Just 30 years ago, the biggest killer in Hong Kong was infectious disease. Today, coronary heart disease claims the most lives. The risk factors for heart disease include hypertension, physical inactivity, diabetes (type II), high cholesterol, high blood pressure and obesity. Of these factors, physical inactivity is the most prevalent. Research shows that when people do little or no physical activity they run a risk of developing one or several of the risk factors for heart disease. And in Hong Kong, a decrease in physical activity has coincided with an increase in heart disease. So how does exercise help prevent these risk factors? One way is that when you exercise you reduce the amount of activity in the sympathetic nervous system. This reduces the hormone (norepinephrine) that stops the resistance of insulin which controls body fat levels. The pancreas produces insulin, a hormone that moves glucose into muscle cells. With type II diabetes (non-insulin dependent), the pancreas produces enough insulin, but the cells don't respond to the insulin. This results in a build-up of glucose in the blood. The kidneys then remove the glucose leaving little fuel to power the body. Weight loss and exercise improves metabolism by increasing insulin sensitivity. Researchers have demonstrated that by improving aerobic capacity, glucose uptake is improved. This is due to increased blood flow which allows tissue to be more exposed to insulin and glucose. Other studies have found that weightlifting improves insulin action because it increases muscle mass, the largest tissue sensitive to insulin. Physical activity also provides protection against cardiovascular disease to people with high blood pressure. A study carried out by the Cooper Clinic in Dallas, Texas, found high levels of cardiovascular fitness protect men diagnosed with hypertension against cardiovascular disease. Experts don't consider cholesterol a health risk until there is too much of it. Excess cholesterol forms a thick and hard plaque along the walls of the arteries leading to the heart and brain. This plaque can lead to a heart attack or stroke. It's also considered a problem if the ratio of low-density lipoproteins (LDL) to high-density lipoproteins (HDL) is too low. Evidence shows regular exercise has beneficial effects on the HDL cholesterol levels. Exercise also keeps weight down. Losing excess weight and regular exercise help to maintain a good cholesterol level, including total cholesterol and may help improve HDL/LDL ratios. Physical inactivity is common in Hong Kong with more than half the adult population sedentary or not active. A survey by the Department of Health in 1999 showed only 51 per cent of men and 47 per cent of women between the ages of 18 and 64 participated in some form of exercise in the prior month. According to the Department of Health statistics, heart disease, including hypertensive heart disease, was the second leading cause of death in 1999. Approximately 24 per cent (1.6 million) of the population in Hong Kong is overweight. The evidence is clear: physical activity can decrease risk factors and ultimately reduce the chances of dying from cardiovascular disease. The lack of understanding in Hong Kong of the link between physical activity and health means the majority of the population is at risk of developing one or several lifestyle diseases.