Tomorrow, and tomorrow, and tomorrow,
Creeps in this petty pace from day to day,
To the last syllable of recorded time;
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Macbeth: Act V - Scene V
Repetitive motions are actions that involve a worker performing one action movement multiple times in the doing of a job. Digging with pickaxes, cutting lumber with a saw, hammering nails, and lifting boxes are all examples of repetitive motions. Even in air-conditioned environments, using a mouse, typing on a computer keyboard, using a digital stylus and even answering phones are examples of repetitive movements. Repetitive movements occur outside of occupational contexts as well - gym-goers repeat movements like pulling on cables or lifting loaded barbells. People at home need to cut food using repeated strokes of a knife or stir a pot using repeated turns of a ladle. Even when getting from place to place - walking is a repetitive movement, just like cycling, or moving the foot from the accelerator to the brake. A person’s body performs these movements, and so these movements can cause strain in a person’s body. Repetitive movements undertaken as part of work are of particular concern, as these movements are undertaken over the time of a worker’s shift, for a significant portion of their week. Agricultural pickers such as migrant, itinerant, or tourist workers are a classic example of this, being at increased risk for muscular strain due to a combination of repetitive motion, lifting, and carrying (Kelly et. al., 2017). Office workers are exposed to repetitive movements owing to the use of mice and keyboards as well as other assets in professional environments (Jensen et. al., 2002). In Australia, during the 2021-2022 period, more than 10,000 hospitalisations occurred as a consequence of overexertion, strenuous and repetitive movement, wherein the lower limbs, trunk, and upper limbs were most often injured, and the most common injury were soft-tissue injuries (Australian Institute of Health and Welfare (AIHW), 2023).
Injuries due to repetitive motion are not new. Ramazzini, who is to occupational medicine as Hypocrites is to medicine as a whole, described illnesses caused by violent and irregular motions, and unnatural postures of the body (Franco & Franco, 2001). As industries and work processes have matured as a consequence of research, technologisation, and automation due to the development of tools and mechanical aids, and as market competitiveness has driven the streamlining of work related tasks for efficiency, the contemporary worker is required to work in a manner that exposes them to a high degree of repetition in their daily tasks (Luopajärvi et. al., 1979). Repetitive work exposes a worker to orthopaedic, neurological, and psychological risk factors (Australian Safety and Compensation Council, 2006a). The latter of these is best discussed with respect to psychosocial safety and will be discussed elsewhere. It is common for musculoskeletal disorders and injuries to arise from cumulative exposure to one or more hazards over an extended period (Oakman et. al., 2019). This makes identification and diagnosis of musculoskeletal disorders that have arisen due to occupational overuse difficult (Palmer et. al., 2008) - the tendency is to datemark times of injury, and the consequence of this is misdiagnosis or worse, omission of the relevant workplace hazard, and then development of controls that are inappropriately targeted. This is further complicated by the fact that workers need to use their bodies outside of work as well - a worker is also a human and humans have human needs, such as sustenance, self-care, and entertainment to sustain their dignity, wellbeing, and fullness of life (Citation needed). In the 2015-2016 period, of the number of claims related serious work-related musculoskeletal disorders, only 4.4% were due to repetitive movement and low muscle loading. However, this low number must understandably be evaluated in the understanding that injury investigations may not control for demographic and extracurricular contributing factors.
Injuries due to repetitive strain are described as Repetitive Strain Inuries (RSI), Occupational Overuse Syndromes (OOS), Cumulative Trauma Disorders (CTD) and other terms (Wigley, 1933). Disorders arising from repetitive strain injuries include tendon-related disorders like tendonitis and tenosynovitis, muscular disorders such as myositis and myalgia, the entrapment of peripheral nerves which presents as syndromes such as carpal tunnel, and capsular disorders such as bursitis or synovitis. This again may contribute to the poor diagnostic resolution of these injuries from an occupational context owing to the potential contribution of factors outside the workplace. Occupational overuse injuries arise due to the cumulative effect of forces on human anatomical structures over time (Moore et. al., 1991). The result of this cumulative effect is magnified, owing to the fact that none of the body systems used in contemporary occupations were evolved to engage in those occupations - occupational movements are inherently un-natural (Kumar, 2001). The repetitive, prolonged, and forceful exposure of tissues to mechanical stressors results in their inflammation and degradation, resulting in injury (Yassi, 1997). The interesting thing to note is that recreational strength and conditioning and bodybuilding work on the same basis - the dosing of resistance applied to specific muscle groups across ranges of motion in sets and repetitions, and the arrangement of progression across a cycle of exercising and resting days is designed to optimise exposure to load and consequently physical conditioning. However, in an occupational context, the worker addresses the needs of the task five continuous days out of the week, with little opportunity to adjust the exposure dose, and little chance to mitigate the adverse biomechanical effect of stress exposure. In occupational overuse syndromes, exposure of body structures to mechanical stress and strain that exceeds the body’s ability to adapt and repair over time results in injury that seems to arise from no cause at all (Kumar, 1990). From a pathoanatomical perspective, the changes that occur as a consequence of repetitive strain depend on the histology of the tissue affected by that strain. In carpal tunnel, compressive loading of the median nerve is hypothesised to increase pressure within the carpal tunnel that occludes blood supply, and the subsequent anoxia results in oedema and inflammation (Barr & Barbe, 2002). Biopsy of tissues of patients with painful overuse syndrome reveals changes consistent with loss of type II muscle fibers and hypertrophy of type I muscle fibers (Dennet & Fry, 1998). Again, these are adaptational changes that have come about due to exposure to specific forces in specific doses. Changes have also been found in overused muscles where tissues show signs of oxygen depletion (Larsson, 1990; Larsson, 1999) and which may be further aggravated by changes in the function of nerves serving power to and conveying sensation from those muscles (Edwards, 1988). The broad themes common to occupational overuse injuries are increased and chronic inflammation, microdamage due to tension, compression, and shear, thickening of connective tissue, and inflammation of that connective tissue as well. Neuronal changes include fibrosis, swelling of the perineurium, and thinning of the nerve sheaths as well (Elliott et. al., 2009). These changes may reflect short-term or accelerated changes, and contribute to the experience of severe discomfort that may require a worker to change occupation if not appropriately managed, and which may cause significant expense for employers (Rempel et. al., 1992)
The interaction between different neural, muscular, and bony factors as a consequence of task demands is aptly illustrated in Figure 1
Figure 1
Conceptual Schematic for the Development of Work-Related Musculoskeletal Disorders
Note. Reproduced from Barr, A. E., & Barr M. F. (2002). Pathophysiological tissue changes associated with repetitive movement. Physical Therapy, 82(2) 173-87
While this goes some way to visually illustrating the cumulative and reinforcing effect of pathological, occupational, and individual factors in the expression of disease owing to occupational overuse injuries, the crucial deficit of this model is that clinical intervention can also address the task demands of the worker as part of a rehabilitative process. This model also does not examine the potential contributory effect of psychosocial hazards on demands and resources, though this is understandable given the scope of the research undertaken. This effect will be discussed in the future, and a more comprehensive model of this consideration is shown in Figure 2 below.
Figure 2
A composite, ergonomics model of work-related hazards for musculoskeletal disorders.
Note. Retrieved from Australian Safety and Compensation Council. (2006b). Research on the Prevention of Work-Related Musculoskeletal Disorders. Stage 1 - Literature Review.
The physical effects of injuries arising from repetitive strain are more insidious than the effect of injuries that come about due to discrete traumatic events. Because discomfort comes on slowly, repetitive strain injuries present with constellations of symptoms, some of which may be more or less prominent depending on the root cause. Pain is stereotypical of all repetitive strain disorders, and irritation to or involvement of a nerve trunk or root may produce numbness and tingling in the distribution of skin served by that nerve. Overuse injuries affecting multiple joints or the spine may present with stiffness, localised pain, and pain that changes with time of day and exertion. Irritation of a nerve close to the point at which it exits the spine will elicit pain in the distribution of skin and muscle innervated by that nerve.
Injuries arising from repetitive strain can be mitigated by reducing the degree of repetition, increasing the amount of break time available, decreasing the force required, and changing the task. The Hierarchy of Controls recommends removal of the source of risk as the most effective form of risk control (Comcare, n.d.), while engineering safety and substitution are used where elimination is not possible (Safe Work Australia (SWA), 2018). In this case, engineering safety and substitution may both be achieved by automation of the task. Nailguns can reduce the need to hammer. Table saws reduce the need to use a bladed saw to cut wood or appropriate material. Electric whiskers and blenders reduce the need for cooks to blend food, and sewing machines minimise the need to produce stitch types by hand. However, changes to work duties may introduce other risks as a consequence of substitution - a nailgun has tool kickback and needs to be handled carefully. An electric blender is a trapping hazard, and a sewing machine produces noise and vibration from its operation. The rotation of workers through different tasks also needs to be considered, as if workers are rotated through work that involves similar movements, postures, and forces, their risk profile remains the same regardless of what their duties involve (WorkSafe Victoria, 2022), and workers may be more likely to report hazards while using equipment than when not (Harrell, 1990) which may affect reporting of hazards in white-collar job roles. It is necessary to observe workers undertaking repetitive tasks and consult with them to ensure that an accurate assessment of risk, exertion, and repetition is made (NOHSC, 1994; NOHSC, 1996; Madeleine et. al., 2003). More broadly, task analysis that examines details including shift times, cycle times, frequency and duration, as well as risk points can illustrate potential points of improvement at the workplace level. Additional contributory factors such as awkward postures, contact stress from material handlings, whole-body vibration and exposure to cold temperatures should also be considered, wherein a worker such as an abattoir worker in a refrigerated environment may be particularly at risk (Williams & Westmorland, 1994). Workplace environments, task repetition and homogeneity, decreased time for rest, and an increase in work demands have also been identified as major contributing elements in the development of repetitive strain injuries (Iqbal & Alghadir, 2017). The difficulty in preventing repetitive strain injuries in an occupational context is that risk management interventions undertaken in the workplace can be invalidated by worker habits and activities outside of work. A worker experiencing occupational strain from overhead lifting may again load their arms if they are a recreational tennis or basketball player. A worker whose hands are strained from typing and mousing may experience additional strain if they play a musical instrument, enjoy knitting, or play video games recreationally or professionally. Management of occupational repetitive use injuries is difficult because to manage those injuries is to have to account for the worker as an independent entity, which can be challenging when designing interventions for sustainability and ease of implementation. Indeed, the effect of occupationally induced overuse syndromes can cause stress as a consequence of difficulty engaging in recreation, which may in turn magnify the effect of experienced symptoms (Nicholas et. al., 2011). Effective control of repetitive forces on workers requires intervention from the design level - the arrangement of tasks and workspaces in such a way that repetition is minimised or identified early and proactive steps taken to minimise a worker’s exposure to sustained forces.
Human technological advancement has improved the quality and length of human lifespans. However, despite changes in how humans go about living their lives and working, a human at work is still a human body in motion, meeting the demands of tasks that are so far advanced in development as to be alien to an anatomy which has remained functionally similar to those ancients who built the Towers of Tell Qaramel. The human body has a head that can see, hear, smell, taste, speak and sing, arms that can embrace and hold our loved ones, legs that can run and dance, hands that can play instruments, and a lifespan in which to engage with these capacities. However, owing to the construction of the contemporary labour market and the systemic descendants of that market, we are condemned to sublimate the incredible wonder of our anatomy and its constituent capabilities to the undertaking of piecework cognitive and concrete tasks until such time as we retire and are given the freedom to exercise what capacities are left, or until we die. Occupational overuse injuries are difficult to diagnose, difficult to treat, and difficult to mitigate proactively or in parallel with their exposure profile, but effective management of overuse injuries is reflective of the application of best principles of best management of worker safety as a whole, which is important for the simple point that human capital precedes economic capital.
None of this information constitutes medical, legal, occupational health and safety, best guidance, standard, or other guidance, instruction, or prescription.
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References
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