What happens to your body when you run? Well, quite a lot happens, in fact. This article will briefly consider what happens when you head out the door and begin running; and what happens over a period of time – what one would call adaptation to training.
You pull on your shoes, head out the door and start to run. A lot starts to happen to your body, physiologically. It is fairly obvious that you will pretty quickly find yourself breathing heavily and rapidly; accompanying this, your heart rate will go up from somewhere around 70 or so beats a minute to as much as 200, depending on how hard you are exerting yourself and how old you are. (Your maximum heart rate decreases as you age). These respiratory and cardiovascular changes are all necessary to supply your exercising muscles with the large supply of oxygen, carried in the red blood cells, which they require for sustained exercise. After a while you will probably find yourself sweating, perhaps profusely.
Actually, the previous paragraph assumes that you are going out for a jog over several miles. Perhaps you are actually going for a sprint. There is a big difference between the two and it is not just how fast you are moving.
Respiratory and cardiovascular changes to your body when you run
Whether you sprint 100m or jog 5 miles, your muscles require energy. Nonetheless, the way in which that energy is obtained is very different. Ultimately, that energy requires chemical reactions involving fats or carbohydrates within your muscle cells using the oxygen supplied by the heart and lungs. However, sprinters are working anaerobically, meaning in the absence of oxygen. That is not to say that they are sprinting through outer space! It merely means that, even with the heart pumping flat out and breathing heavily, the cardiovascular and respiratory systems simply cannot supply oxygen to the muscles as fast as they might need it. The muscles have developed a mechanism for producing energy in the absence of sufficient oxygen; however, it only works for a limited time and you can only sprint for 30s or so. Eventually you stop and breathe very heavily for a minute or so. During this time, your body is paying back the so-called oxygen debt which it has accumulated.
If, however, you are jogging at a moderate pace, you can keep it going for several miles. Your heart and lungs can supply sufficient oxygen for your muscles to produce the energy which they need – they are acting aerobically. They will eventually tire but not for lack of oxygen.
Your muscles are wonderful but they are not tremendously efficient. A lot of the energy which they use is actually converted to heat and this must be dissipated by your body. This is why you sweat when you run. As the sweat evaporates from the skin, it takes heat with it, thus helping you to cool down. As clever as this may seem, it comes at a price. You are losing fluid from your body – you are becoming dehydrated – and this ultimately causes problems. As your blood is mostly water, it somewhat reduces the volume of blood in your body and plenty of blood is essential to supply the muscles with oxygen. It also reduces the amount of fluid in and around muscles cells which eventually leads to the stiffness which everyone who has run any distance has eventually felt. Eventually you must replace this lost fluid – it is a good idea to do so during your runs if you can.
Another way which the body uses to cool down is to circulate more blood to the skin. The blood carries heat with it, which then escapes from the body when it reaches the surface. However, this is where the body finds itself compromised. During a run, the body diverts blood to the muscles from other organs where it is not essential for the time being – the gut for example. However, blood flowing to the skin is blood not flowing to the muscles and that is not good when you are running.
The problems associated with dissipating heat from the body are why it is difficult to run your fastest marathon on a hot day. Cooler weather means less sweating and less dehydration.
You may have heard of the runner’s high. Whether you experience it or not is another matter. It is a sense of well-being, or semi-euphoria or similar which you usually feel shortly after a run – or other forms of exercise – and is very pleasant and may last for an hour or two. It is believed to be due to the release of endorphins, the brain’s natural feel-good chemicals.
Long term effects on your body when you run
Increased heart rate, increased breathing, sweating – these are short-lasting physiological changes which occur during your run. What about the long term effects of running?
Long lasting changes in your body are what you are aiming at with training. Perhaps you want to lose weight. If you run enough, your body will gradually use up the fat stored around your stomach to provide to the energy for your runs. Perhaps you want to run faster, or further. There will be physiological changes which allow you to do just that. The main adaptations to distance running occur to the cardiovascular system and the muscles. Changes will occur to your heart allowing it to pump blood around your body more efficiently. You should notice this as a lower resting heart rate (you find this by taking your pulse when you are sitting quietly doing nothing strenuous). Your heart improves to pump more blood with each beat and it can therefore beat more slowly and supply the same amount of blood. To help improve the flow of blood to your muscles themselves, new blood vessels will grow within the muscles. The muscles themselves will adapt to training. They may become larger; they will become more efficient at using the energy sources provided to them. These changes will allow you to run further, longer and faster.
A lot happens to your body when you run. In the long term most of it is good. So get out there, and get running!