Risk Factors Inherent in the Worker
When there is a mismatch between the physical requirements of the job and the physical capacity of the worker, workplace musculoskeletal disorders (WMSDs) can result.
Risk Factors - Worker
Age: The prevalence of WMSDs increases as people enter their working years (ages 25 to 65). By the age of 35, most people have had their first episode of back pain. Once in their working years, the prevalence is relatively consistent. Musculoskeletal impairments are among the most prevalent and symptomatic health problems of middle and old age.
Another problem is that advancing age and increasing number of years on the job are usually highly correlated. Older workers have been found to have less strength than younger workers, although hand strength does not appear to decline with aging.
Gender: Whether the gender difference seen with some WMSDs in some studies is due to physiological differences or differences in exposure is unclear. There are some anatomical differences between male and female bodies that may affect worker ergonomics when lifting. Generally, men tend to have greater upper body strength and larger muscle mass, while women have a lower center of gravity and wider hips. These differences may influence the lifting technique and the distribution of weight during lifting tasks. Another consideration is the potential for repetitive strain injuries, such as carpal tunnel syndrome. Women may be more susceptible to these types of injuries due to their smaller wrist size and differences in muscle strength and endurance.
Strength and Endurance: Muscular endurance is the ability of a muscle or a muscle group to remain contracted over a period of time. Static endurance can be determined by the length of time a limb can maintain a certain position. Dynamic endurance can be measured by the number of times a limb can perform a movement against a certain resistance. Muscular strength is the maximum amount of force that a muscle can exert under maximum contraction. The amount of force that can be exerted by the muscles in the arms, legs and back depends on body posture and the direction of force. For example, when standing, you can exert more force when pulling backwards than when pushing forwards.
Physical Fitness: The relationship of physical activity and WMSDs is more complicated than just "cause and effect." Physical activity may cause injury. Fitness, for most physical activities, is a measure of a combination of strength, endurance, flexibility, musculoskeletal timing, and coordination. In a study of male fire fighters, physical fitness and conditioning appeared to have significant preventive effects on back injuries.
The lack of physical activity may increase susceptibility to injury. A lack of physical activity after injury may increase the risk of further injury. The probability of injury increases as muscles weaken. Consequently, demanding repetitive or static muscular work requires energy, not necessarily strength. You may be strong, but not have sufficient energy to do the task.
- Isometric (Static) work: Static work occurs when the muscles remain contracted for an extended period of time with no movement, as in holding an object. Muscles do not get the chance to relax and can fatigue quickly.
- Isotonic (Dynamic) work: Dynamic work involves repetitive contraction and relaxation of the muscles and is less tiring and more efficient than static work. The motion of the muscles also help pump blood supplying oxygen and eliminating carbon dioxide.
Anthropometry: Workers come in all shapes and sizes, and so designing for only the "average" person in one group or segment causes problems for everyone else who does not fit into that group. Anthropometry is the science of studying the difference in body size and proportions by measuring various body characteristics, including weight, physical range of mobility, and body dimensions. Weight, height, body mass index (BMI) (a ratio of weight to height), and obesity have all been identified in studies as potential risk factors for certain WMSDs, especially Carpal Tunnel Syndrome (CTS) and lumbar disc herniation.
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6-2. By what age have most people experienced their first episode of back pain?
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