Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-007882, 2008 Nov; :1-153
Falls from heights are a major problem in both industry and general society when measured in terms of economic losses and human suffering. Given that most of these falls are believed to result from a loss of balance, appropriate strategies to address the problem of falls should focus on improving balance control. Existing research has identified a number of major extrinsic and intrinsic factors involved in the control of balance. Only recently has another intrinsic factor, localized muscle fatigue, been shown to influence balance control. Additional research is needed to further our understanding of how fatigue contributes to loss of balance and falls. To address these needs, three projects were completed using laboratory experiments and biomechanical modeling to investigate and mitigate the effects of localized muscle fatigue on balance control. An additional focus in these projects was on whether and to what extent the effects of fatigue might differ with aging, given the increasing age of the contemporary workforce. First, experiments were conducted to examine and quantify the effects of age and localized muscle fatigue on balance control and the ability to recover from a balance perturbation. Acute effects of fatigue on relatively static postural control differed depending on the fatigue location, with substantial effects evident at the ankle and low back. Such acute effects were only evident among younger participants (18-25 years), but these same participants exhibited higher rates of recovery following fatigue. Under more dynamics conditions, specifically when responding to an external perturbation, a fatigue-induced decrement in the ability to recovery balance was evident, and more so among older participants (55-65 years). These results indicate that certain occupational tasks (i.e. those that fatigue the back and ankle muscles) can compromise balance, and thereby increase the risk of falls, and provide guidance for future control measures. In addition, there may be situations in which older individuals are at a relatively high risk of fatigue-induced loss of balance and falls. Subjective reports of perceived stability corresponded to objective measures of postural control among both younger and older participants, and were similarly sensitive to fatigue-induced changes. This suggests the potential utility of such perceptual responses for exposure monitoring and interventions (the latter was formally evaluated, as below). Second, biomechanical models were developed to quantify balance control strategies in terms of joint torques and underlying control mechanisms, and to facilitate predictions of effects of localized fatigue and potential interventions. Age-related differences were found in the use of major muscle groups when maintaining static balance both before and after fatigue. Post-fatigue differences in postural strategy were suggested for older participants. These age differences suggest an adaptability of the postural control of older individuals in response to fatigue. Theory-based models were used to simulate balance behaviors, and provided evidence for age- and fatigue-related effects on underlying postural control mechanisms (e.g. weighting of sensory information, sensory noise, etc.). Such modeling offers directions for training programs. Third, the effectiveness of interventions aimed at reducing the adverse effects of fatigue on balance control was determined. Use of applied pressure at the ankle (analogous to ankle taping) was found to improve postural control in the presence of fatigue, particularly in certain individuals. Effects of load carriage were investigated, both experimentally and using a simulation model. Influences of both load magnitude and location were identified, and provide guidance for task design and evaluation. Further, the simulation model can be used to evaluate the effects of a diverse range of additional load carriage tasks on balance. Using perceived stability was found to be potentially beneficial in managing the deleterious effects of fatigue on balance. Balance-related influences of the auditory environment were also evaluated. Specifically, preliminary evidence was provided that the use of a static pure tone reduces the adverse effects of fatigue on balance, and moving conversation increases these effects. Such results have potential for use as practical interventions. Completion of these projects has provided new information concerning factors that can adversely affect balance control and contributed to the development of intervention strategies for fall prevention. In light of epidemiological evidence of high fall risks among older workers, and demographic trends toward an aging population and workforce, emphasis was also placed on understanding age-related changes in the effect of fatigue on balance control. Fatigue is common during physically demanding work, and the knowledge gained can thus be used to develop practical interventions aimed at improving balance and decreasing risks of falls when such work is performed.
Fall-protection; Humans; Men; Women; Muscle-function; Muscles; Musculoskeletal-system; Fatigue; Models; Age-groups; Posture; Age-factors; Accidents; Epidemiology; Physical-fitness; Physical-exercise; Physiological-effects; Physiological-fatigue; Physiological-function; Physiological-testing; Physical-reactions
Maury A. Nussbaum, Ph.D., Virginia Tech, 250 Durham Hall (0118), Blacksburg, VA 24061