Why people with the same effort have different heart rates

A question that I have been asked many times before is why 2 people with the same body type and weight may have varying heart rates with the same amount of exertion.

The body is an amazing thing, and it adapts in so many ways. Our hearts for example have to pump the same amount of blood volume through the body based on the exertion that is required. Along with many other things, the blood carries into the bodies the necessary nutrients and oxygen, and carries out the by-products of muscle contractions including the lactic acid.

So, how can a trained athlete have such a lower heart rate than an untrained athlete given that they are doing nearly the same thing at the same level of exertion and the body having to pump the same amount of blood? The answer lies deep in the heart muscle itself.

As a untrained person starts to do consistent exercise the heart muscle begins to adapt to the demands that are being placed upon it. Just like any muscle in the body, with regular exercise the heart starts to adapt to the stress placed upon it. The heart becomes more adapt to handle the challenges placed upon it and becomes more efficient.

What physically happens is that the interior of the heart chambers start to expand and enlarge. The overall size of the heart stays the same, but each of the 4 chambers actually expand to accommodate more blood. As the heart pumps, with each contraction the amount of blood that is pulled into the heart and is pumped out is increased. So, suddenly with each heart beat the volume of blood being moved through the heart is increased with each beat. Therefore, if an equivalent amount of blood needs to be moved throughout the body, then the number of beats required for a trained athlete is less to pump the same amount of blood as a untrained athlete who has a heart that isn’t pumping as much blood per beat.

How long does this take to change the effects and the amount of blood pumped through the heart depends on the time spent, but generally it is said that an initial adaption period is 8-12 weeks of consistent 120-140 beats per minute training 8-12 hours a week. Of course, for some it will be less and for others it will be more. To get the most out of the time necessary to train and adapt to this much time on the bike, it is best that the cyclist do this during the winter base period.

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