(HealthDayNews) -- What happens when you push yourself to physical extremes?
The heart boosts its pumping capacity five-fold, from a gallon a minute to more than five, to deliver vital oxygen to where it's needed. Most of it's needed by your muscles, which will get almost 90 percent of your body's entire blood supply, says Adrian Smith, author of The Body.
At rest, your muscles get about two pints of blood a minute. At maximum exertion, they get almost 40 pints a minute. While the heart increases output by five times, the muscles need 18 times their usual supply of blood.
To supply the muscles, the blood is diverted from other organs: the kidneys are reduced to about a quarter of their normal supply; the digestive system gets only a fifth of its usual blood flow. The heart itself requires four times as much blood during peak exertion, but the brain apparently is unaffected by the extra physical activity. At rest it gets about 1.5 pints a minute, the same amount it gets during the most strenuous exercise.
