The heart works at an average rate of 72 beats per minute, which is equivalent to 104,000 per day, approximately 38 million per year. But if the heart is a muscular organ, why doesn’t it get tired of beating? This is one of the mysteries solved by science over the years.
First, we need to understand that there are three types of muscle: skeletal, which is attached to bones through tendons, as in the arms and legs; smooth, which can be found in the wall of hollow organs, such as the bladder; and, of course, the cardiac, which covers the heart and allows the movements and transport of blood to other organs.
Heart muscle is made up of special cells called cardiomyocytes, and unlike other muscle cells in the body, cardiomyocytes are highly resistant to fatigue. Normally, mitochondria (responsible for providing energy to the cells) feed the muscles, and this also applies to cardiomyocytes. However, they have up to 10 times the density of mitochondria, triggering their energy production. This helps explain why the heart doesn’t get tired so easily.
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The heart can get tired, under extreme conditions
In 2001, a professor of cardiology conducted a study of 50 Scottish athletes to understand the heart’s level of resistance. At the time, the researcher discovered that it is possible for the heart to get tired, but under extreme conditions.
Before and after an arduous race, the athletes had electrocardiograms and ultrasounds. Scientists noticed that the hearts of these athletes pumped 10% less blood at the end of the race compared to the amount pumped at the beginning.
At this point, you might be wondering why not all muscles are made of cardiomyocytes, because then everyone could be fit without worrying about getting tired. It turns out that cardiomyocytes contract without a nerve supply, so they are incapable of voluntary and intentional movements.
Still, it should be said that muscles can be classified as voluntary, that is, when their contraction is coordinated by the nervous system, which is influenced by the person’s desire; or involuntary, when the contraction and relaxation of the muscle does not depend on the person’s will – as is the case with the heart.
