A second key characteristic of the pelvic ring is that its degree of tilt determines the quality of the curves in the spinal column above. Any change in the angle of the sacral portion of the pelvis will influence the curves of the spine above, thus determining posture. If the pelvic ring is in a balanced position, the spinal curves will be proportionately balanced and the posture safe. If, however, the pelvic ring is abnormally tilted, poor posture will result and the spine will consequently be more vulnerable to injury and pain.
Fig. 4. The pelvic ring
Good posture and smooth movement and rhythm require good coordination between nerves and muscles, good flexibility of tissues and adequate functioning of all joints involved.
Muscular Supports
The chief back muscles are as follows:
The erector spinae muscles form two columns, one on each side of the spine. They extend the spine and keep the trunk erect.
The latissimus dorsi is a broad, flat muscle lying over the lower part of the chest and loins (between ribs and hip bones). It draws the upper bone of the arm (humerus) down and back, and rotates the arm inwards.
The gluteal muscles, which form the buttocks, raise the trunk from a stooping to an erect position. They are also involved in leg motions.
The sling muscles (hip flexors) connect the transverse processes of the spine on the inside (the projecting pieces of bone mentioned in the section ‘Spinal Units’), cross the pelvic ring and attach to the thigh bones just below the hips. They are very important in the maintenance of upright posture.
The lateral muscles are situated between the ribcage and the pelvic ring. They extend from the lowest ribs to the hip area and legs.
Secondary Supports
Muscles forming secondary supports to the spine are: the quadriceps (thigh muscles), which run down the front of the thighs and insert into the kneecaps or patellae, and serve to extend the knees; and the hamstrings, which are located at the back of the thighs, passing from the pelvic ring and inserting into the bones of the lower legs (tibiae and fibulae). The hamstrings flex the knees and extend the thighs.
Both sets of muscles – quadriceps and hamstrings – contribute to the tilt or balance of the pelvic ring and so are important to good posture.
The abdominal muscles, which will be dealt with in chapter six, basically extend from the breastbone (sternum) to the symphysis pubis, on each side of the midline. Although thin, these muscles give extremely important support to the spine. They operate at a distance and so provide leverage.
Postural patterns are influenced not only by lifestyle but also by genetic and early environmental factors. Without conscious, sustained effort, faulty postures can become permanent.
There is no ideal posture, since people come in all shapes and sizes. The ideal posture for you is one in which your back is subjected to the least possible strain and in which the normal graceful curves of the spine are maintained.
The key to good posture is fitness. If you keep your muscles well conditioned, you stand a good chance of acquiring the posture that is correct for you, particularly if you complement this with a balanced mental and emotional state. This is the essence of the yoga approach.
Dr Bess Mensendieck, a sculptor turned physician, has remarked that correct posture, and freedom from pain due to faulty posture, can be acquired only when all muscles are used in accordance with their anatomical functions and with the laws of body mechanics. She has further noted that the primary exercise needed to achieve these states is the practice of correct postural habits during normal daily activities. No daily half-hour exercise session alone will produce good posture if muscles and joints and related structures are not used properly the rest of the time.
A well-aligned vertebral column when we are upright or sit or lie down imposes the least strain on the spine. It is also an important prerequisite for the harmonious functioning of the nervous system, which is hinged on the backbone and the spinal cord, and for the free expansion of the chest to permit proper breathing. If we can maintain natural physical equilibrium when both sitting and standing, we minimize strain on the back muscles and facilitate harmonious distribution of the body weight along the 132 articulations of the vertebral column.
In summary, your posture is determined by the way you hold each part of your body, from head to toes. Your posture affects your breathing, indeed your health in general – both physical and emotional – and the image your present to the world.
In order to relieve stress on the lumbar spine, a natural lumbar curvature (at the small of the back), good balance and flexibility must be maintained at all times. The natural lumbar curvature is maintained through pelvic tilt (assisted by tightening abdominal and buttock muscles). The position distributes weight evenly down through the spine allowing the strong leg muscles to bear the weight.
Now that you have a basic understanding of the structure and function of the spine, you will readily appreciate the principles of good body mechanics which follow and the importance of maintaining the normal spinal curves.
Sitting
Good posture when sitting puts the pelvis in a neutral position, that is, neither tilted backwards not tilted forwards (remember that posture is controlled mainly from the pelvis).
The spine should be supported along its natural curve. The height of the seat should be such as to place the knees level with, or higher than, the hips (Fig. 5).
Figures 6 and 7 are examples of poor posture in sitting. In Fig. 6 the pelvis is tilted backwards. This flattens the normal curve of the lower spine, stretching ligaments and eventually producing pain.
Fig. 5. Good posture in sitting
Fig. 6. Poor posture in sitting
Fig. 7. Poor posture in sitting
In Fig. 7 the pelvis is tilted forwards, thus distorting good posture in much the same way as prolonged standing does. This, too, can lead to back strain and pain.
The Easy Pose
One excellent way to sit is in the yoga Easy Pose (Fig. 8). It provides a stable base, encourages you to hold your spine naturally erect and promotes relaxation of the back muscles. It brings into play the sartorius, or tailor, muscles which lie across the thighs, from about the front of the hip bones to what we know as the shin bones. These are the muscles used in bending the legs and turning them inwards.
Fig. 8. Easy