Physical exercise is any bodily activity that raises the heart rate above its resting level and enhances or maintains physical fitness and overall health. It is performed for many different reasons. These include: strengthening muscles and the cardiovascular system, honing athletic skills, and weight loss or maintenance. Frequent and regular physical exercise boosts the immune system, and helps prevent the "diseases of affluence" such as heart disease, cardiovascular disease, Type 2 diabetes and obesity. It also improves mental health and helps prevent depression. Childhood obesity is a growing global concern and physical exercise may help decrease the effects of childhood obesity in developed countries.