The Surgeon General’s report concluded that physical activity is causally related to health outcomes. Numerous studies were analyzed to determine ( a) the The majority of the studies controlled for important confounding factors that might have biased the results, such as age, body weight, smoking, blood pressure, blood lipid levels, alcohol consumption, and disease status. Most studies reviewed in the Surgeon General’s 1996 report were cohort studies that is, they assessed whether an association existed between some baseline level of physical activity or fitness and the development of specific health outcomes. Instead, the effect of physical activity on intermediate outcomes, such as fitness or coronary heart disease risk factors, has been evaluated. The high cost and feasibility constraints of large-scale clinical trials have thus far prohibited such designs with major morbidity or mortality as health outcomes. Often considered the gold standard of studies, clinical trials are extremely expensive and time-consuming and require that every precaution be taken to protect the study participants. Cross-sectional studies assess the association between physical activity and disease at the same point in time thus they offer limited ability to draw causal inferences between the two variables.Ĭlinical trials, in comparison, assess the relationship between health outcomes and physical activity by experimentally altering the activity patterns, levels, and intensities within a relatively controlled environment, such as in a laboratory or an exercise program (DHHS 1996). Their previous level of physical activity is compared with that of a control group that does not have the disease or health condition of interest. In contrast, case-control studies start with a group of individuals (the case group) with a specific disease or health condition of interest, who are then asked to recall their previous level and intensity of physical activity. Cohort studies follow a population to observe how physical activity levels or habits affect the incidence of disease or mortality. Epidemiologic studies include cohort, case-control, and cross-sectional research designed to estimate the relative magnitude or strength of an association between physical activity or cardiorespiratory fitness levels and a specific health outcome. Viduals who develop specific diseases or health conditions and those who do not. Total activity levels-purposeful physical activity or exercise, as well as utilitarian physical activity that occurs in the home, at work, and in travel-are of interest. Health is broadly defined as a “state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity” (WHO 1946). This study uses the broadest possible definition of physical activity because all types of such activity contribute to health. For example, achieving a certain level of cardiorespiratory fitness-a health-related fitness goal-requires an increase in cardiorespiratory endurance that can either help reduce the risk of cardiovascular disease or improve the life and overall health of a person who already has the disease.Įxercise is considered a subcategory of physical activity and has been defined as “physical activity that is planned, structured, repetitive, and purposive in the sense that improvement or maintenance of one or more components of physical fitness is the objective” (Caspersen et al. Depending on the individual’s performance or health goal, specific attributes of physical fitness become more important (Caspersen et al. Related fitness or health-related fitness (DHHS 1996).
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