7.1: Heart
- Page ID
- 55504
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The heart is an amazing muscle; it beats steadily throughout our lifetime—about 4 billion times. The pulse reflects how fast and hard the heart beats.
How much blood the heart pumps per minute depends on how fast the heart beats and how much is pumped with each beat. When we rest, our heart pumps about 5 quarts per minute. We have about 5 quarts, so this means that our entire blood supply is pumped through our heart each minute—about 0.3 cups per beat and 70 beats per minute in sedentary people. Endurance training increases the amount pumped per beat. An athlete’s resting pulse is slower, but can still pump 5 quarts per minute with about 0.4 cups per beat and 50 beats per minute.
How fast can blood circulate? An endurance athlete’s performance depends a lot on how fast substances (especially oxygen) are delivered to muscles and how fast waste is removed.
A world-class endurance athlete’s heart can pump about 40 quarts per minute (the fastest in sedentary college-age men is about 20 quarts/ minute)—the entire blood supply is circulated in less than 10 seconds. This is mostly from more blood pumped per beat, because the maximum heart rate in both athletes and sedentary people is about 200 beats per minute.
This difference between sedentary people and world-class endurance athletes may not, of course, all be due to training; some can be genetic. But endurance training does markedly increase the amount of blood the heart can pump with each beat.
Your heart is a muscle about the size of your fist. As shown in Figure 7.1, the right side of the heart (the unshaded side) pumps blood to the lungs, where carbon dioxide is removed and oxygen is taken up. The blood then returns to the left side of the heart, which pumps oxygenated blood to the aorta that then branches into vessels that supply the entire body. The heart itself is nourished by coronary arteries—the first branches off the aorta (Figure 7.2). Blockage of a coronary artery causes a heart attack.
