The Heart of the Matter

What really happens to your body when you start running further and faster? Dr Jason Chia reveals the inner workings of the body’s cardiovascular system and how running makes it more efficient.

Have you ever wondered what happens to your body with all that training? Why does running become easier when you first decide to run regularly for a few months? How do those additional kilometres of running that you put in before the race translate into a personal best?

One of the main reasons for the improvement in performance with training, especially in the earlier stages, is due to the changes in the body’s circulation system. These can happen to the heart, the blood vessels and components of the blood, including the volume of the blood available in circulation as well as the red blood cells, down to the pigment that is responsible for transporting oxygen to the working muscles. In essence, the circulation system becomes a better logistics chain in gathering oxygen from the lungs and transporting it to the muscles, supporting the efficient burning of fuel that is necessary to maintain prolonged running.

The heart, like the other muscles in the body, responds to training by getting bigger in volume. In distance running, the heart has to adapt to the task of pumping large volumes of blood quickly in order to supply oxygen to the working muscles. With training, the chambers of the heart enlarge and to a lesser extent, there might be thickening of the walls of the heart as well. The net result is that with each contraction, it forces more blood out, enabling a greater output during exercise. Conversely, at rest, when the demands are low, it has to contract fewer times than before to maintain an operating blood supply to the body. The drop in resting heart rate with training is accounted for in part by this phenomenon and is one of the signs of improved cardiovascular performance.

However, if there is not enough blood for the heart to circulate, there would be no performance gain. One of the adaptations to training happens at the kidneys which essentially results in greater retention of water in the body, as well as production of proteins in the liver that keeps more water in the circulation system.

However, Man’s ability to do continuous running in hot conditions without over-heating is because we sweat to keep the body cool. Perspiration draws from the same supply of water in the body. That is one reason why dehydration can impair running performance (in essence, it can undo some of the effects of hard training). Other training adaptations occur at the level of the red blood cells. These multiply and the concentration in each cell of the pigment that carries oxygen (haemoglobin) also increases. Furthermore there is also a change in the type of haemoglobin which is more efficient at releasing the oxygen where it is needed. Think of it as having more delivery trucks which pack more cartons and the cartons are better designed to be off loaded at the destination.

Such is the importance of these adaptations in the blood that athletes who engage in clandestine attempts to cheat at major events do so by using a variety of methods to gain an unfair advantage, including blood transfusions or by using hormonal injections to magnify these changes.

The Heart of the Matter 

With continued training, the body undergoes further adaptation at the level of the small blood vessels in the muscles that undergo training. Fine blood vessels grow from the existing ones to reach out to the muscles, cutting down the distance that the oxygen has to drift to the muscles cells. The latter is one of the reasons why even in endurance sports, the improvement in fitness is activity-specific. For example, when you improve in running, you might also see improvement in your swimming but to a smaller extent as the muscles which are used during the training undergoes adaptation.

Quite apart from improved running performance, running as an activity also brings benefits to cardiovascular health and overall wellbeing in general. It has been well known that improved cardiovascular aerobic capacity is associated with less cardiovascular disease. Part of the reason can probably be explained by the effect of regular exercise on reducing the risk of developing (or helping to control) chronic diseases such has hypertension, diabetes, dyslipidemia and obesity which are risk factors of cardiovascular diseases. In addition, exercise has an independent effect on decreasing systemic inflammation and improving the function of the innermost lining of the blood vessels, decreasing the likelihood of plaques forming and narrowing of the blood vessels, particularly those that supply the heart. Regular runners might also probably be habitually active through the day. Sedentary behaviour, especially prolonged continuous periods of inactivity, is in itself associated with increased risk of developing cardiovascular disease, regardless of physical activity.

Despite the benefits that can be accrued by regular running, running can be a physically stressful activity for the heart. When it is not in good health, the stress of vigorous exercise sometimes causes insufficient blood flow to the heart. This might cause chest pain or chest discomfort. In very rare cases it might trigger irregular heart rhythm which can be fatal. It is for these reasons that those at risk of developing heart disease should consider having the risk evaluated and their cardiac health assessed before engaging in vigorous running. Those with underlying risk factors might still engage in running after these factors are well controlled and have a gradual increase in running intensity built into a running programme. With these provisos, the overall benefits of health far outweigh the transient increase in risk brought on during the running.

Dr Jason Chia is currently head of Sports Medicine and Surgery Clinic (SMSC) at Tan Tock Seng Hospital and holds a post-graduate specialist degree, Masters of Sports Medicine, from Australia. His clinical interests include sports injury management, fitness testing and exercise prescription, dance medicine, and extracorporeal shockwave therapy. Dr Chia is also a member of the Singapore National Olympic Council Olympic Medical Committee and Deputy Chief Medical Officer of the SEA Games Medical Committee.

Originally published in RUN Singapore.