It is known that humans can hold their breath underwater and undertake rudimentary locomotive swimming within weeks of birth, as an evolutionary response.
As a formalized sport, swimming features in a range of local, national, and international competitions, including every modern summer Olympics.
Many swimmers swim for recreation, with swimming consistently ranking as one of the physical activities in which people are most likely to take part. Recreational swimming can also be used for exercise, relaxation, or rehabilitation. The support of the water, and the reduction in impact, makes swimming accessible to people who are unable to undertake activities such as running.
Swimming is primarily a cardiovascular/aerobic exercise due to the long exercise time, requiring a constant oxygen supply to the muscles, except for short sprints where the muscles work anaerobically. As with most aerobic exercise, swimming is believed to reduce the harmful effects of stress. Swimming is also effective in improving health for people with cardiovascular problems and chronic illnesses. It is proven to positively impact the mental health of pregnant women and mothers. Swimming can even improve mood.