Exercise cannot take place without muscle contraction. The muscles of the body are suspended on a framework that ultimately leads back to the spinal column, known as the pillar of support for the movement.
Although the spinal column and its vertebrae form one supportive structure, individual parts can be hurt or damaged through incorrect movements associated with some exercises. This is less likely to happen if you are well-informed about the anatomy of the spine and you apply this knowledge when exercising.
The spinal column has four regions:
- Cervical: the neck region, which supports the head.
- Thoracic: the chest region, which has attachments for the ribs and protects the heart and lungs.
- Lumbar: the lower five vertebrae, which support the upper body and the pelvis.
- Sacral: the lowest area, made up of a triangular bone consisting of five fused vertebrae and connected to the pelvis and the entire vertebral column.
The forward and backward curves of the spinal column provide greater resistance to compression, as well as giving the spine both static strength and the ability to make dynamic movements, in order to satisfy the conflicting demands of structural strength and freedom of movement the body must increase the complexity of the joint structure.
The thoracic region has a curve going backward (called a convex kyphosis), while the forward curves of the cervical and lumbar regions are called a concave lordosis. These curves can become exaggerated when posture is poor, particularly in the lumbar area, causing back problems.
It is especially important for all exercisers to understand the anatomy and biomechanics of the lumbar spine. Each of the bones in your spine is called a vertebrae. Depending on their function, vertebrae vary in size and alignment.
Each lumbar vertebra is made up of two parts. The first is the vertebral body, the larger part, situated anteriorly (towards the front). This part of the vertebrae is supportive, weight-bearing, absorbs shock and provides flexibility.
The second part is the vertebral arch, horsey shoe-shaped, and situated posteriorly (towards the back). It has a long bit of bone sticking out of it, and this is the lumps that you feel when you run your hands down the middle of your back.
The vertebral arch is non-weight bearing and protects the elements of the central nervous system, and provides attachments for vertebral ligaments and muscles.
The intervertebral discs function like the suspension of your car. These discs are small pads that lie between the vertebrae and act as shock absorbers for downward forces as well as providing mobility in the lumbar region.
The mechanism may be compared with the swivel-like movement that can occur when a tennis ball is placed horizontally between two flat pieces of wood.
The disc has a soft, spherical center that is predominantly water which maintains a space between the vertebral bodies. This nucleus is incompressible but can be deformed, although its volume is always the same its shape may alter.
This center is surrounded by a tough fibrous ring much like the cross-section of an onion that radiates and dissipates downward pressures on the spine and maintains the position of the entire disc unit.
The intervertebral discs have the following functions:
- to increase height by adding to the length of the spine;
- to join vertebra together and increase flexibility;
- to distribute weight evenly over the body of the vertebra;
- to act as a shock absorber;
- to maintain distance between the facet joints;
- to maintain the size of each individual intervertebral foramen.
The facet joints are the real joints in the spine that control movement. They are like tiny wings sitting out to the side of each vertebra. The position of each facet joint varies in each region of the spine.
The direction and the plane of the facet joints determine which movements are allowed and restricted.
The back muscles that lie closest to the surface have little to do with moving the lower back. They consist of the large flat latissimus dorsi (lats), the large flat trapezius (traps), and the rhomboids major and minor (shoulder-blade muscles).
As a group they use the spinal column as a base of support for moving the arms and shoulders. The muscles that move the spinal column can be divided into two groups: those that lie towards the back and those that lie towards the front (the abdominals).
When you move your lower back you mainly involve the deeper back muscles (the erector spinae) and the abdominals. The deep back groups of muscles lie on both sides of the vertebral column and for ease of description are named as one muscle — the erector spinae. It is easy to see where they got their name — they help to erect the spine, or keep it upright.
These muscles form the bulky mass that starts on the pelvis and travels up each side of the spine, inserting in a multitude of positions up and down the spine, like a series of guy ropes extending the entire length of the spine, or a group of those spitfire grubs that you see massing on gum trees.
The erector spinae is important in posture because it contracts gently to counteract the swaying movements that normally occur in the upright position, but strong contractions of the erector spinae will extend the trunk.
The erector spinae helps to pay out the spine during forward bending and then to pull it back upright; however, electrical studies have shown that the erector spinae switches off in both relaxed seating, standing, and full-forward bending — in these positions we rest on our ligaments. That is why we avoid forward bending positions in exercises these days.
Because the spinal column moves like the shaft of a crane, control between individual vertebrae is important. This control is provided by the shorter muscles of the erector spinae. Without this, the column would buckle and collapse when it moves. The erector spinae is a speed-control and range-of-motion muscle; that is, a postural muscle, not a power muscle. That is why we knowledgable exercise instructors avoid all those fast twisting movements of the spine.
Control of extending the lower back is largely dependent on the activity of the abdominal muscles. The abdominals are a group of four muscles: the rectus abdominis, the transversus abdominis, the external oblique, and the internal oblique. All attach the rib cage to the pelvis. They are responsible for alterations in the curvature of the lower back, and also for the bending and twisting of the trunk.
The flat muscle in the front (the rectus abdominis, or washboard, or 6-pack) is largely responsible for forward, bending or flexion, whereas trunk rotation is brought about by contraction of the external oblique on one side and the internal oblique on the other. However, when exercising the abdominals have two important functions that can be utilized to protect the lumbar spine and reduce the biomechanical stresses acting on it.
Weak abdominals allow the pelvis to tilt forwards, which exaggerates your lumbar lordosis. At rest, the abdominals are moderately involved in supporting the vertebral column but contract to the maximum when the lower back is consciously flattened, or if they are involved in the exercise. Assisted by other muscles, the abdominals can act together to tilt the pelvis towards the back, which in turn flattens the lumbar spine.
This function is important because the abdominals can act together to maintain normal lordosis, and can be used during exercise to brace the lumbar spine, protecting it from excessive force. You need to consciously contract your abdominals whenever you are exercising, not just when you are lying on the floor.
If the abdominals are contracted during lifting, or when air is taken in, the abdominal pressure increases and transforms the abdominal cavity into a rigid barrel. This action of the abdominals reduces compression on the discs between the vertebrae by 30 percent in the area between the lowest lumbar vertebra and the first sacral vertebra of the pelvis. It also decreases by 55 percent of the forces exerted by the erector spinae.
Ligaments in the spine are bands that attach bone to bone and limit the degree of movement between two bones. The nature of the attachments and a large number of spinal ligaments increase the stability of the lower back, but excessive demands and incorrect techniques during exercise may raise the risk of strain or rupture.
Biomechanically, the two most important ligaments to consider are the anterior longitudinal ligament and the posterior longitudinal ligament.
Back arching is limited by the anterior longitudinal ligament (the one at the front). In an upright stance the posterior longitudinal ligament (the one at the back) tends to take most of the strain. The range of forward bending is dependent on the extensibility of this ligament and is controlled by the mobility of the joint, the flexibility of the discs, and the elasticity of the muscles.
The posterior longitudinal ligament is, however, 50 percent weaker than its anterior counterpart and less extensive, particularly in the lumbar spine. Together, these factors predispose the lumbar spine to weakness, often exacerbated by certain exercise conditions.
Think of your spine as being-like the Centrepoint Tower in Sydney. Just as support wires hold up this tower and anchor it to the ground, ligaments connect the lumbar vertebrae to the pelvis. These ligaments increase the stability of the long vertebral column which only has a small base of support. However, they do limit the degree of flexion and extension, and even more the amount of lateral flexion (side bending).
You can now really see how complicated the spine is, and how important it is for instructors to understand the functioning of the spine before they start showing others how to exercise. A little of the wrong exercises and you may end up with a lifetime back injury.