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The Evidence Exercise – What Happens to Our Heart When We Exercise? | Episode 3

The Evidence Exercise – What Happens to Our Heart When We Exercise? | Episode 3

Last week Stephen walked us through the basic recommendation for physical activity, as laid out by the NHS. Today, we begin to discuss cardio-vascular health.
This weeks episode asks “What happens to our heart when we exercise?… and when we don’t?”
Check out the full blog and resources below and tune in next week where we talk about cardio-vascular health and the arteries!

Cardiovascular health is essentially the health of your heart, arteries, veins and blood vessels, and as we touched on in the last video, scientific and medical research has shown that taking part in regular physical activity has major health benefits with regards to the cardiovascular system. For example, people who meet recommended physical activity guidelines (NHS choices) are at:

  • 35% lower risk of developing coronary heart disease and/or stroke, than people who don’t get enough physical activity (Kokkinos, 2012)

The main type of exercise that will be of most benefit to the cardiovascular system is commonly called AEROBIC EXERCISE. This is the type of exercise that the NHS guidelines are referring to as moderate-vigorous physical activity (Running, tennis, walking etc), and it is dependent on the presence of oxygen in the bloodstream as the main energy source.
So WHY does getting enough exercise, in particular aerobic exercise, reduce your chances of developing heart disease, or having a stroke by over a third (Shiroma and Lee, 2010) compared to people who don’t meet guidelines?
To answer this question, we will briefly run through what happens to the body as a result of regular physical activity, compared to what can happen if you don’t get enough exercise, and how this can prevent the development of harmful health issues.
As we said before, aerobic exercise primarily uses oxygen to fuel the muscles. This oxygen is transported to the muscles in the bloodstream, meaning the heart has to work to pump enough blood throughout the body to supply the muscles with enough oxygen to keep them moving, and to supply them with other nutrients in the blood. So when we do exercise such as running, cycling even fast walking, our heart rate increases as the extra demand for oxygen from the muscles is met by the heart. Regularly causing the heart to increase its blood flow will cause the chambers of the heart and in particular, the left ventricle (which is responsible for pumping oxygen-rich blood throughout the body) to adapt and be able to hold more blood to pump around the body (as we demonstrate with our diagram in the video). This means that the left ventricle can now hold a larger volume of blood inside it, which means it will pump more blood around the body with each beat, ultimately taking strain off the heart and slowing the resting heart rate. (The heart can also enlarge due to the constant stress put on it by high blood pressure, but this will ultimately lead to heart failure, and is not the same as a heart that is large due to exercise).
What does this mean for the arteries and blood vessels?
As we age, our arteries steadily lose what is medically called their compliance, which is simply their elasticity or ability to stretch to allow blood to be pumped efficiently around the body (the stiffer they are, the more force the heart has to produce to get a sufficient stretch in the artery). Recent studies have shown that:

  • Taking part in regular recreational activity, especially vigorous exercise can slow down the rate that people’s arteries stiffen with age (around a 50% reduction among the most active study participants) (Joyner, 2000).
  • 3 months of aerobic exercise training was enough to reverse the arterial stiffening in middle-aged and older participants who were not physically active before taking apart in the study (Tanaka et al., 2000). Which means that it’s never too late to get a healthier cardiovascular system!

Another problem related to stiff arteries, is that a mixture of bad diets and a lack of physical activity can lead to a build-up of “bad” cholesterol in the bloodstream, and a decrease in “good” cholesterol. Over time, this can lead to the bad cholesterol and dead white blood cells (which try to attack the bad cholesterol as it builds up) being left behind on the artery walls as plaques, leaving less space for blood to be pumped through. Over time, there is a risk that these deposits can cause blood clots either by rupturing or becoming too big, leading to heart attacks, or if the vessels in the brain are affected, a stroke. Blockages in the arteries of the legs can cause peripheral arterial disease, where poor circulation to the lower extremities makes walking painful and the healing of wounds more difficult for the body, in extreme cases, this can lead to amputation of the limb. The good news is that increasing physical activity combined with watching what you eat, can prevent and even reduce the amount of bad cholesterol in the bloodstream, which helps the arteries to stay clear of blockages due to cholesterol build-up. It’s important to remember though, that exercise alone doesn’t work as well at controlling bad cholesterol when compared to both exercise and a healthy diet, which recent research has shown us (Kelley et al., 2012). However, once cholesterol deposits do form on the arteries, they are pretty much there to stay, which is why it’s so important to prevent them forming in the first place, or to make changes to your lifestyle so that any plaques that are there do not increase in size. Regular exercise also increases the size of the capillaries which carry blood around even the smallest parts of the body. This also applies to the capillaries which surround the heart muscle (myocardium) as the heart also needs a good, oxygen rich blood supply to work properly.
So, people who don’t do enough physical activity will generally have a heart that is having to work harder with each beat, while pumping less blood around the body, which may lead to coronary heart disease, high blood pressure or risk of having a stroke. Add on top of that the effects of arterial compliance and bad cholesterol, and you can see why the risk of cardiovascular disease is much higher in people who are sedentary (don’t do any physical activity) than in people who live active lifestyles. Especially as we get older. Making sure you meet the guidelines for physical activity will mean that your heart will not work as hard at rest, as it will have adapted to hold more blood, and to pump this blood with more force around the body. This is why people who are highly trained (such as athletes) usually have lower resting heart rates and blood pressure than the average person, that doesn’t mean you have to be an athlete to get the health benefits, just making sure to meet the guidelines is enough to significantly reduce your heart rate during rest, and can have positive effects on blood pressure too.
But doesn’t lots of exercise cause heart attacks?

  • Contrary to popular belief, 90% of heart attacks happen when at rest
  • The stats –how rare are sudden cardiac problems during exercise- for adults without a pre-existing heart condition, the occurrence of a heart problem during exercise is between 1 in 400,000 to 1 in 800,000 hours of exercise. Even for people with an existing heart condition the risk is still quite low, with 1 in 62,000 hours of exercise (Myers, 2003).
  • Remember to BUILD UP GRADUALLY! Those who do experience a cardiac event during exercise are mostly people who either have a pre-existing heart condition, or are unfit and do too much too fast. In fact, research shows that a sedentary person’s risk of cardiac event during exercise is about 50 times higher than someone who exercises 5 times a week. Sweating, heavy breathing and an increased heart rate are all normal healthy reactions to vigorous physical activity. However, if you start to feel faint, dizzy, and nauseous or get chest pains, this is a sign you may be pushing yourself too hard and you should take a break, or if you experience chest pains, seek emergency medical attention. There is also a growing number of scientific studies emerging that indicate extremely extensive aerobic exercise (i.e. a marathon) and overtraining might damage heart muscle and arteries (Siegel et al., 2001, Wilson et al., 2011), but such levels of exertion are hard to reach for the average person, and more scientific evidence is needed to say definitively that this is the case, as scientists are still debating whether this is true or not (Yared and Wood, 2009). But what is clear, is that you should stay within your limits, don’t overdo it.
  • As we said before, people who don’t exercise enough usually have a weaker heart, may have cholesterol plagues in the arteries and depending on their age may have arterial compliance. So of course if they decide to suddenly over-stress their already overworked heart by going out and suddenly doing a ton of exercise, they could be in trouble.
  • In summary the benefits of taking part in regular physical activity far outweigh the tiny risk of having a heart attack due to exercise. So don’t be put off by this, research shows that you are far more likely to die from heart disease due to doing no exercise, than by a sudden heart attack from doing regular exercise. If just starting out on an exercise routine after a long time being sedentary, remember to take it easy to start off with and gradually add to the amount and intensity of your physical activity as your heart adapts to the increased stress. If you have been diagnosed with a heart condition OR a respiratory condition, always consult your doctor before taking part in a new exercise regime.

We hope you have found this info helpful, stay tuned for our next episode of the Evidence Exercise next week!
JOYNER, M. J. 2000. Effect of exercise on arterial compliance. Circulation, 102, 1214-1215.
KELLEY, G. A., KELLEY, K. S., ROBERTS, S. & HASKELL, W. 2012. Comparison of aerobic exercise, diet or both on lipids and lipoproteins in adults: a meta-analysis of randomized controlled trials. Clinical nutrition, 31, 156-167.
KOKKINOS, P. 2012. Physical activity, health benefits, and mortality risk. ISRN cardiology, 2012.
MYERS, J. 2003. Exercise and cardiovascular health. Circulation, 107, e2-e5.
SHIROMA, E. J. & LEE, I.-M. 2010. Physical activity and cardiovascular health lessons learned from epidemiological studies across age, gender, and race/ethnicity. Circulation, 122, 743-752.
SIEGEL, A. J., STEC, J. J., LIPINSKA, I., VAN COTT, E. M., LEWANDROWSKI, K. B., RIDKER, P. M. & TOFLER, G. H. 2001. Effect of marathon running on inflammatory and hemostatic markers. The American Journal of Cardiology, 88, 918-920.
TANAKA, H., DINENNO, F. A., MONAHAN, K. D., CLEVENGER, C. M., DESOUZA, C. A. & SEALS, D. R. 2000. Aging, habitual exercise, and dynamic arterial compliance. Circulation, 102, 1270-1275.
WILSON, M., O’HANLON, R., PRASAD, S., DEIGHAN, A., MACMILLAN, P., OXBOROUGH, D., GODFREY, R., SMITH, G., MACEIRA, A., SHARMA, S., GEORGE, K. & WHYTE, G. 2011. Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes. J Appl Physiol (1985), 110, 1622-6.
YARED, K. & WOOD, M. J. 2009. Is Marathon Running Hazardous to Your Cardiovascular Health? The Jury Is Still Out 1. Radiology, 251, 3-5.
“The Evidence Exercise” is a nine-part series focusing on the research and evidence for including physical activity in our lives.
You can watch the series here on the SCPHRP website or subscribe to the SCPHRP YouTube channel to be alerted when new videos go up. Be sure to follow us on Instagram, Facebook or Twitter for behind the scenes photos and information.
Made with funding from The University of Edinburgh’s ‘Innovation Initiative Grant’.



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