Science Questions

Does exercise lead to a bigger heart?

Sun, 29th Apr 2012

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Ahmed Youssef asked:

I was wondering about the fibres in the muscle of the heart. I understand that most muscles in the rest of our body become thicker and bigger as a response to intense workout such as lifting weights or anything like that, but when we do cardio intensive workouts, does that lead to the same response? Does that create a physically bigger heart?


Chris -   Well actually, it does cause a bigger heart and it can happen for both good reasons and bad reasons.  If you have a very high workload on your heart because you, for instance, have high blood pressure all the time, then you can develop cardiac hypertrophy and this is where the muscle of the Normal heart midventricular transverse sectionheart becomes thickened, bigger, and beefier in order to do more work and overcome the extra load applied to the heart by the high blood pressure.  Now, that's a bad thing, obviously; sometimes the muscle can become so big that, in fact, it has an oxygen demand which is bigger than the coronary arteries are capable of delivering via the blood.  So, people can get angina pain in their chest caused by the heart not getting enough oxygen because the heart has become pathologically large.

More normally though, people who do a lot of exercise along the lines of what you've been describing, Olympic athletes for example, footballers for example, you'll often hear them say that their resting pulse rate is really low.  They might say, for example, that compared with a normal person who has a resting pulse rate of say, 70 beats per minute, their heart beats only 40 or maybe in some cases, 30 times per minute.  Now the reason that can get away with beating more slowly is because the heart has become larger in response to their regular training and the demands they place upon it.  And that means that because its bigger, its working more efficiently.  With every beat of the heart, it actually pumps out more blood than a smaller heart in an untrained person.  So, as a result, they don't have to make their heart beat as often because every time it does beat, it pumps out two beats worth of blood, so their pulse rate can come down.  And, if you measure the maximum output from their heart, youll find that their maximum output can be say, 30 litres in a minute when they're working really hard, compared with say, 25 litres in someone whos unfit and untrained.  However, the maximum number of beats their heart can make in a minute will be lower than an unfit person because a bigger heart takes longer to fill up with blood, so they have to slow down their pulse rate and they just make their heart eject more.  This form of cardiac enlargement is not thought to be bad for you.  Its a physiological response to increased workload and, in the short term at least, we think that it isn't harmful.


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Heart muscle is different from the muscles attached to the skeleton.

RD, Mon, 12th Mar 2012

The heart does infact get tired.
It only takes about a century (+/- 30 years or so, depending on the individual)...

A lot of people that died of old age while being in perfect health died because their heart was tired. Nizzle, Thu, 15th Mar 2012

Sore. Yes, cardiac muscles are highly resistant to fatigue, and do not so easily fatigue as skeletal muscles, yet they do undergo stress that causes them to grow in order to pump higher volumes (usually in response to aerobic exercise) or to pump higher pressures (usually in response to anaerobic exercise). 

So, when we exercise so much, either aerobically or anaerobically, that causes the heart to grow, why don't we feel "sore" in our hearts? I would say that everyone would admit that their hearts feel perfectly fine, even when the rest of their bodies are exhausted, except when they're having heart attacks or something similar (angina pectoris).

I think the answer involves the "referred pain" one feels when suffering a heart attack and other disorders (including "ice cream headaches"). Classically, heart attacks are "felt" in the upper left section of the body -- left shoulder, left arm, left side of the jaw -- and also the neck, shoulders and back. My guess would be that a sore heart caused by exercise might feel like it's coming from these areas and not from the center of your torso where the heart is actually located. Lmnre, Thu, 15th Mar 2012

I'm not completely sure why the heart muscle wouldnt be sore after exercise. With skeletal muscles, the soreness after exercise is the result of lactic acid build up, and inflammation resulting from microscopic tears in muscle fibres. Inflammatory chemicals released from damaged cells stimulate pain receptors in skeletal muscles So the question would be, does the same kind of inflammation happen in the heart and does the heart have any pain receptors that are sensitive to inflammation? Or do pain receptors in the heart only respond to being severely deprived of oxygen?

According to an e-medicine article, angina or pain caused by ischemia is the result of  ATP being degraded to "adenosine, which, after diffusion to the extracellular space, causes arteriolar dilation and anginal pain. Adenosine induces angina mainly by stimulating the A1 receptors in cardiac afferent nerve endings." Unless you  already have heart disease, I doubt you could exercise to the point of inducing angina in a healthy heart, because blood would be shunted away from your arms and legs first and make you stop.

Both exercise, and oxygen depletion due to disease, cause the heart muscle to enlarge. But hypertrophy due to exercise results in more muscle mass and stronger contractions or  pumping ability. Enlargement due to disease results in more collagen or scar tissue, which doesnt increase the force of contractions, but does increase the volume of blood being pumped out somewhat, simply because the heart is now a larger container.

But the heart truly is an amazing muscle. It pumps about 7,600 liters a day, non-stop. cheryl j, Thu, 15th Mar 2012

I think that when your heart is fatigued although it is not felt directly the symptoms are exhibited elsewhere throughout the body both physically and mentally.  Personal experience has demonstrated that as I had a long standing un-diagnosed heart problem and was diagnosed as having extreme muscle fatigue in my left ventricle.  I can only say that leading up to the chance discovery of a problem, I was not feeling right! I was more stressed for no particular reason and would get tired quickly for no reason. 

Can the health of our heart effect our emotions?  Maybe it's not the heart that gets tired, it's us! Aaron_Thomas, Fri, 16th Mar 2012

"non-stop" is misleading, an individual heat muscle will be at rest for part (most?) of the duty cycle. RD, Wed, 21st Mar 2012

A couple reasons.

Cardiac muscle is ~70% Mitochondria by volume, where as skeletal muscle is around 5%. This makes a tremendous difference.

The heart is only a short coronary artery away from oxygenated blood. No problem with aerobic respiration.

It isn't really misleading to say such. Resting is part of the pump, allowing it to fill. If a heart was in constant contraction, no blood would flow through it. Domnomnom, Thu, 22nd Mar 2012

There is a series of medical conditions which result in an enlarged heart, because the heart is having trouble pumping blood around the body, and this struggle goes on 24 hours per day.

This should not be confused with healthy exercise where the heart and the blood vessels cooperate and grow as a result of exercise so they pump blood more easily around the body. As soon as the vigorous exercise is finished, the heart rate and blood pressure drops, usually below the level of a sedentary person. evan_au, Thu, 15th Nov 2012

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