Impact of control mechanisms and tissue morphology on upper extremity loading

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Work-related disorders cost Canadians billions of dollars every year. There is a great need to fully understand the mechanisms by which tissues of the upper extremity (shoulder, arm, and hand) become overloaded at work. What makes these mechanisms interesting and complex is that they develop over a long period of time, making it difficult to pinpoint what caused the damage. These disorders involve muscle, connective tissue (e.g. tennis elbow, tendinitis), and peripheral nerves (e.g. carpal tunnel syndrome). Before understanding these disorders and making jobs safer for workers, it is essential to characterize the mechanisms underlying how healthy tissues respond to a range of loading conditions. My research program that evaluates the response of healthy tissues to a variety of postures, loads, interfering tasks, and fatigue (localized and central), as well as aging. We must also understand the complex interactions between anatomy and the control of movement. Studies indicate that loads, postures and motion are highly linked to overloading tissues which may lead to tissue damage. However, the majority of studies are correlative and do not address why and how these tissues are overloaded. We have a fundamental need to understand how tissues react to the plethora of conditions, at work and otherwise. Without this knowledge, we may cause the unwanted effect of over stressing the body. My research program methodically investigates the effects of muscular loading by monitoring arm movement, muscle activity and their interactions using computer-based modeling. We use magnetic resonance imaging (MRI) and ultrasound to examine structural changes in the tissues of the wrist in different postures during pinching actions. These studies determine mechanics of nerve compression at the wrist. We also examine muscle activation patterns (timing and magnitude) of the shoulder, arm and hand to determine how muscles work to create movement in specific tasks. Adding complexity to tasks can alter how someone performs the task. In particular, adding a task that competes with the main task, such as a grip or a mentally taxing task, may be detrimental to the outcome. Compensatory strategies to control the hand, arm and shoulder muscles may indicate which individuals are susceptible to greater individual muscle loading, fatigue and injury. Further, by performing studies comparing muscles fresh versus fatigued, we can determine the way people deal with tiring stereotypical movements like on an assembly line. A major part of this research program is to develop and improve our computer models to predict forces inside the arm and hand. By combining muscle activity and anatomical information in a computer model, we can test theories on how disorders develop and how to prevent them as well as ask "what would happen if ...?" questions that otherwise could not be answered ethically in living beings.