Introduction to Ergonomics

Oregon OSHA Course #201

This material is for training purposes only. Its purpose is to inform Oregon employers of best practices in occupational safety and health and general Oregon OSHA compliance requirements. This material is not a substitute for any provision of the Oregon Safety Employment Act or any standards issued by Oregon OSHA. For more information on this online course and other OR-OSHA online training, visit the Online Course Catalog.

MODULE THREE: RISK FACTORS INHERENT IN THE TASK

Forcefulness is the amount of physical effort required by the person to do a task and/or maintain control of tools and equipment. The effort depends on the type of grip, object weight, object dimensions, body posture, type of activity, slipperiness of object, temperature, pinching, vibration, duration of the task and number of repetitions. Using the body to move another object can result in forces being exerted on internal body tissues that can result in compression of the spine, tension within a muscle/tendon groups. Examples of work activities that exert force on the body include lifting, lowering, pushing, pulling, pinching, pounding, hitting, and jumping.

Contact Trauma. When any part of your body presses against an external object, the resulting sustained force may cause too much mechanical stress on tissues. It is also possible for excessive mechanical stress to be produced from the impact shock of an object against a part of the body.

• The Pinch Grip which depends on the fingers to exert the force and manipulate the object. This grip strategy requires much greater muscle strength so it is more likely going to cause an injury.
  
  
• The Power Grip uses the muscles of the entire hand to apply force and manipulate objects. Consequently, it's the most effective, and safest, grip to use.

Gloves. Have you ever worn thick leather gloves while trying to accomplish some kind of intricate manipulation of small objects? Try it: you will be frustrated. Whenever you wear gloves, more grip force is required to a particular task. With the need for more force, increased risk of injury is occurs. Bulky clothes. Wearing bulky clothes, like heavy rain gear or protective clothing for removing hazardous waste, will increase the effort required by muscles to do work. Any time you increase the force necessary to complete a task, risk of injury also increases.

Vibration When handling vibrating tools for a prolonged duration, vascular insufficiency in the hand and fingers which can also result in interference with sensory receptor feedback. If a worker can't "feel" the grip properly, he or she may compensate by applying more force than is necessary to hold and handle an object. Segmental vibration has also been linked to carpal tunnel syndrome.

Repetition is a measure of how frequently we complete the same motion or exertion during a task. The severity of risk depends on the frequency of repetition, speed of the movement or action, the number of muscles groups involved, and the required force. Repetitiveness is influenced by machine or line pacing, incentive programs, piece work and unrealistic deadlines. For instance, an experienced worker packing apples (piece work) may complete many more similar exertions or movements than a new worker. Unfortunately, he or she may be performing as such a rapid rate that they may be developing a CTD. Repetition, alone, is not an accurate predictor of injury. Other factors, like force, posture, duration, and recovery time must be considered.

Duration is a measure of length of time of exposure to a risk factor. Of course, the assumption is that the longer the duration of exposure, the greater the risk of injury. Duration may be measured in seconds, minutes, hours, days, weeks, months, and even years. As with most individual risk factors, duration must be considered along with other person, task, and environmental risk factors such as the physical conditioning of the worker, posture, force, weight, temperature, stress, etc.

Posture is the position of the body while performing work activities. Awkward posture is a deviation from the ideal working posture of arms at the side of the torso, elbows bent, with the wrists straight. Awkward postures typically include reaching behind, twisting, working overhead, kneeling, forward or backward bending, and squatting. If the posture is awkward during work, there is an increased risk for injury. The more the joint departs from the neutral position, the greater the likelihood of injury.

• Wrist flexion or extension which occurs regularly is associated with a greater risk of carpal tunnel syndrome.
• Ulnar deviation of the wrist of greater than 20 degrees increases the risk of pain and other disease.
• Shoulder abduction or flexion is greater than 60 degrees for more than one hour a day increases the risk of acute neck and shoulder pain.
• Hands working at or above shoulder level can result in increased risk of tendinitis and various shoulder disease.
• The greater the angle of flexion of the neck, the more quickly potentially severe neck and shoulder pain results.
• Bending at the lower back while working increases the likelihood of low back disorders.

• The angle between the upper arm and the forearm should be 70 to 135 degrees.
• The angle between the upper and lower leg should be 60 to 100 degrees.
• The angle between the torso and the thigh should be 90 to at least 100 degrees.
• The feet should be placed flat on the floor.

• The work surface should be 2 - 4 inches below elbow height for precision work.
• The work surface should be 4 - 6 inches below elbow height for if lifting light weights and working with bins, tools and other materials.
• The work surface should be 6 - 16 inches below elbow height if lifting heavy weights.

Twisting in the middle of a lift amplifies forces on the lower back. Imagine placing a tomato between the palms of your hands and applying direct pressure. It might take a great deal of force to burst the tomato. However, give the motion a twist while applying the pressure, and it will take far less pressure to burst the tomato. Twisting while lifting, pushing, pulling, lowering, or raising may have the same effect on the back. Consequently, if twisting while taking any of these actions exposes the back to much greater risk of injury.

Angular velocity is nothing more than the speed at which the body part moves. Acceleration is the rate of change of the speed at which the body part moves. For example, a drummer's hand/wrist may move very rapidly back and forth while drumming. The faster that back and forth motion occurs, the greater the risk of injury. Other factors like the weight of the object being moved, will also increase risk.

Work requiring heavy physical exertion places a greater demand on the body's cardiovascular system to provide the necessary oxygen and metabolites to muscle tissue. If a muscle group's demand for metabolites and oxygen cannot be met, that muscle group will become fatigued, increasing the risk of injury. When the muscle is tired and sore, it's fatigued, and injury may more likely occur. If the entire body becomes fatigued, an actual cardiovascular failure may occur.

MODULE Review Quiz

21. The amount of effort in performing a task depends on a number of factors. Which of the factors below is not mentioned in the text?

a. Type of grip
b. Object weight
c. Object dimensions
d. Fatigue

22. According to the Joyce Institute, compressive forces on the L5/S1 exceeding 550 lbs. causes _______ times the injuries than forces of less than 550 lbs.

a. 2
b. 4
c. 6
d. 8

23. According to the text, all of the following are common locations of injury due to exerting excessive force, except:

a. neck/shoulder
b. foot/ankle
c. upper back
d. wrist/hand

24. What condition exists when any part of your body presses against an external object and the resulting sustained force has caused too much mechanical stress on tissues?

a. Mechanical trauma
b. Recovery trauma
c. Force trauma
d. Contact trauma

25. This grip strategy to manipulate objects requires much greater muscle strength so it is more likely going to cause an injury:

a. pinch grip
b. power grip
c. sustained grip
d. intermittent grip

26. This form of exertion combines force, posture, and duration to create a condition that quickly fatigues our muscles which increases the chances of acquiring a cumulative trauma disorder (CTD):

a. intermittent exertion
b. repetitive exertion
c. static exertion
d. forceful exertion

27. If a worker can't "feel" the grip properly, he or she may compensate by applying more force than is necessary to hold and handle an object:

a. True
b. False

28. This term describes a measure of the rest (or low stress activity) period available to the muscle group between similar exertions:

a. rest period
b. recovery time
c. degree of recovery
d. muscle group rest time

29. According to the text, awkward postures typically include all of the following, except:

a. squatting
b. working overhead
c. bending
d. standing

30. _____________ is nothing more than the speed at which the body part moves and ____________ is the rate of change of the speed at which the body part moves:

a. angular velocity, acceleration
b. acceleration, angular velocity
c. angular acceleration, velocity
d. velocity, angular acceleration