How is it that I can go from not being able to run 3 miles to being able to complete a marathon?  What is going on during training that makes what used to be my hard speed during intervals my now normal pace?  Before I begin to explain some of the running physiology that occurs in our bodies during our training to make us better, faster runners I must first explain what an adaptive process is.  Our bodies are not in constant equilibrium.  There are continuous changes in our environment that our bodies must learn to adapt to.  Lucky for us, these reactions are hardwired into our DNA.  They are occur automatically without us needing thinking about them.

Stressors:

When is gets cold, our internal core temperature lowers.  This signals our vessels to constrict shutting off blood flow to our limbs to help maintain core temperature.  (That is why hands and feet get cold so fast.  Cold is a “stressor” or stimulus passively distorting our bodies’ normal equilibrium.  These stressors stimulate specific physiologic responses. An acute stress will stimulate a short term response usually in our central nervous system.  (Think heart rate increasing, blood pressure going up or down, sweat starting to pool)  Over time (think weeks to months) repeated or continuous stress will trigger organ function changes (think hormonal changes and process changes.  Did you know that 2-3 days at altitude will stimulate the kidneys to leave more CO2 in the bloodstream in response to continuous elevated breathing?  Remember it is increased CO2 that tells us to breathe faster not a lack of O2)  These organ functional changes lead to tissue and structural changes (also know as Genotypic Adaptation–you may have heard of Darwin, survival of the fittest)

Running Physiology, The Adaptations:

You may have heard that as we endurance train, one of the major adaptations that occurs in our bodies is that we build more mitochondria within our Type I (fatigue resistant highly oxidative muscle fibers.)  Mitochondria are little bacteria that have developed a symbiotic relationship with our bodies.  We keep these bacteria alive by our waste byproducts (they feed off of CO2) and they help us maintain long term exercise. (They are a major part of aerobic metabolism helping provide our working muscles with O2.)

One thing you may not know is that as we endurance train, we also increase our blood plasma volume.  Why does this help us?  It helps us because it allows us to maintain our cardiac output with a lower heart rate, meaning if we work to maintain our heart rate at the high level we are used to working at we will be running faster!

What is cardiac output?

Cardiac output (ml or L)= Stroke volume (ml/min) * Heart rate (beats/min)  …..We will return to this now let’s focus on what happens when our bodies endurance train.

Endurance training raises our core temperature.  Our bodies are dumb.  They don’t distinguish why core temperature raised, just that is elevated.  Therefore, heat stressors (a very hot day) and exercise have similar physiological responses.  (There are some added benefits that we get purely from exercise, however, training in a hot environment will have a greater effect on increasing one’s blood plasma volume.)

What does this all mean???

So why is this important?  Why will more blood plasma volume help me run?  First off, you may have realized running makes you sweat.  When you sweat you sweat out water from your blood plasma (you don’t sweat out the red blood cells which is why your sweat isn’t red!)  When this happens our blood becomes thicker leaving less of it to travel to our working muscles.  This makes our stroke volume lower (stroke volume is the amount of blood our hearts pump per beat) therefore to maintain cardiac output our hearts need to beat faster = tiring faster.  If we increase our blood plasma volume we will not only have a much larger stroke volume to start with, but we will also be able to maintain our stroke volume as we begin to sweat.  (You will also notice as we get into better shape we sweat faster.  This is because we have more fluid we can spare and we become more efficient at starting this process because our bodies are better attuned to responding tothe “stressor”.)

Wow that was a lot…trust me I don’t think I have had to explain that since I gave the lab presentation 4 years ago it was a mouthful!  So what do we take from this?  What are the best ways to improve your running physiology?

1.  Drink lots of water post workout.  If we don’t give the body water right away we will not take advantage of the physiological adaptations we will become dehydrated and the further we get away from our workout the less intense the rate of absorption becomes.

2.  Heat can stimulate the same effect.  It causes 40% of the response so sitting in the sauna, steam room, running in the heat, or even taking a hot yoga class can give physiological benefits to help your running.  But once again make sure you are properly hydrated!

3.  Sweat is good!  Sweat means our bodies are efficient at cooling themselves.  Sweat is your friend.  Especially if you have enough blood plasma volume to sweat a ton and pump oxygen to those muscles!

So when your tired, don’t skip that recovery workout.  Recovery workouts are a great way to remind your body to enhance it’s running physiology.  When you cross train, hit a hot yoga class.  The 90min in the hot room help leave you with more blood for your next run–If you rehydrate properly!