converts the lumbar segments into a stiffened pillar in anticipation for other things it has to do. With its tendency to weaken, no wonder these actions (to name but a few) are so painful with bad backs.

Recent research suggests that transversus abdominus is supported in keeping the segments stable by the ever-acting breathing muscle, the diaphragm. In an example of Nature's expediency, both take turn about in keeping the lateral tension on the thoraco-lumbar fascia. Since we breathe all the time I cannot imagine a better partner. What could be more appropriate than harnessing the breathing mechanism to assist another equally fundamental mechanism: keeping the central strut of the body intact.

It happens like this: the diaphragm attaches in part to the sides of the thoraco-lumbar fascia. It is a huge dome of contractile tissue which separates the thorax and abdomen, making both into watertight compartments. We take a breath in when the diaphragm contracts and flattens and descends in the chest. This increases the volume in the chest cavity but lowers the pressure, causing air to flow in through the nose. The contracting diaphragm tugs laterally on the sides of the thoraco-lumbar fascia, making each in-breath telescope the lumbar segments. As we breathe in, the low back is kept secure as we go about our business.

When it is time to breathe out the diaphragm relaxes, raising the pressure inside the chest compared to the outside, making air flow out. At the same time, the diaphragm hands over the reins to trans-versus abdominus which is active during the breathing out phase, but which also exerts tension on the thoraco-lumbar fascia. During expiration it shrinks the girth which automatically raises the intraabdominal pressure, helping to stabilise the spine.

Thus with each 'muscle' taking turns to keep the thoraco-lumbar fascia tense, we keep our backs stable just by breathing. This also explains why it so often hurts to cough with a bad back. The explosive exhalation happens with a strong involuntary contraction of the tummy which jerks the thoraco-lumbar fascia sideways. This bounces the vertebrae vertically and invariably elicits pain from the problem part.

The breathing control of the thoraco-lumbar fascia also explains why we automatically hold our breath when we lift. The held breath and the clenched tummy recruit both muscle systems simultaneously, raising the tone in the thoraco-lumbar fascia. The lumbar segments are held doubly secure.

This is exactly what weight-lifters do. As they bend to grasp the bar they take a sharp breath in and hold it, sucking their tummy in at the same time. Some professionals even wear a 'kidney belt' to reinforce the power of transversus abdominus, making it easier to generate the power to slot the lumbar vertebrae back on one another as the muscle pulls the spine straight.

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