CARDIAC ADAPTATIONS TO CHRONIC (PROLONGED) EXERCISE

PLEASE TAKE THIS KNOWLEDGE TO HEART!

Adaptations to chronic exercise are changes made to the structure and/or function of the body at the cellular, tissue, organ, and systemic levels, in light of long term exercise. In order for positive adaptations to occur, the body's cells, tissue, organ, and systems, must be challenged more than they have been before, according to the stimulus response principle.

As cardiac means "of the heart", this post will focus on changes to the structure and function of the human heart, post long term exercise. First, let us fine tune our focus on the two main goals of the heart - pumping blood to the lungs in order to enrich blood with oxygen and pumping oxygen enriched blood to the entire body.

The ultimate functional capacity of the heart is represented by cardiac output (L/min). Cardiac output is the mathematical outcome of multiplying stroke volume (mL) by heart rate (bpm). Cardiac output is very important as a representative of cardiac function. It directly determines oxygen and nutrient delivery, as well as disposal capacity.

Classic cardiac adaptations to chronic exercise include three major changes for the better: 1) Increased cardiac output; 2) Increased stroke volume; 3) Decreased heart rate. These three positive adaptations are the result of multiple processes improved as a result long term exercise, evermore so chronic aerobic exercise, than chronic anaerobic exercise (weightlifting).

Cardiac output is defined as the volume of blood pumped out of the left ventricle of the heart during one minute (60 seconds). Stroke volume is defined as the volume of blood pumped out of the left ventricle of the heart during one heart beat (or heart contraction; or mechanical cycle of the heart).

Maximal cardiac output is achieved when stroke volume and heart rate are maximized at the same time. The greatest cardiac efficiency is the result of the same cardiac output being achieved by the greatest stroke volume possible, and the lowest heart rate possible (see post about physiological capacities). Another way to examine cardiac efficiency is to pump out as much blood as possible compared to the volume of blood that was within to begin with (see post about ejection fraction).

An untrained person at rest (0% intensity) will have a cardiac output of about 5-6 L/min, while a well aerobically trained person will have a similar cardiac output at rest of about 5 - 6.5 L/min. Honestly, we do not expect a huge difference for this physiological measurement at rest, since both the untrained and the well aerobically trained are doing the minimal physiological work required to be alive.

An untrained person at rest (0% intensity) will have a stroke volume of about 70 mL, while a well aerobically trained person will have a resting stroke volume of about 125 mL. An untrained person at rest (0% intensity) will have a heart rate of about 72 bpm, while a well aerobically trained person will have a resting heart rate as low as 40 - 52 bpm.

An untrained person will have a maximal cardiac output (at 100% intensity) of about 25 L/min, while a well aerobically trained person will have a maximal cardiac output of about 38 - 41 L/min. An untrained person will have a maximal stroke volume of about 125 mL, while a well aerobically trained person will have a maximal stroke volume of about 210 mL. An untrained person will have a maximal heart rate of about 200 bpm, while a well aerobically trained person will utilize about 180 - 196 bpm (possibly less than their maximal heart rate).

I am repeatedly amazed by how a well aerobically trained person's stroke volume at rest (0% intensity), is the same as an untrained person's maximal stroke volume (at 100% intensity). I want you to imagine that both people are in the same room/space, only that the untrained person is running the fastest they can (aerobically) on a treadmill, while the well aerobically trained person is laying down and just breathing (rest; 0% intensity); Yet their stroke volume is the same. This is embarrassing to the untrained and equally amazing in favor of the well aerobically trained.

Now let us make the exact same comparisons between an untrained person, and a well anaerobically trained person. An untrained person at rest (0% intensity) will have a cardiac output of about 5-6 L/min, while a well anaerobically trained person will have a similar cardiac output at rest of about 5 - 6 L/min. Once more, we do not expect a huge difference for this physiological measurement at rest, since both the untrained and the well anaerobically trained are doing the minimal physiological work required to be alive.

An untrained person at rest (0% intensity) will have a stroke volume of about 70 mL, while a well anaerobically trained person will have a resting stroke volume of about 76 mL. An untrained person at rest (0% intensity) will have a heart rate of about 72 bpm, while a well anaerobically trained person will have a resting heart rate of about 66 bpm.

An untrained person will have a maximal cardiac output (at 100% intensity) of about 15 L/min even though they could produce a greater cardiac output under different circumstances, while a well anaerobically trained person will utilize a maximal cardiac output of only 18 L/min even though they could produce a greater cardiac output under different circumstances.

An untrained person will have a maximal stroke volume of about 75-80 mL, while a well anaerobically trained person will have a maximal stroke volume of about 90-100 mL. An untrained person will utilize a heart rate of about 190 bpm (possibly less than their maximal heart rate), while a well anaerobically trained person will utilize about 192 bpm (possibly less than their maximal heart rate).

During maximal weightlifting, the internal and external mechanical resistance/pressure on the heart and lungs might be so great, that attempting to produce the same maximal cardiac output as during maximal aerobic exercise, could end in disaster. Thus, we see lesser cardiac outputs for both untrained and well anaerobically trained during weightlifting.

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