An activity requiring physical exertion. Everyone should take regular exercise: this keeps muscles in tone, maintains the CARDIOVASCULAR SYSTEM in good shape, helps to keep weight at an optimum level and promotes relaxation and sleep. When an individual is at rest, the heart’s output is 5 litres of blood per minute. When running at 12 km (7••• miles) per hour, this rises to around 25 litres, obliging the heart and lungs to operate more eﬃciently and speeding up the metabolism of food to provide the necessary energy. Lack of exercise by children may lead to faulty posture and ﬂabby muscles; in adults it results in an increase in weight and poorly functioning respiratory and cardiovascular system, with an increased chance of heart disease later in life. Adolescents and adults, participating regularly in sporting activities, should train regularly, preferably under expert supervision, to ensure that they do not place potentially damaging demands on their cardiovascular, respiratory and musculoskeletal systems. Those wanting to participate in demanding sports would be wise to have a medical examination before embarking on training programmes (see SPORTS MEDICINE).
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