What’s happening to our body when we run?

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We are perfect running machines. Image by Paul Petch.

We are perfect running machines. Image by Paul Petch.

Have you ever wondered what happens to your body physiologically when you run? As a teacher of Anatomy and Physiology at AUT University, I’m and happy to share this with you… in plain English!*

Why does my heart beat faster?
Your heart beats faster in response to the needs of your muscles during exercise. At rest or during low intensity activity most of our blood supply is directed towards our vital organs and in maintaining the processes that keep us alive. For example, blood flow is distributed to our digestive system to help us process the food that we eat. Blood carries oxygen and nutrients that our muscles, organs and cells need in order to work, It also carries waste and by products to our lungs and kidneys for excretion.

During vigorous exercise such as running, this blood flow is redistributed away from the gut and “non vital” processes to our large muscle groups, which are typically the ones that are working hardest. Our muscles require oxygen and glucose in order to create a molecule called Adenosine Triphosphate , or ATP.  ATP is  our muscular system’s energy currency. We must create and then spend ATP in order for our muscles to contract. The demand for oxygen and nutrients is why blood flow is diverted away from our other systems to “fuel the fire”, this explains why some regulatory processes slow down or halt until our body has finished exercising.

During vigorous exercise such as running, this blood flow is redistributed away from the gut and “non vital” processes to our large muscle groups, which are typically the ones that are working hardest.

Eating directly before exercising may be unwise as your muscles and digestive system are competing against each other for blood flow. This can result in a heavy stomach, or give you feelings of nausea or vomiting. This is dependent on what you eat prior to exercise as some foods will be processed through the digestive system quicker than others. Simple carbohydrates such as honey or energy gels for example will be processed a lot faster than a high protein food such as a steak.

Your heart beats faster in order to keep up with the muscles increased demands for oxygen and nutrients. The faster our heart beats, the quicker these nutrients will be delivered to the muscles.  Our stroke volume also increases. Stroke volume is the amount of blood that is pumped out of the heart with each beat. The combination of more blood being pumped and more heart beats per minute increases what is known as our cardiac output. Our cardiac output is the amount of blood that is pumped around the body every minute.

The more we train and the fitter we get , particularly when partaking in heavy cardiovascular exercise such as running, therefore the higher our cardiac output gets over time. Remember, the heart is a muscle as well,  and when we train it, it gets bigger and stronger. The bigger and stronger that it is the more blood it can hold and therefore the more blood it can pump with each beat. This is why those of us engaged in regular exercise will often have lower heat rates than people who are sedentary, our hearts are pump in a stronger and more efficient manner.

Why do I breathe so hard and fast?
This is for a very similar reason to why our heart beats faster.  As I mentioned previously, our working muscles need more oxygen in order to do their job properly. Our  needs to heart beats faster in order to be able to do this, but if we didn’t breathe any deeper or faster, there would not be enough oxygen in the blood to actually deliver! However this is not the only reason that we breathe more.

Our abdominal muscles help here as well. They are like our body’s natural weight belt, holding everything strong and in place.

Deeper and faster breathing is actually triggered by the levels of carbon dioxide, or CO2, in our blood. When our cells use energy they create this by product, carbon dioxide, which then needs to leave our muscles in our bloodstream. Our blood delivers the CO2 back up to the lungs for it to then be breathed out into the atmosphere. So the reasons for deeper breathing are two-fold – to get rid of CO2 and to retrieve more oxygen.

So what are my muscles actually doing?
This is a slightly more complicated one, but bear with me. We know that our muscles are able to create movement by contracting and pulling on our bones and joints. But just how they do this takes a little more understanding. The short answer is protein filaments that work together to shorten the muscle. The long answer is the sliding filament theory.  We have many types of proteins in our body that have many different roles. The two major proteins that are found in our muscles are actin and myosin. Actin and myosin essentially lie in strips in our muscles and overlap each other multiple times.

With the help of ATP the myosin protein filaments are able to hook on to the actin protein filaments and pull them closer together. When this happens many times in a row it causes the muscle to shorten. When a muscle shortens it pulls on a bone and causes shortening or lengthening of a joint angle which is obviously movement.

Many individual muscles and muscle groups are involved when we run and they all work together to create the action as a whole. To propel us forward our hamstrings must contract which straightens our hips and begins to bend the knee. The hamstrings keep working as our torso moves over and forward of our legs and our leg finishes the propelling phase.  Our two calf muscles are involved in this phase also. As we toe off our stride our soleus and gastrocnemius must contract to straighten, or plantar flex, your ankle. The calf muscles are quite powerful and help to give us spring when we run and also help to absorb some of the impact.

Our gluteal muscles assist in this phase also by helping to straighten the hips and pull the leg behind us. They also help to maintain our upright posture and stabilise our trunk as we run. Our abdominal muscles help here as well. They are like our body’s natural weight belt, holding everything strong and in place.

During the recovery phase of our stride our leg swings forward of our body ready to take another stride. To do this our hamstrings and calf muscles relax and the quadriceps muscles on the front of our thighs contract. This causes our knee to straighten and our hips to bend which brings our leg forward of our torso. The quadriceps also help to stabilise our knees and keep them tracking straight.

Many other muscles and groups are involved, contracting to keep our hips and knees stable and assisting the bigger muscles in moving our limbs.

How do my muscles know how and when to move?
Our muscles don’t simply just decide to contract and relax on their own. Our skeletal muscles do so under voluntary control from our brain. Our nerves carry messages from the motor cortex of our brain via chemical and electrical signals down to our muscles to tell them when to contract and how strongly.  You will notice that very young children are clumsy in their movements and as they practice their movements become stronger and more coordinated.  This is the work of our nervous system as it becomes more efficient in sending the signals and creates a memory for particular movements.

This is why it is often difficult to learn new movement patterns and alter things about our running stride as we get older.  In order to do this we need to recreate movement patterns and unlearn these old signals in order to replace them with new ones. In this case, practice really does make perfect!

Hopefully, this piece has given you a better understanding of what is happening with your body as you move or run,and maybe you will be able to start to feel these things as you do so. Happy running!

* I’ve got some basic knowledge of anatomy and physiology and understanding of what our body is doing when we run, but i’m not a doctor. If you have any concerns about your health or running, I recommend that you go see a specialist.

 

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Carolyn Arthur
A teacher of Anatomy and Physiology at AUT University and a NZ age-group triathlete. Started out as a runner and loves to be involved and inspire others to become active.
Carolyn Arthur

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About Carolyn Arthur

A teacher of Anatomy and Physiology at AUT University and a NZ age-group triathlete. Started out as a runner and loves to be involved and inspire others to become active.