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The Work Injury Consulting Practice
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II. Repetitive task manufacturing jobs design strategies:

As stated earlier in this text,repetitive motion, per se, is not the truly critical issue. The issue to consider first is thesustained posturedemands required of repetitive motion job tasks. One must usually maintain a sustained posture, such as sitting or standing at the work station, to carry out repetitive motion work. It is this sustained posture component that is usually the most critical issue. And sustained posture stresses are often easier to manage than are attempts to reduce repetitive motion demands. Sustained posture requires sustained muscle contraction, sustained tendon tension, and sustained joint compression. This creates mechanical tissue pressures that can readily exceed circulatory perfusion pressures, thus depriving these working tissues of their nutrient pathway. This forces anaerobic metabolism, which rapidly burns up oxygen and glucose stores while creating large amounts of metabolic wastes. These wastes cause irritation to the tissues, resulting eventually in inflammation. This is, thus, the mechanical and chemical model ofcumulative trauma disorder(CTD) as anutrient pathway disorder. Repeated movementsare not innocent in this process. But we have traditionally assumed it to be a friction wear damage model. This is likely not the true mechanism of damage of repetitive motion. What is more likely is yet another process of interruption of nutrient pathway. This time it is a process of repeated muscle contraction, tendon tension, and joint compression. But what is significant is that when this is a repeated contraction, there isdiminished relaxationof the contractile tissues between each cycle of contraction; the greater the frequency of contraction, the less the level of relaxation between each contraction. The result is a sustained and often growing level of background tension during the repetitive motion process. This, again, produces an interruption ofnutrient pathway. If we assume this to be the mechanism of CTD pathogenesis, we can see several possible avenues for prevention intervention. It is very difficult to reduce repetitive motion in today's workplace. Production needs simply will not allow this in most cases. But we can find several acceptable methods ofboosting tissue perfusionwithout reducing production, perhaps even increasing production due to enhanced performance and reduced fatigue of the working body. This is where we begin to consider frequent but brief stretching of key tissues affected by posture and motion demands, job task rotation or sit-stand options to reduce time exposure to otherwise relentless stresses to working tissues as adjuncts or alternatives to often expensive ergonomic design changes. We always start our intervention problem-solving with trying to correct fixable ergonomic design stresses. These can alleviate critical stresses. But ergonomic alternatives are often elusive and sometimes expensive. So we always keep in mind stretches, rotation, sit-stand options, and self-care of the working body as alternative prevention strategies. Stretching briefly and often can result in a relaxation of working tissues, allowing restoration of perfusion to replenish nutrients, flush wastes, and deliver materials needed for tissue repair. Task rotation and frequently switching between sitting and standing can shift workloads among a larger population of working tissues to disperse workloads and provide periods of reduced tissue loads for restoration of perfusion. Click Here to Return to Product Page