If the Heart Is a Muscle, Why Doesn’t It Get Tired?

You’re on the weight bench. 18. 19. 20! You couldn’t lift that barbell again if someone had a gun to your head. Your arms and your chest are sizzling with a dull burn. Your muscles are fatigued, and as you try to put the bar back, your arms give out.

Then there's a crash.

Dropping a barbell on yourself is one thing, but imagine if your heart just up and stopped whenever it got tired of beating. It would be disastrous and defibrillator makers would rule the world. We, and every other thing with a heart, would be extinct in no time.

Unlike the rest of your muscles, your heart expands and contracts, non-stop, all day and all night for your entire life without a break. How does it do it?

Your heart might be a muscle, but it isn’t quite like your biceps or your abs or your pecs. Those are all “skeletal muscles” and they’re attached to your bones. Your heart, meanwhile, is made of “cardiac muscle.”

Both of these types of muscles need energy to contract, and they both get it from mitochondria, the so-called “cellular power plants" that generate adenosine triphosphate (ATP) for the transfer of chemical energy. Cardiac muscle resists fatigue so well because it’s got more mitochondria than skeletal muscle. With so many power plants at its disposal, the heart doesn’t need to stop and chill out. It also has a steady supply of blood bringing it oxygen and nutrients.