It is probably fair to say that every worker who lifts or does other manual handling tasks is at some risk for musculoskeletal injury. Low back injury is the most likely kind of injury. The complete elimination of this risk is not realistic because MMH usually involves awkward postures and repeated forceful movements. However, people can reduce the number and the severity of manual handling-related injuries substantially by using safe work practices.
To prevent occupational back injuries, it is essential to identify the factors of MMH that make the worker more susceptible to injury or that directly contribute to injury.
When efforts to prevent injuries from MMH focus on only one risk factor, they do not significantly reduce the injury rate. A more successful approach such as the one offered by ergonomics combines knowledge of engineering, environment, and human capabilities and limitations. The following aspects should be considered:
Often, poor planning of the work flow results in needless or repeated handling of the same object. When articles are temporarily stored in one place, moved to another, stored again, and moved again, a more efficient work flow can eliminate many potentially harmful MMH tasks.
The design or redesign of jobs involving MMH should be approached in the following stages:
Consider using powered or mechanical handling systems if eliminating MMH tasks completely is not possible. Mechanical aids lower the risk for back injury substantially by reducing the worker's physical effort required to handle heavy objects.
Manual handling such as lifting and carrying can be easier and safer if mechanized by using lift tables, conveyors, yokes or trucks. Gravity dumps and chutes can help in disposing of materials. Mechanical aids also reduce the need to select workers for the task, but it is essential that the worker is properly trained in the safe use of the available equipment.
Where possible, use mechanical aids. The next step is to decrease the manual material handling demands. There are several ways to achieve this:
It is important that the design of MMH allows the worker to do tasks without excessive bending and twisting. These body motions are particularly dangerous and can cause back injury even when not combined with handling loads.
Pace of work, particularly when externally imposed, may significantly contribute to the worker discomfort, and consequently to the onset of musculoskeletal injuries, including low back injuries. As a rule, pressure to work at a certain pace coming from management creates the mental need to work in a hurry. This in turn creates tension not only in the mind but also in the body. Tensed muscles are much more prone to injury, leading to WMSD.
Very recent research on the causes of back injury shows that workers at high risk for back pain (for example, those who lift for a living or where lifting is significant part of their job) need more frequent and longer breaks. Even a moderate pace of lifting (not necessarily at the maximum lifting limit) if maintained for a prolonged time without breaks, rapidly decreases workers' lifting ability by speeding up their fatigue. It also means that in the second half of the working day, the risk for contracting low back injury (and, for that matter, any other musculoskeletal injury) is higher. And because of this it would be wise to assign heavier tasks at the beginning of the working day rather than at the end (but after the worker is "warmed up").
It would be ideal if workers could work at their own pace and have some freedom to take a rest break when they start feeling the effects of fatigue. However, this might be impractical. It seems reasonable to incorporate two additional 15-minute breaks, mid-morning and mid-afternoon, in addition to the 30-minute lunch break, If that schedule is still not feasible, shorter but more frequent breaks can do as well.
It is also important that novices whose jobs involve lifting and MMH be given time to adjust by allowing them more breaks.
The design of the work environment is an important element of back injuries prevention.
When the MMH tasks are done outdoors, the temperature conditions including the humidex (in hot weather) or wind-chill factor (in cold weather) have to be monitored very closely.
The objective of pre-placement screening is to select individuals less likely to be injured in work involving MMH. X-rays, medical examination, physiological testing may be hazardous under certain circumstances or may not be specific enough to achieve the intended objective. They do not reduce the occurrence of occupational back injury among selected individuals. Worse, the selection procedures can be abused when applied as a substitute for work design.
The only situation where pre-placement screening may be justified as a preventive measure is where a job involves heavy MMH in an unpredictable and uncontrollable environment. Examples of these are firefighting, mine and water rescue, and police work. Even here, the selected tests should closely reflect with the anticipated requirements of the job. By far the best pre-selection method, if one must be used, is performance of the actual task.
There is little evidence to indicate that training alone reduces the number of MMH injuries. When combined with work design, training is an important element in the prevention of injuries. Proper training also shows the worker how to actively contribute to the prevention of injuries. A good training program should:
Instruction on how to lift "properly" is the most controversial issue concerning training in MMH. There is no single correct way to lift because lifting can always be done in several ways. Because of this, on-site, task specific training is essential. In fact, it is sometimes safer to allow the worker to use common sense acquired by experience rather than to force new biomechanically correct procedures. But there are some general lifting rules.
It is also important that workers:
Finally, there is an aspect of training that cannot be overlooked if training is to be part of an effective prevention program.
Workers should be educated that muscles, tendons and ligaments are not prepared to meet the physical stress of handling tasks when they are not "warmed up." They are more likely to pull, tear or cramp when stretched or contracted suddenly under such conditions. This, painful enough by itself, can lead to more serious and permanent injury if physically stressful work is continued. Warming up and mental readiness for physically demanding tasks are important for any kind of MMH, but particularly for occasional tasks where the worker is not accustomed to handling loads. Workers are more likely to have "ready-to-go" attitude for the task ahead when they understand that other preventive measures are also tried.
Document last updated on March 7, 2007