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Course 711 - Introduction to Ergonomics

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Risk Factors Inherent in the Worker

workers

Introduction

It's important to understand that each worker's ability to respond to external demands of a task is different and unique. Basically, workers are all individuals and they should not be lumped together into groups. As the studies show in this module, results are inconclusive, and stereotyping or making generalities about an employee's ability should not be based on factors such as age, gender, or strength.

For instance, when lifting a load, the level from which loads are lifted, the duration of the lift, and frequency of the lift are all critical factors that influence loads imposed on tissues and the likelihood and severity of cumulative trauma disorders (CTDs).

However, muscle recovery time and the general physical condition of the worker may also be factors. That's why it is so important to consider the unique factors inherent in each individual, rather designing work based on generalities. When it comes to ergonomics, nothing is "written in stone".

The Musculoskeletal System

The musculoskeletal system is made up of the soft tissue and bones in the body. Below are the basic parts of the musculoskeletal system.

arm
  • Bones: the load-bearing structure of the body.
  • Muscles: tissues that contract to create movement.
  • Tendons: tissue that connects muscles to bones.
  • Ligaments: tissue that connects bones to bones.
  • Cartilage: tissue that provides cushioning and reduces friction between bones.
  • Nerves: the communication system that links muscles, tendons, and other tissue with the brain.
  • Blood vessels: tubes that circulate nutrients throughout the body.

Work Station Criteria

The following personal risk factors may be generalized across populations. It's important to understand that when designing a workstation or procedure it should be designed for the specific individual working at that workstation. Below are criteria that should be considered.

Age

age

The prevalence of CTDs 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.

Nonetheless, age groups with the highest rates of compensable back pain and strains are the 20-24 age group for men and 30-34 age group for women. In addition to decreases in musculoskeletal function due to the development of age-related degenerative disorders, loss of tissue strength with age may increase the probability or severity of soft tissue damage from a given injury.

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. In one study, average hand pinch and grip scores remained relatively stable in their population with a range of 29 to 59 years. Other studies have reported a lack of increased risk associated with aging.

Work Station Criteria (Continued)

Gender

age

Whether the gender difference seen with some MSDs in some studies is due to physiological differences or differences in exposure is unclear. One 1991 study found no gender difference in workers compensation claims for Carpal Tunnel Syndrome (CTS). Another study found no gender difference in reporting of neck or upper extremity MSD symptoms among newspaper employees using video display terminals (VDTs).

In contrast, other studies have reported that neck and shoulder muscular pain is more common among females than males, both in the general population and among industrial workers.

An important study noted that significant gender differences in work posture were related to stature and concluded that the lack of workplace accommodation to the range of workers' height and reach may, in part, account for the apparent gender differences. Also, the fact that more women are employed in hand-intensive jobs and industries may account for the greater number of reported work-related MSDs among women. Another study reported that men were more likely to develop DeQuervain's disease* than women; they attributed this to more frequent use of hand tools.

*DeQuervain's Disease is an irritation and swelling of the sheath or tunnel that surrounds the thumb tendons as they pass from the wrist to the thumb.

Work Station Criteria (Continued)

Physical Activity

loggers

The relationship of physical activity and MSDs is more complicated than just "cause and effect." Physical activity may cause injury. However, the lack of physical activity may increase susceptibility to injury. A lack of physical activity after injury may increase the risk of further injury.

We can define "fitness" for most physical activities as combinations 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. However, the most fit group had the most severe back injuries.

When physical fitness is examined as a risk factor for MSDs, results are mixed. One study reported that only 7% of absenteeism could be explained by age, sex, and physical fitness. On the other hand, another study found that physical capacity was related to musculoskeletal fitness.

Although physical fitness and activity are generally accepted as ways of reducing work-related MSDs, the present epidemiologic literature does not give such a clear indication. However, there is clear evidence that stretching exercises do have a positive effect on the reduction of MSDs.

Check out this short audio clip by Dan Clark of the theSafetyBrief.com that gives a good introduction about the importance taking stretch breaks during work.

Work Station Criteria (Continued)

Strength

climbers

Some epidemiologic support exists for the relationship between back injury and a mismatch of physical strength and job tasks. One important study found a sharp increase in back injury rates in subjects performing jobs requiring strength that was greater or equal to their isometric strength-test values. The risk was three times greater in the weaker subjects.

A second study evaluated the risk of back injuries and strength and found the risk to be three times greater in the weaker subjects. They found that job matching based on strength criteria appeared to be beneficial.

In another study, it was found that reduced strength of back flexor muscles was a consistent predictor of recurrent or persistent back pain, but this association was not found for first time occurrence of back pain.

spine

Strength vs. Energy of Work

Strength is important, but not necessarily the key. "Heavy work" stresses the heart and lungs which may result in rapid fatigue - general or localized. 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.

There are four factors that increase forces compressing the L5/S1 vertebrae together.

  • Weight on the upper body
  • Deviation from a correct postural stance
  • Weight of the load
  • Pull of the lower back muscles

Anthropometry

anthro

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. This information is then used by designers to engineer tools, equipment, furniture and workstations for maximum efficiency for each individual worker.

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 MSDs, especially Carpal Tunnel Syndrome (CTS) and lumbar disc herniation.

The relationship of CTS and BMI has been suggested to relate to increased fatty tissue within the carpal canal or to increased hydrostatic pressure throughout the carpal canal in obese persons compared with slender persons. Carpal tunnel canal size and wrist size has been suggested as a risk factor for CTS, however, some studies have linked both small and large canal areas to CTS.

Some studies have reported that people with back pain are usually taller than those without it. A Finnish population study found that height was a significant predictor of herniated lumbar disc in both sexes, but a moderately increased BMI was predictive only in men.

Another study of workers in 11 factories found that short stature was significantly associated with pain in the neck and shoulder, but not in the back, forearm, hand, or wrist. However, in two other studies involving thousands of workers, height was not a factor for neck, shoulder, hand, or wrist MSDs.

Anthropometric data are conflicting, but in general indicate that there is no strong correlation between stature, body weight, body build and low back pain. Obesity seems to play a small but significant role in the occurrence of CTS.

So there you have it. Not everything you need to know, but it's a start. The only task left is the module quiz, so let's get to it.

Ergonomic Risk Factors

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Which of the following is not described in the text as a critical component of the loads imposed on tissues, which can lead to cumulative trauma disorders CTDs as well as other musculoskeletal disorders?

2. The musculoskeletal system is made up of all of the following parts, except _____.

3. By the age _____, most people have had their first episode of back pain _____.

4. The age groups with the highest rates of compensable back pain and strains are the _____ age group for men, and _____ age group for women.

5. It is clear that differences seen with some MSDs are due to physiological differences rather than differences in exposure.

6. One important study concluded that the lack of workplace accommodation to the range of workers' height and reach may, in part, account for the apparent gender differences.

7. When physical fitness is examined as a risk factor for MSDs, results are mixed. One study reported that _____ of absenteeism could be explained by age, sex, and physical fitness.

8. When physical fitness is examined as a risk factor for MSDs, results are clear that it is a way of reducing work-related MSDs.

9. Demanding repetitive or static muscular work requires energy, not necessarily strength.

10. Anthropometric data are conflicting, but in general indicate that there is strong correlation between stature, body weight, body build and low back pain.


Have a great day!

Important! You will receive an "error" message unless all questions are answered.