Death by Exercise

I am going to deviate a little bit from my regular posts related to paramedicine.  This post is not entirely off from paramedicine since it does deal with the topic of physiology and applies to clinical populations such as people with heart disease, COPD, diabetes etc.  However, it does focus more on the aspect of exercise (the differences between aerobic and anaerobic) in relation to the load it places on the cardiovascular system.  I thought what I learned was really interesting and wanted to share it with you.  That being said, what I have written here is based on what I’ve learned in my university class.  As such, please do not read it and think that if you do have a heart condition you can jump in and do anaerobic exercises without harm.  I am not suggesting that.  It is always recommended to consult a physician before taking part in any exercise program.


Death by Exercise–Which is More Dangerous?  Anaerobic Activity or Aerobic Activity?

I’m taking an exercise prescription course right now, and we covered some interesting topics in class last week. We were talking about Death by Exercise. Which is safer? Aerobic activity (endurance activities like running, swimming etc) or Anaerobic activity (strength training/weight lifting etc.)?

Now here’s what I found really interesting: Anaerobic activity is safer than aerobic activity. Strange, I’ve always thought that it was the other away around.

So what is the reason behind this theory?

Well when we exercise, one of the biggest stressors involved is the rise of blood pressure (BP).

BP = Systolic (pressure of blood against your blood vessels when the heart pumps)
        Diastolic (pressure of blood against your blood vessels when the heart relaxes)

My capoeira grupo: Axé Capoeira at the Car Free Festival. Photo by PiscesDreamer.

During aerobic activity, there is a dramatic increase in systolic BP but no rise in diastolic BP. Meaning when the heart relaxes, there is no help in bringing the blood back to the body because of the low diastolic pressure. So this forces the heart to work harder; the heart has to pump blood not just TO your cells but it has to generate enough force to make sure the blood RETURNS BACK to the heart.  It is like pushing a table across a 10m room.  In one push you have to generate enough force to ensure it goes all the way across the room.  This puts immense stress on your cardiovascular system.

Okay, so what about anaerobic activity? Well anaerobic exercise causes a steeper rise in systolic BP than aerobic exercise, but unlike aerobic exercise, it also causes a dramatic increase in diastolic BP. This diastolic BP, or internal pressure, helps push the blood back to your heart every time the heart relaxes. In other words, it is a support system, therefore allowing the heart to actually rest and not strain as much during anaerobic exercise.  If we use the table analogy again, it’s like you pushing the table across the 10m room with one push, except this time you have helpers to assist you after your first push.  

In summary, it is because of the body’s self-help/protection mechanism that is the reason why anaerobic exercise is safer than aerobic exercises.  

Some of you may be wondering now, why most people who report of getting heart attacks are people doing anaerobic exercises like shoveling snow.  Yes, statistically speaking, more people get heart attacks or die from anaerobic exercise.  However, the glitch is that most of these people who die or get heart attacks from performing anaerobic exercises are people who are sedentary.  Sedentary people don’t do aerobic activities, else they wouldn’t be called sedentary, hence the low numbers of heart attacks during aerobic activities.  In other words, it is not because aerobic activity is safer than anaerobic activity that we see these high statistics of heart attacks, it is because these anaerobic activities are done by sedentary people whose bodies are not used to exercising.


Interestingly, during class, my prof also mentioned how holding your breath/valsalva maneuver (often used in anaerobic activities) serves as a safety mechanism with the increase in BP. It helps create an external counter pressure against the internal pressure built inside your blood vessels.

It was this last part that kind of puzzled me. I’ve always thought that the valsalva maneuver was bad for you. Or at least that was what I’ve been taught in all my other classes.  So I sent him an email:

Hi xxxxx,
I have a question.  Last wednesday we talked about aerobic and anaerobic exercise in regards to BP (differences between systolic and diastolic).  We discussed how anaerobic exercise is actually safer because of the “support system” provided by the increase diastolic pressure and counter pressure in the blood vessels from the outside by making use of breath holding/valsalva maneuver.  If this counter pressure is actually good as a protective mechanism then shouldn’t we utilize this breath holding maneuver more often as opposed to not using it?

However, I’ve been taught in previous classes that the valsalva maneuver is actually dangerous because it causes an abrupt rise in BP and when you release your breath, the blood rushes in to the heart causing an overload.  Or is this technique only not advised for certain populations like cardiac patients, whereas it’s okay for “healthy” individuals?

Here’s what my professor replied with:

Good question.  And I certainly don’t mean to suggest that holding your breath is a good thing.  But it’s not exactly a bad thing either.  Let me explain.

Jet pilots and astronauts experience tremendous amounts of force when they are in their plane.  The forces are so strong that they often feel light headed and are in danger of passing out.  To counter these extreme pressures they hold their breath – but just for a split second.  They repeat this pattern over and over – quick hold, then breath, quick hold, then breath.  What this does is counteract the external pressure by raising the internal pressure which in turn keeps them conscious in the cockpit.

The take home from this little ramble…………a split second breath hold is a good thing……..a long breath hold is not.  Holding your breath too long will have the same result (you’ll pass out).

When you do strength training blood pressure increases dramatically – both systolic and diastolic.  This means that the body is under a lot of stress.  Fortunately an exercise set or activity isn’t too long in duration.  In order to protect the body in the short term, breath holding (short little breath holds) creates enough counter pressure to prevent any damage from occurring.

Clinical populations certainly challenge the situation.  1) you definitely don’t want them holding their breath for a prolonged period of time because the body is already working under stress and 2) you don’t want them working at a level that is so intense the blood pressure will climb that dramatically.

I know I am talking around in circles and I hope this makes sense.  The summary in all of this is that all exercise has their inherent drawbacks.  Aerobic activity is challenging to the cardiovascular system because the heart has to carry all the effort with one push (which means we need to be cautious when we do aerobic activity).  Anaerobic activity is still safe because the heart gets help (but we still need to take precautions because you don’t want the exercise load to be too stressful).

So it seems that using short breath holds during anaerobic exercise can be protective for the healthy population.  As for the valsalva maneuver, cardiac patients and other clinical populations should always AVOID holding their breath while doing exercises because it causes undue stress on their heart and can lead to complications.


3 thoughts on “Death by Exercise

  1. Nice Valuable Post! Exercise for body to keep healthy, not for create trouble. Person must know about which type of exercise program is best for her/him & for that physician’s guideline is necessary.

  2. Good post. Was that class Hkin 469 with Paul Kennedy by any chance?

    Just wanted to add my two cents on the topic. As I understand, the heart plays an absolute minimal role in circulating blood through the veins back to the heart. Once blood passes through capillaries, the heart contracting does not produce enough pressure to keep it moving. It is actually a system of one-way valves and the squeezing effect produced by skeletal muscles that keeps venous blood circulating. That’s why when you lacerate an artery, blood will gush out with every heart beat, whereas if you lacerate a vein blood will pour out in a constant streaming flow unless a muscle squeezes the vein causing an increase in the flow.

    Hope that makes sense.

    1. Yes good point Eze. Just saying that the pressure plays a roll in returning blood. Also didn’t mention about muscle contractions in assisting the veins to “push” the blood back to the heart.

      And yes it was HKIN469.

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