UNTRAINED VS WORLD CHAMPION
At rest, during exercise, and maximal exercise, cardiac output is regulated to meet the oxygen and nutrients needs of the cells. Cardiac output is achieved by stroke volume and heart rate multiplied, where heart rate reacts to stroke volume as its compensator. This means that heart rate changes according to changes in stroke volume, in order to achieve the cardiac output adequate for the metabolic demands of skeletal muscles and other active tissue/organs.
Rest is defined as 0% intensity while maximal exercise is defined as 100% intensity. Anything in between is by definition sub-maximal exercise. Cardiac output increases in a linear way from rest to maximal exercise, in an almost perfect 1:1 ratio with the demand for oxygen. We also know that every 1,000 mL of blood carry 201 mL of oxygen under normal conditions.
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In an untrained person, cardiac output increases from 5-6 L/min at rest to about 25 L/min at maximal exercise. Stroke volume increases between rest and about 40-50% intensity, then reaching its maximal volume. Within the same range of intensity, heart rate is also increasing.
Between 40-50% intensity and about 85% intensity, stroke volume remains maximal, while heart rate continues to increase at a slightly steeper pace than before, to achieve a growing cardiac output; Heart rate is compensating for stroke volume's inability to increase anymore, since cardiac output must continue to increase.
Between 85-100% heart rate is accelerated even more in order to supply oxygen ever faster in order to prevent lactic acid creation as much as possible. Yet, the faster the heart beats, the lesser time is left to fill up the ventricles with blood, causing stroke volume to decrease. This represents the need to decrease cardiac efficiency by increasing heart rate and decreasing stroke volume in order to prevent excessive lactic acid via the "pyruvate junction".
In an aerobically trained world champion, cardiac output increases from 6-6.5 L/min at rest to about 38.5 L/min at maximal exercise. Stroke volume increases between rest and maximal intensity in three different paces; pace 1 is between 0-40% intensity, pace 2 is between 40-85% intensity, and pace 3 is between 85-100% intensity. Contrary to the untrained, a world champion's stroke volume constantly increase never decreasing cardiac efficiency.
In an aerobically trained world champion, heart rate increases in a similar fashion to that of the untrained described above, with the exception that the well-trained can achieve maximal cardiac output with few beat per minute as their maximal heart rate. The untrained person's stroke volume increases from about 70 mL at rest to about 125 mL at maximum exercise, while the world champion's stroke volume increases from 125 mL at rest to 210 mL at maximal exercise.
The untrained person's heart rate increases from 72 bpm at rest to about 200 bpm at maximal exercise, while the world champion's heart rate increases from about 40-45 bpm at rest to about 195-196 bpm at maximal exercise.
Graph one: changes to cardiac output, stroke volume, and heart rate from rest to maximal exercise in the untrained.
Graph two: changes to cardiac output, stroke volume, and heart rate from rest to maximal exercise in the well aerobically trained
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