Working in a Sitting Position - Overview

Injuries or illnesses resulting from sitting for long periods are a serious occupational health and safety problem. Sitting jobs require less muscular effort, but that does not exempt people from the injury risks usually associated with more physically demanding tasks. For example, clerks, electronic assembly-line employees, and data entry operators who work in a sitting position also suffer back pain, muscle tenderness, and aches. In fact, reports of varicose veins, stiff necks, and numbness in the legs are more common among seated employees than among those doing heavier tasks.

In addition, sedentary time has been found to be associated with health effects such as metabolic syndrome (including diabetes), heart disease, and poor mental health.

When the employee can alternate sitting with other body positions, sitting at work may not be as large a risk for injury or discomfort.

For those who have no choice and must sit for long periods, the situation is different. Although sitting involves less muscular effort than physically demanding job tasks such as gardening or floor mopping, it still causes fatigue. Sitting requires the muscles to hold the trunk, neck, and shoulders in a fixed position. A fixed working position squeezes the blood vessels in the muscles, reducing the blood supply to the working muscles just when they need it the most. An insufficient blood supply accelerates fatigue and makes the muscles prone to injury.

There is also less demand on the circulatory system due to the limited mobility while sitting. As a result the heart activity and the blood flow slow down. Maintaining a steady upright body position while sitting further decreases blood circulation.

An insufficient blood flow, specifically blood that is returning to the heart from the lower legs, causes blood to pool. Pressure on the underside of the thighs from a seat that is too high can further aggravate this issue. The result can be swollen or numb legs and eventually varicose veins. Also, a reduced blood supply to the muscles accelerates fatigue. This lower blood supply explains why an employee who sits all day long doing little physical work often feel tired at the end of a work shift.

Limited mobility contributes to injuries in the parts of the body responsible for movement: the muscles, bones, tendons and ligaments. Another factor is the steady, localized tension in certain regions of the body. The neck and lower back are the regions usually most affected. Why? Prolonged sitting:

• reduces body movement making muscles more likely to pull, cramp, or strain when stretched suddenly,
• causes fatigue in the back and neck muscles by slowing the blood supply and puts high tension on the spine, especially in the low back or neck, and
• causes a steady compression on the spinal discs that hinders their nutrition and can contribute to their premature degeneration.

A poor body position is largely responsible for the ill effects of prolonged sitting. The duration (length) of sitting, is also a risk factor.

Poor body positions can also originate from:

• job design that requires employees to sit uninterrupted for longer than one hour
• a workspace that prevents employees from sitting in a balanced position
• the physical arrangement of workspace elements such as work surfaces, tools, and equipment that do not correspond with the reaches of seated employees
• chairs that are unsuitable (e.g., too high or low, not adjusted correctly, etc.) for an employee's body size and shape

For each major joint such as the hips, knees, and elbows, there are ranges within which every healthy person can find comfortable positions. These positions should not impede a person's breathing or circulation, interfere with muscular actions or hinder the normal functions of the internal organs. Varying these positions is the essence of "good sitting". So, good sitting position is one that allows employees to change their body positions frequently and naturally within an acceptable range, and when they want without being restricted by the work station or job design.

A good sitting position at work focuses on the three areas:

• workplace design (including tasks, workstation, and chair design)
• job design
• education and training

None of these areas is more important than the other, and none of them alone can bring about substantial improvement. Recommendations on how to sit are not compulsory. Sometimes, it is acceptable to deviate with outstretched or cramped positions to relieve muscle tension.

The workplace design should enable the employees to carry out work in comfort and safety while allowing them to make voluntary changes in the working posture. To achieve this, the design should include the following elements:

• tasks
• workstation
• chair

Take into account that the work may require visual, manual, or foot tasks, or combinations of these. Each of these types of tasks requires different modifications in workstation design.

Visual tasks place tension on the neck, trunk, and pelvis so that the body maintains a position where the eyes can achieve and maintain the required vision for a needed duration of time. It is important that the design of the workstation reduces the strain on the neck. This setup involves positioning the focus of the work at an acceptable viewing angle, depending on the circumstances. For example, a computer workstation should have the monitor positioned just below eye level.

Both the movement and the forces involved in manual tasks affect body position. For light manipulating tasks, wrist and arm support may help. For heavier tasks, it might help to arrange the work surface below the employee's elbow height. The arrangement of the work station should allow the employee to keep the spine vertically aligned while exerting force. The employees should not have to lift and transfer loads horizontally.

Employees doing foot tasks should have pedals located directly in front of them to prevent their hips from twisting. It is important that employees are able to support their body evenly.

All workstation components, such as the chair, desk and computer, workbench or panel in a control room all affect the employee's body position. A work station should also allow for frequent changes between a variety of body positions.

A basic rule of ergonomics is that there is no such thing as the "average" person; however, providing an individually designed chair for every employee is not practical or possible.  A solution is to provide the employee with a fully adjustable chair that can accommodate the maximum range of people (typically 95 percent of the population). The chair must have controls to allow easy adjustment of the seat height and tilt, as well as the backrest height and angle. It is important that the employee can operate these controls from a sitting position. The chair's design must match the tasks.  For individuals outside the adjustable range of the chair, determine if alternative chairs can be made available.

A trial period is essential to the process of selecting a chair. Employees should try out the chair in the real work situation and ensure it meets the needs of the job before the final selection is made.

Please also see the OSH Answers document "Ergonomic Chair" for more information.

No matter how well the workplace is designed, an employee who sits for long periods can suffer from discomfort or negative health effects. The main objective of a job design in this situation is to reduce the amount of time the person spends sitting still. However, while frequent changes in the sitting position are good, they may not be enough to protect against prolonged sitting effects such as blood pooling in the employee's legs.

Five minutes of a moderate to vigorous activity, such as walking for every 40 to 50 minutes of sitting, can help protect an employee. These active breaks are also beneficial because they give the heart, lungs, and muscles some exercise. Where practical, jobs should incorporate "activity breaks" such as work-related tasks away from the desk or simple exercises which employees can carry out on the worksite.

Another important aspect of job design is feedback from employees. Consultation with employees can help tailor the solutions to the individual and personalize their work.

Individual work practices, including sitting habits, are influenced by proper education and training. Encourage management and employees to adopt methods that reduce fatigue and poor (static, awkward) posture.

Explain the health hazards of prolonged sitting and give recommendations on what employees can do to improve the working position. Employees need to know how to adjust the workstation to fit their individual needs for specific tasks. They also must know how to readjust the workstation throughout the day to relieve muscular tension.

Emphasize the importance of rest periods for the employees' health and explain how active rest (i.e., involving movement) can do more for keeping employees healthy than passive rest (i.e., more sitting). The effect of such training can reach far beyond occupational situations because the employees can apply this knowledge also in their off-job life.