Matt Culloty, Ergonomist and Safety Consultant, outlines the growing recognition prolonged postures as a Musculoskeletal hazard.
Muscle fatigue results when a muscle group can no longer sustain the force required for an activity (noting that work done = force x distance). It is easy to understand the link when we go for a run or do manual labour and see how our body is ‘working’. We subsequently find it increasingly difficult to maintain that pace or level of energy output after sustained exertion.
This fatigue is usually down to the dynamic movements of our muscles. There is however a less obvious form of muscle work that causes muscle fatigue and subsequent musculoskeletal injuries (MSI’s). This fatigue often results from prolonged postures (standing, sitting, awkward postures) where the body or group of muscles requires minimal movement for extended periods of time. This is called static muscle contraction, although the word static suggests no movement, the muscles are still working to maintain that posture or sustain a low force task for long durations.
For example, outstretch your arm and hold it there, you are not holding any load except the weight of your arm’s muscle and bones, nor are you doing any dynamic movements. How long can you maintain that posture? This will vary on your strength, stamina etc. but inevitably your muscles will tire, and you will be forced to lower your arm. Simply put this is because your upper limb muscles are working to maintain that posture while using up energy and with sustained muscle contraction this can restrict blood flow which normally provides oxygen to the muscles and inhibits the mechanism for nutrients and waste products to be transported.
Some examples where this can occur in the work place are, a seated office workstation with people leaning/hunched over their workstation, this places added strain on the lower back, an incorrect seat or screen height which can result in raised shoulders or deviated head/neck postures. Or it can be localised to maintaining a grip hold on a hand tool because the process dictates these postures with limited rest/recovery periods.
Standing postures such as using the standing mode only in a sit/stand desk or working at an assembly/inspection workstation that is a static station. This can place additional strain on the lower back and limbs over time. What increases the risk for MSI can be the duration (time spent in that posture), type/degree of deviated postures (what degree away from neutral is the posture) and frequency (how often that posture needs to be adopted).
So, taking account of the postural issues outlined above, some tips to reduce these MSI risks in any type of work include:
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