Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: thedoc on 19/09/2013 08:13:57
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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?
Asked by Ahmed Youssef
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Heart muscle (https://en.wikipedia.org/wiki/Cardiac_muscle#Metabolism) is different from the muscles attached to the skeleton (https://en.wikipedia.org/wiki/Skeletal_muscle).
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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.
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Since the human heart is a muscle, why doesn't it get sore from intense exercise such as conditioning?
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 (http://en.wikipedia.org/wiki/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.
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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.
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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!
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But the heart truly is an amazing muscle. It pumps about 7,600 liters a day, non-stop.
"non-stop" is misleading, an individual heat muscle will be at rest for part (most?) of the duty cycle (https://en.wikipedia.org/wiki/Duty_cycle).
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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.
"non-stop" is misleading, an individual heat muscle will be at rest for part (most?) of the duty cycle.
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.
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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.
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I have a close friend, she is a female weighing in at 600lb but she is 30 & mobile enough, she wants to keep her weight and try to avoid as little health problems as possible. To achieve this she does aerobic exercises, plenty of water, eats cinnamon, fiber, cardamom, and flaxseed. She does not want to lose the weight but has developed some muscle under her fat. Will her heart gradually adapt to the workload? Does the muscle apply more of a strain? If she has a well balanced diet, can she have minimal health problems whilst still keeping her girth? With plenty of natural supplements and calm yet lengthy conditioning will her body be able to sustain the weight or will she inevitable succumb to heart failure?
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There are two ways in which a heart can get bigger. The size of the main chambers (the ventricles) can increase so that each beat of the heart can pump more blood and the thickness of the heart wall (ventricular muscle) can become thicker so that the pressure that the heart can produce will increase. We call the increase in chamber size eccentric cardiac hypertrophy and the increase in wall thickness concentric hypertrophy. Eccentric hypertrophy is a normal response to endurance training and is, in large part, the cause of the higher 'cardiac outputs' that trained athletes can produce. It is thought to occur as a result of an increase in blood volume (plasma volume) as a result of exercise. This increase in plasma volume probably arises due to an increase in the protein albumin in the blood as a result of a redistribution of albumin from the interstitial space. The greater plasma volume is transient, which is why exercise has to be continually repeated on almost a daily basis and it causes a greater return of blood to the heart (venous return). This increased venous return quite literally stretches the heart making it bigger - and the heart gradually over time accommodates this stretch and becomes bigger. Concentric hypertrophy probably results from the same type of signalling as in skeletal muscle, although I know much less about it. Whilst some have looked at the time course of both concentric and eccentric hypertrophy during a ramp in exercise it is likely to be complex and dependent on the starting state of the heart. The system is complex because heart rate also changes with exercise and the change in heart rate probably alters the resting heart volume. Whilst acutely, at rest, parasympathetic tone alters heart rate there is now increasing evidence that in athletes there is a change in the expression of ion channels rather than parasympathetic tone that underlies the lower heart rate. There is still a lot that is unknown...
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Thanks @Christof Schwiening
To add to the above, readers might like to take a look at the recent programme we made about "hearts in extremes" recorded at the British Cardiovascular Society meeting (https://www.thenakedscientists.com/podcasts/naked-scientists-podcast/hearts-extreme), 2017.
Specifically, this interview with Sanjay Sharma talks about how the heart adapts to exercise (https://www.thenakedscientists.com/articles/interviews/athletes-hearts).