Exercise combined with dietary intervention continues to hold the best promise for combating the obesity epidemic. Brisk walking is a recommended and popular form of exercise but weight bearing exercise may be the source of the biomechanical loads that increase the risk of musculoskeletal injury and link obesity and large joint (e.g. knee) osteoarthritis (OA). Thus, prescribing brisk walking as exercise for treating obesity may be biomechanically unsound. However, remarkably little is known about how obesity affects the biomechanical loads involved in walking. The existing walking biomechanics data base does not apply to the 60+% of American adults who are overweight or obese nor to uphill or downhill walking. The long term goal of this research is to derive walking exercise prescriptions for obese adults that minimize lower extremity biomechanical loads while optimizing caloric expenditure and cardiovascular stimulus. Specific Aim 1: Determine how obesity affects the biomechanics of walking. We hypothesize that obesity increases lower extremity joint loads but that moderate inclines combined with decreased walking speed reduce these loads while walking down moderate declines increases lower extremity joint loads. To test these hypotheses, the musculoskeletal biomechanics will be measured across speed on the level, three inclines and one moderate decline using our inclinable, dual-belt force measuring treadmill. Obese and normal weight control subjects of both genders will be studied. Specific Aim 2: Develop more sound guidelines for prescribing walking exercise for obese adults. We hypothesize that for obese adults, slow walking up a moderate incline minimizes knee joint loads while optimizing caloric expenditure and cardiovascular stimulus. To test this hypothesis, we will combine our biomechanical results from Specific Aim 1 with measurements of the metabolic cost of walking and maximal oxygen consumption rates of obese and normal weight adults. We will be able to identify speed and incline combinations that achieve the recommended sustainable moderate aerobic intensity (55-70% of maximal oxygen uptake, VO2max) with the lowest biomechanical loads. The benefits of this research will be more informed, safer and more effective prescriptions of walking as exercise for weight management and cardiovascular health. The walking regimens that we determine should be safer in the shorter term (reduced rates of acute injuries) and longer term (reduced risk of OA). PUBLIC HEALTH RELEVANCE: Obesity is a chief contributor to preventable deaths in the United States and poses a major health challenge associated with increased morbidity and mortality. Brisk walking is a recommended and popular form of exercise for obesity prevention and treatment but may be the source of the biomechanical loads that increase the risk of musculoskeletal injury and link obesity and large joint (e.g. knee) osteoarthritis. The benefits of this research will be more informed, safer and more effective prescriptions of walking as exercise for weight management and cardiovascular health.