Relationship between Physical Activity and Health
Crosssectional epidemiologie studies and controlled, experimental investigations12 have demonstrated that physically active adults, as contrasted with their sedentary counterparts, tend to develop and maintain higher levels of physical fitness. Epidemiologie research has demonstrated protective effects of varying strength between physical activity and risk for several chronic diseases, including coronary heart disease(CHD),hypertension,non-insulin-dependent diabetes mellitus,osteoporosis,colon cancer,and anxiety and depression.
Other epidemiologie studies have shown that low levels of habitual physical activity and low levels of physical fitness are associated with markedly increased all-cause mortality rates.
A midlife increase in physical activity is associated with a decreased risk of mortality.It has been estimated that as many as 250 000 deaths per year in the United States, approximately 12% of the total, are attributable to a lack of regular physical activity.
The conclusions of these epidemiologie studies are supported by experimental studies showing that exercise training improves CHD risk factors and other health-related factors, including blood lipid profile,resting blood pressure in borderline hypertensives,body composition,glucose tolerance and insulin sensitivity, bone density,immune function,and psychological function.
Epidemiologie criteria used to establish causal relationships can be applied to the association between physical activity and CHD.The following principles of causality appear to have been met: Consistency: The association of physical in activity and risk of CHD is observed in a number ofsettings and populations, with the better designed studies showing the strongest associations.
Strength: The relative risk ofCHD associated with physical inactivity ranges from 1.5 to 2.4, an increase in risk comparable with that observed for hypercholesterolemia, hypertension, and cigarette smoking.
Temporal sequencing: The observation of physical inactivity predates the diagnosis of CHD. Dose response: Most studies demonstrate that the risk of CHD increases as physical activity decreases.
Plausibility and coherence: Physical activity reduces the risk of CHD through a number of physiological and metabolic mechanisms. These include the potential for increasing the level of high-density lipoprotein cholesterol; reducing serum triglycéride levels; reducing blood pressure; enhancing fibrinolysis and altering platelet function, thereby reducing the risk of acute thrombosis; enhancing glucose tolerance and insulin sensitivity; and reducing the sensitivity of the myocardium to the effects of catecholamines, thereby reducing the risk of ventricular arrhythmias.