The Effect of Exercise on Lipid Metabolism in Men and Women

Lipoprotein abnormalities constitute a major risk for development of cardiovascular disease. These substances, which are comprised of various lipids and proteins (apoproteins), are influenced by specific enzymes which eject their concentrations. It has been demonstrated that elevated total cholesterol and LDL cholesterol are directly associated with the development of coronary artery disease, whereas HDL cholesterol has an inverse relationship with coronary heart disease (CHD). Although more controversial, triglycerides may also be directly associated with coronary atherosclerosis. Favourable changes in lipid levels have been shown to reduce coronary mortality. Exercise may constitute a non-pharmacological approach to lipoprotein therapy. Many exogenous factors also influence lipoprotein concentrations. Changes in diet, body composition, age, as well as medication and akohol usage may directly alter lipid levels. In addition, they can be artificially affected by the analytical method. The immediate effects of one to several bouts of physical activity appear to influence lipoprotein level A reduction in triglycerides has been shown afler physical exertion, especially among trained individuals and those with hypertriglyceridaemia. These acute changes may reflect the utilisation of both muscle and plasma triglycerides as fuels during exertion. After more prolonged training, changes in lipoproteins may also occur. However, since exercise is accompanied by many co-variables which also favourably alter these levels (e.g. lower percentage of body fat, dietary alterations), it is difficult to determine the direct effect of regular physical activity. Initial studies of exercise training’s ejects on total cholesterol did not differentiate changes in HDL and LDL cholesterol. Subsequent research has observed these specific cholesterol fractions. Consistant reduction in LDL cholesterol levels have not been convincingly demonstrated. Although HDL cholesterol has been shown to increase in certain studies, the response has been variable in other investigations. These latter responses may have been due to the fact that HDL cholesterol changes may be dependent on levels prior to conditioning. Assessment of HDL cholesterol subfractions (HDLL₂ and HDL₃), which could additionally impact on cardiovascular risk reduction, have shown favourable increases in HDL₂, but as yet these HDL moieties have not been adequately investigated. Reductions in triglyceride levels ajier training among those with elevated values and benecial apoprotein changes post-training have been reported, although few studies exist. Recent research suggests that improved lipid profiles after exercise may be due to alterations in lipoprotein enzyme activity. This area will be important in the future and offers promise for explaining the relationship of exercise and lipoprotein change, as well as the variability of response observed among individuals. Although most studies have considered aerobic training, other forms of exercise such as resistive or strength training, may also evoke favourable lipoprotein changes. Additionally, a preponderance of exercise and lipid research have concerned men. Women have generally shown a lowering of lipoprotein risk factor levels after training. Previously reported contrary data probably reflects women’s pre-exercise low risk lipid profiles. A reduction in coronary mortality has been associated with an active lifestyle. Likewise, an association between exercise and beneficial lipoprotein levels exists. Further prospective randomised studies of individuals with lipoprotein abnormalities, controlled for confounding variables, are necessary before the ejects of physical exertion and lipid metabolism are more clearly understood.