Physical exercise is the performance of some activity in order to develop or maintain physical fitness and overall health. It is often directed toward also honing athletic ability or skill. Frequent and regular physical exercise is an important component in the prevention of some diseases such as heart disease, cardiovascular disease, Type 2 diabetes and obesity. Exercises are generally grouped into three types depending on the overall effect they have on the human body: Flexibility exercises such as stretching improve the range of motion of muscles and joints; aerobic exercises such as walking and running focus on increasing cardiovascular endurance; and anaerobic exercises such as weight training, functional training or sprinting increase short-term muscle strength.