If the heart is a muscle why doesn't it ever get tired like an arm or leg?

With the heart beating non-stop (hopefully) for your entire life why doesn’t it tire? Why can’t you feel the burn like you do when you do pushups or running? Doesn’t it fill up with lactic acid, or whatever it is that makes your arm muscles burn when pumping iron? Is there a mechanism that prevents this?

It’s probably the same reason why your tongue doesn’t get tired when you talk a lot.

The heart rests between beats.

The heart is conveniently located near the best damn blood supply and oxygen supply because…ironically, IT’S the HEART.

It does rest between beats and, when stressed if not in shape, will hurt.

Muscle aches and pain come with forcing muscles beyond range of motion (try that with your heart), or forcing an abnormal load and forcing tears, and forcing depletion of internal muscle resourses.

You cannot do that to the (healthy) heart. The other muscles will give way first, usually, in your attempt to exhaust yourself (heart).

But, people do get chest pains, and fatigue as well, which are your stress limits for your heart - sort of.

There are three major conditions (“major” meaning get to a doctor, fast) that can cause heart pains after exertions:
[ul][li]Angina is a condition of chest pain that result from your heart getting an inadequate blood supply, typically after exertion.[/li][li]An infarction (heart attack) happens when a blood vessel to the heart is completely blocked, with pain symptoms considerably worse than angina, and the chance of permanent damage to the cardiac muscles.[/li][li]A rather charming condition called constrictive pericarditis that involves the swelling or hardening of the pericardium, the protective sac around the heart. In this case, the heart cannot expand enough and simple exertion (like walking) can cause pain, dizziness and in extreme cases, death. The condition can be corrected by drugs or surgery.[/li][/ul]

None of these are simple fatigue, as a normal muscle might feel. Fact is, if you keep your blood vessels clear and avoid major infections, your heart should be good for 2-3 billion beats.

It gets a lot more regular exercise than your arms do, so it’s always in tone.

I wish you hadn’t said that. I have always had a relatively fast heart rate, like up around 80 at rest. Assuming an average of 70 over my lifetime, I’m already at 3 billion.

Also, the heart is made of a different type of muscle tissue than arms and legs and all the other parts you can move voluntarily (with the possible exception of your lungs).

The heart is made of involuntary muscles, so it works differently than your deltoids and biceps.

The lung is not muscular. The diaphragm is.

Urban Ranger

True, but the heart muscle is a different kind of muscle tissue from either the typical (smooth) muscle tissue of involuntary muscles or the typical (striated) muscle tissue of biceps and etc. IIRC, its fibers are shaped like little Y’s. At any rate, it may be tissue ideally suited for continuous work.

(I’ve heard that uterine muscle is pretty impressive too).

True, but as far as this discussion is concerned, it’s probably not an important distinction.

I have had tongue fatigue after giving long lectures and such. It aches just like a sore muscle.

It will eventually get tired, someday-but not for a long, LONG time.

As long as it’s taken care of.

One factor is that the cells of the heart have many more mitochondria than, say, biceps cells. Mitochondria are the organelles (mostly) responsible for converting sugars to ATP, the stuff your cells actually use for fuel, so the side effect is that the heart burns a lot more calories, for its mass, than other muscles in the body.

While this is true, and nice to know, it doesn’t get at the heart of the OP.

First, pain associated with muscle pain is very often ligament and/ or tendon related.

Secondly, actual muscle fiber need to be ‘torn’ to ache for a while.

Also, range of motion beyong typical range of motion can change different parts of the fibers in different ways.

Muscles tend to ache when the normal pattern they adapted to changes. They need to flex farther, or tighter, or lift more.

These things are major contributors to muscle pain, and the heart never has to deal with them. These factors, along with what seems to be a different type of muscle fiber, are the reasons your heart won’t get sore under most circumstances as you other muscles (or connected parts) would.

Well, you’re past warranty and should package yourself in your original container for shipment back to the factory for refurbishing.

Is this true? It may be, but the brain’s only source of energy is sugar. The heart weighs from 250 grams to over 300 grams in the “athlete’s heart.”

Comparing heart muscle to voluntary muscle (striated muscle) is really comparing apples and oranges. As noted previously, cardiac muscle consists of fibers that branch and connect with adjoining fibers, forming a synctium. The fibers are striated, as voluntary muscles are, but the striations are less pronounced. Moreover, the nuclei are located in the central portion of each fiber, unlike voluntary muscle, which consists of fibers made up of large, multinucleated cells, which do not undergo mitosis, and are located near the periphery.

Voluntary muscles act by a ratcheting method in the sacoplasms, in which the contractile elements (myofibrils) are embedded.

The heart muscle never rests. It is always beating, but when you are at rest, it beats less often, of course. It acts due to certain nerve impulses and you don’t have the ratcheting method used by voluntary muscles. (Volunary muscles are enervated as well, but the heart has special muscle fibers, atypical fibers, called Purkinje fibers, providing the impulse conducting system.) Your nervous system never rests. Since your nervous system doesn’t rest and signals are constantly sent to the heart, neither does your heart. (Nerve signals are not constantly conducted through voluntary muscles.) You cannot strain your heat as you can voluntary muscle. If you overexert yourself, the heart may not be able to supply enough oxygen for your activity and you will have to stop. Also, the heart arteries may not be able to supply the heart with enough blood and you will suffer a myocardial infarction. This is particularly true if you have some coronary blockage. It probably is not true for a healthy heart, but then your nerves may go haywire, resulting in fibrillation. I don’t believe that one who exercises regularly and has a healthy heart will suffer those consequences.

I read that the heart’s actually resting about sixty percent of the time, more in people with better-conditioned hearts - the hearts pump more effectively with every stroke, and thus, don’t need to beat as often, so their hearts get more rest. It sounds about right; I should really search Google and find proof, but I’m about to go on a jog. My own vital knot of heavily-striated involuntary muscle hasn’t had his daily punishment yet.

Involuntary muscle is non-striated or smooth. Each fiber has a single nucleus, located in the center.

By the medium of the Purkinje fibers, nerve impulses are conducted which regulate the beat of the heart. The heart beat is a continuous action. An athlete’s heart may beat as little as 40 times a minutes. (Mine has been less than that when well rested.) Normal is 60-70. When the left ventricle contracts, this correlates to the systole of the heart beat n pressure, and can be seen on the EKG as the Q-S interval. When it relaxes you have the diastole, which when converted into blood pressure is normally 120(systole)/70 (diastole). Blood is continuously being pumped throughout the body by the heart, but with less pressure when the left ventricle relaxes. The period of relaxation is the refractory period. In a heart that beats at 70 times a minute, the refractory period is 0.3 seconds. This is actually 66 times that of skeletal muscle. So, in a sense, it rests, but the beat goes on.