Muscle Tone and Posture
The natural gaze of a human is between 15 and 20° downward with a straightforward gaze. This adaptation allows us to see where we’re walking.- very handy unless you need to look up. Looking up is stressful. Almost anything above 5 – 10 degrees requires you to re-orient you neck. This makes the focus more comfortable, but creates stress in the neck and upper back.
Over time the body can become habituated to postures that are held for prolonged periods or are frequently used - some muscles perennially lengthened, others shortened. This accommodation of the body to a stressful posture affects not only how the head is carried, but the resting posture of the back and how each curve of the back reacts to movement and stresses.
Eyes guide posture. Try turning your head to one side and hold the position. Pay attention to how your trunk feels. Do you feel changes in the tensions in your upper arms? Now turn your head to the other side and feel your truck muscles again.
Bring your chin toward your chest and feel what it does to the muscles in your back. Bring it back to the midpoint, and then slightly hyperextend so that your chin is angled towards the ceiling. Pay attention to changes in the muscle balance in your shoulders and back. Did the curves in your back actually change position? For many people they do.
Some of the earliest human reflexes to develop in babies are induced by neck position. Two of these are the symmetrical and asymmetrical tonic neck reflexes.
Symmetrical Tonic Neck Reflex::
With the head centered on the body, the Symmetrical Tonic Neck reflex is triggered by moving the chin toward the chest or moving the chin away from the chest. As the chin moves down toward the chest, arms and legs flex. This creates a sort of balled up position – arms close to the body, elbows flexed while both hips and knees are flexed drawing the legs up towards the center of the body. When the neck returns to the center or to an extended position, the arms and legs extend. The right and left sides of the body are mirror images. This reflex is called ‘symmetrical because if affects both legs and arms and affects right and left in the same manner,
Asymmetrical Tonic Neck Reflex::
The Asymmetrical Tonic Neck reflex is triggered by head rotation, or turning the chin towards the right or left. Turning the head to the left, the left arm and leg extend while the right flex. Turning the head to the right, the opposite reaction occurs. This reflex is called ‘asymmetrical because the right and left have opposite reactions. When one side flexes, the other side extends.
By one year of age, most children have integrated these reflexes – that is, they are not controlled by them. As adults, these are generally under control unless there has been a traumatic injury. Even then, integration is generally quickly restored. None the less, postural tone is influenced by these reflexes and other very basic reflexes.
Muscle tone is difficult to describe. Although it may be related to muscle strength and condition, it is not the same. It’s sort of like the blank canvas your movement and action plays against. Normal tone runs a large gamut, from very loose to fairly taut.
The normal tone of your muscles may affect how easy it is for you to change techniques or to do tasks in a specific manner. To some extent, the background tone of your muscles will affect how prone you are to injury and what types of interventions (tools) will work for you. It also may play a part in placement of the monitor, chair choice and adjustment, and recommendations regarding keyboard height.
Understanding of muscle tone is one part of the Ergonomist’s toolkit. In looking for ergonomic solutions, awareness of tone, what it feels like and what types of things make it change (body awareness) is prime. Muscle tone will be revisited in many future articles.