DNA Explainer: Human heart beats about 100,000 times a day - Here's why it never gets tired

We are alive as long as our heart is beating. The moment the heart stops beating a person is announced medically dead. Anywhere from 60 to 100 times, our heart beats every minute of a day consisting of 24 hours. Roughly every day it beats about 100,000 times. But the surprising thing is unlike the other muscles in our body, our heart almost never gets tired, until it stops for good.

We all know that with growing age there is a lot of wear and tear in the body. Certainly, with age, our muscles and bones, which comprise our body tend to get weak and does not function with the same agility like it use to do before. But imagine if the same would have applied to our heart muscles then what would have been our plight?

So the obvious question that comes to our mind is why the heart muscle does not become weak with age like other muscles in the body? For that first, let's take a look into the muscle composition of the human body.

Different muscles of the human body

The human body is composed of three types of muscles - skeletal, smooth, and cardiac.

Skeletal muscles are striated (banded) and are what most of us think of when we envision a muscle.

The skeletal muscles which are attached to the bones and tendons, control almost all voluntary, and some involuntary body movements.

Like the cardiac muscle, skeletal muscle derives its energy from mitochondria within its cells.

Supplementing its mitochondria reserves, skeletal muscle can use glycogen (stored energy) to produce ATP, which transports and releases energy across cells.

Found in our hollow internal organs (except the heart), smooth muscle has no striations.

Smooth muscles work automatically, helping you digest food, dilate your pupils, and go pee.

Like skeletal muscle, cardiac muscle is striated. Uniquely, the cells of this kind of muscle are joined strongly together at adherens junctions.

This enables the heart to contract forcefully without ripping the fibers apart.

Why heart muscle is unique

Our heart muscle is not quite the same as our skeletal muscles such as the biceps and quads that are attached to the bones.

This is primarily because the heart is made of cardiac muscle, consisting of special cells called cardiomyocytes.

Unlike other muscle cells in the body namely skeletal and smooth muscles, cardiomyocytes are highly resistant to fatigue.

Cardiomyocytes are primarily powered by mitochondria (the energy house of the cell), similar to your other muscles.

However, cardiomyocytes have as much as 10 times the density of mitochondria, skyrocketing their energy output.

The cardiomyocytes have also evolved to have an enhanced blood supply, being better than ordinary muscle cells at extracting oxygen from the blood.

Cardiomyocytes contract without nerve supply, making them incapable of voluntary and purposeful movements. 

But when it comes to beating constantly and without tiring, the heart muscle works superbly.

Also, the heart has another secret weapon. It is flexible in terms of fuel, able to consume glucose, free fatty acids, and lactate.