Physical Risk Factors
Awkward Postures
Body postures determine which joints and muscles are used in an activity and the amount of force or stresses that are generated or tolerated.
For example, more stress is placed on the spinal discs when lifting, lowering, or handling objects with the back bent or twisted, compared with when the back is straight. Manipulative or other tasks requiring repeated or sustained bending or twisting of the wrists, knees, hips, or shoulders also impose increased stresses on these joints. Activities requiring frequent or prolonged work over shoulder height can be particularly stressful.
Forceful Exertions (Including Lifting, Pushing, and Pulling)
Tasks that require forceful exertions place higher loads on the muscles, tendons, ligaments, and joints. Increasing force means increasing body demands such as greater muscle exertion along with other physiological changes necessary to sustain an increased effort. Prolonged or recurrent experiences of this type can give rise to not only feelings of fatigue but may also lead to musculoskeletal problems when there is inadequate time for rest or recovery.
Force requirements may increase with:
- increased weight of a load handled or lifted
- increased bulkiness of the load handled or lifted
- use of an awkward posture
- the speeding up of movements
- increased slipperiness of the objects handled (requiring increased grip force)
- the presence of vibration (e.g., localized vibration from power hand tools leads to use of an increased grip force)
- use of the index finger and thumb to forcefully grip an object (i.e., a pinch grip compared with gripping the object with your whole hand)
- use of small or narrow tool handles that lessen grip capacity
Repetitive Motions
If motions are repeated frequently (e.g., every few seconds) and for prolonged periods such as an 8-hour shift, fatigue and muscle-tendon strain can accumulate. Tendons and muscles can often recover from the effects of stretching or forceful exertions if sufficient time is allotted between exertions. Effects of repetitive motions from performing the same work activities are increased when awkward postures and forceful exertions are involved. Repetitive actions as a risk factor can also depend on the body area and specific act being performed.
Knowledge Check Choose the best answer for the question.
3-2. Which of the choices below increases force requirements?
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