Force alone is not a strong risk factor for WMSD, but in concert with other factors may lead to injury. Intuitively, greater force equals more muscular effort, and consequently, a longer time is needed to recover between tasks. It follows that more forceful movements cuase muscles to develop fatigue much faster.
Exerting force in certain hand positions can magnify any inherent risk. The weight of the tools and objects that the worker is required to manipulate as well as their placement in relation to the worker's body all impact the overall force the worker must generate to complete a task. For example, the required forces are magnified when leaning forward to perform work away from the body because body weight inherently poses a significant load. Furthermore, tools that force the wrist, elbow and shoulder into non-neutral positions substantially increase the force required. For example, working with the wrist bent impacts how strong the power grip is. A wrist positioned in just 30 degrees of flexion can decrease grip strength by up to 60%1. Thus, non-neutral wrist postures cause muscles to be less efficient, resulting in greater efforts and quicker fatigue onset.Lastly, dull tools can dramatically increase the operating force, making tool maintenance especially important in the prevention of WMSD.
1Bhardwaj P, Nayak S, Kiswar A, Sabapathy SR. Effect of static wrist position on grip strength. Indian Journal of Plastic Surgery. 2011:44(1): 55–58.
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