Improperly designed workplace environments frequently result in computer operators assuming work positions outside of an optimum neutral posture comfort zone. Significant medical and health considerations exist for advocating optimal neutral posture for seated workers.

These health considerationsprovide significant justification for, and a strong incentive to provide, ergonomically correct computer work environments.

Conservation of Energy

Approximately 70% to 80% of human energy is expended in the maintenance of the body's mass in space and the movement of the body's mass through space.
As a survival mechanism, humans have an innate desire to conserve energy. The least amount of energy expenditure occurs when the body's mass is maintained in a balanced position over its base of support.

Based upon anthropometric data, the human head weights between 8 and 14 pounds (proportionate to total body mass). The mechanical support structures for the maintenance of the head's position in space during dynamic movement or stationary postures, are the spinal vertebrae and disc; an intricate network of ligaments, cartilage and joint capsules, and numerous pairs of counterbalancing muscles in front, back and either side.

Optimal Work Posture - The Comfort Zone -

For seated workers, the optimal position of the head is in the neutral posture, which means that the head is centered over the midline of the body when viewed from either the antero-postero or lateral plane, or with a slight (normal) forward lean (5*). The neutral posture places the smallest demand on energy expenditure and results in the least amount of structural stress and related fatigue.

The neutral posture also helps to preserve the normal antero-postero arc of the cervical spine (neck vertebrae). The four counterbalancing antero-postero arcs of the spinal column are designed to absorb shock and reduce structural and gravitational stress on the spine, which serves to protect the brain stem, spinal cord and attached network of the spinal nerves and their functions.

Visual Considerations

While maintaining the head in its optimal, neutral posture, relaxed vertical and horizontal eye movements can occur up to 35 degrees without significant movement of the head away from neutral.

Abnormal Work Postures - Faulty Biomechanics -

Static work postures that require a shift of the head away from the neutral posture, either in flexion, extension, rotation or lateral flexion to the right or left, result in imbalanced, asymmetrical muscle loading.

When unbalanced static muscle loading is experienced repeatedly and for prolonged periods, it results in a build-up of toxic waste products within the muscle chemistry, causing fatique and loss of efficiency. In addition, abnormal work postures produce asymmetrical compression on spinal discs and excessive mechanical stress on the supportive ligaments and joint capsules.

Over time, the consequences of asymmetrical spinal loading can result in degenerative disc and joint disease with resultant irritation and inflammation of the nerves that exit from the openings on either side of the vertebrae. The nerves in the neck region provide the sensory and motor contral to the back of the skull, neck and upper back muscles, shoulders, elbows, forearms, wrists, hands and fingers. These nerves also regulate the blood and lymph circulation, providing oxygen and nutrients to and waste product removal from these tissues.

Medical Considerations

Human factors engineers (ergonomists) as well as physicians involved in the diagnosis and clinical management of the common neuromusculoskeletal disorders of seated workers have long recognized the correlation of faulty work posture and a variety of painful and often temporarily disabling syndromes relating to the cervical spine. Among these disorders are tension, migraine and cluster headaches; neck stiffness, pain and spasm; back pain; thoracic outlet syndrome; infraspinatous, scalenus anticus and pronator terres syndromes; shoulder, elbow, forearm and wrist tendonitis and entrapment disorders of the wrist and hand, including carpal tunnel syndrome. There is an extensive field of publised scientific literature supporting the above clinical correlation.

It is common for employees, supervisors and health care providers to misdiagnose carpal tunnel syndrome when in reality the synptomes can be a manifestation of combinations of the above spine related disorders, often caused by or aggravated by faulty work postures among sedentary workers.

An Aging Population of Workers

The neuromusculoskeletal conserns expressed above are currently particularly relevant with our aging population of sedentary workers. Neck pain and striffness, upper spinal stress, headaches and upper extremity disorders are often provoked or aggravated in middle age workers who transition from single lens to bifocal or trifocal eyelasses. To accommodate the mid-range visual need to focus on information provided on computer monitor screens, workers often extend their neck into undesirable, stressful postures.