Widespread mechanization and automation have affected virtually every sector of the Canadian economy. From offices to industry, new technologies have changed the way people do their jobs. Machines are now doing work previously done manually. More and more people work in a sitting position to operate these machines.
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.
Injuries resulting from sitting for long periods are a serious occupational health and safety problem. This problem will likely become more common in the future because the trend toward work in a sitting position is still increasing.
When the employee can alternate sitting with other body positions, sitting at work is not 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 such physically demanding jobs 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.
Sedentary employees may also face a gradual deterioration in health (if they do not exercise or do not lead a physically active life). Prolonged sitting drops the employee's physical activity to the lower limit needed for healthy-body functioning. The most common health problems that employees suffer are disorders in blood circulation and injuries affecting their ability to move.
There is 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. The result can be swollen or numb legs and eventually varicose veins. Also, a reduced blood supply to the muscles accelerates fatigue. This is why an employee who sits all day long doing little physical work often feels 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 on certain regions of the body. The neck and lower back are the regions usually most affected. Why? Prolonged sitting:
Employees, who for years spend most of their working time seated, also experience other, less specific adverse health effects. Decreased fitness, reduced heart and lung efficiency, and digestive problems are common. Although these conditions are not diseases or injuries themselves, they do predispose the employee to other diseases.
A poor body position is largely responsible for the ill effects of prolonged sitting. Poor body positions can also originate from an unsuitable job design that requires employees to sit uninterrupted for longer than one hour. The duration of sitting, along with the shape of the body in a sitting position, is the most critical risk factor in work in a sitting position.
An unsuitable work space that prevents employees from sitting in a balanced position can cause poor body positions. The physical arrangement of work space elements such as work surfaces, tools and equipment may not correspond with the reaches and clearances of seated employees. The workstation may also be unsuitable because the chairs are too high or low for an employee's body size and shape.
Improper or inadequate training can also lead to poor body positions. Employees may be unaware of the health hazards of sitting jobs because they are not as obvious as those of strenuous jobs. As a result, employees may not know which practices to avoid and which ones to adopt.
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" work. So, a good sitting position is one that allows employees to change their body positions frequently and naturally when they want without being restricted by the work station or job design.
Perhaps the best description of a "good" position is a set of naturally chosen body positions that fall within an acceptable range. A workstation that allows frequent changes and more mobility allows an employee to have a more natural and healthier work pattern.
Recommendations on how to sit properly are not compulsory. Sometimes, it is acceptable to deviate with outstretched or cramped positions to relieve muscle tension.
A "good" sitting position at work can be achieved only by focusing efforts on the three areas that are identified as potentially hazardous:
None of these areas is more important than the other, and none of them alone can bring about substantial improvement.
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:
Before considering the requirements for the design of a workstation and a chair, take into account the anticipated tasks. The work may require visual, manual, or foot tasks, or combinations of these. Each of these types of tasks requires different modifications in work station design.
Visual tasks place tension on the neck, trunk and pelvis so that the eyes can achieve and maintain the required vision for a needed duration of time. It is important that the design of the work station reduces the strain on the neck. In some work situations it is possible to do this by properly positioning the visual tasks. Where this is not possible, work schedules should shorten the amount of time employees spend on each task.
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.
The chair should always be considered as an integral component of the workstation and not in isolation. The other workstation components, such as the desk and VDT (computer), workbench or panel in a control room all affect the employee's body position. They, together with a chair, make it possible to work in a balanced 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. The only solution is to provide the employee with a fully adjustable chair that can accommodate the maximum range of people (typically 90 to 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.
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.
The "ergonomic" chairs now available are designed for a range of people, but not always for one person in particular. Nor are they designed for any specific tasks or arrangement of the work station. Therefore, purchasing a chair because it is labeled "ergonomic" can be a mistake. The chair becomes ergonomic only when selected to suit the employee's or a group of employees' body dimensions, particular workstation, and tasks.
No matter how well the workplace is designed, an employee who sits for long periods will suffer discomfort. The main objective of a job design for a seated employee is to reduce the amount of time the person spends "just" sitting. Frequent changes in the sitting position are not enough to protect against blood pooling in the employee's legs.
Five minutes of a more vigorous activity, such as walking for every 40 to 50 minutes of sitting, can protect an employee from swollen legs. These breaks are also beneficial because they give the heart, lungs and muscles some exercise to help counterbalance the effects of sitting for prolonged periods in a relatively fixed position. 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. No matter how good the workplace and the job designs, there is always need for individual tailoring. Consultation with employees can secure their active participation and personalize their work.
Individual work practices, including sitting habits, are shaped by proper training. Training should encourage employers and employees to adopt methods that reduce fatigue from too little and too much a workload. It is important to acknowledge that some traditional ideas, such as "sitting work is light work" or "people work harder standing," are mistaken.
Training should also explain the health hazards of prolonged sitting and give recommendations on what a worker in a given workplace 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.
Training should also emphasize the importance of rest periods for the employees' health and explain how active rest can do more for keeping employees healthy than passive rest. The effect of such training can reach far beyond occupational situations because the employees can apply this knowledge also in their off-job life.
Document confirmed current on October 6, 2010
Document last updated on June 19, 1998