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Why does my heart rate go down as I get fitter?

Cardiac Output

I am often asked about the relationship between heart rate and fitness level, this very simple physiological reading can provide a good guide of of how fit an individual is.  On a basic level as a person gets increasingly cardiovascularly fit you would expect to see a reduction in their resting heart rate.

I am going to make an effort to explain the technical reasoning behind this relationship.  To fully understand how this works we need to grasp three main terms stroke volume, heart rate and cardiac output.

Stroke Volume

This is the amount of blood ejected from the left ventricle per contraction.  The average adult has a stroke volume of approximately 70-80 ml per contraction, where as in a more trained individual it can be as high as 100-110ml per contraction.  This increases with the level of activity you are engaged in  and can get as high as 200ml.

Heart Rate

This is the number of times that your heart beats per minute, in a healthy adult an average resting heart rate of 60-80 BPM (beats per minute) would be considered average. This can decrease to 35-50 BPM in more well trained individuals. As you exercise or increase the demands on the body this will increase, and over time with age your resting heart rate will increase year on year.

Cardiac Output

This is the amount of blood pumped out of the left ventricle into the aorta per minute.  This meas that it cn be worked out using a simple equation:-

Cardiac Output = Heart Rate x Stroke Volume

If we look at the average person with a stroke volume of 70ml and a heart rate of 75BPM at rest, so if we work this example through:-

Cardiac Output = 75 x 70 = 5,250ml/min (5.24L/min)

To answer your question

As you get fitter your heart becomes a more efficient pump as this happens your heart increases the amount of blood it can pump out per beat (stroke volume).  So to maintain a given cardiac output the heart does not have to beat as often, thus reducing the heart rate.

So in our example above, if our client increased their cardiovascular fitness levels and achieved a stroke volume of 80ml. This would correlate to an increased fitness level, to maintain the 5.24L/min that they require at rest their heart would only have to beat approx 66bpm as opposed to 75bpm that they needed in their less fit state.

Ultimately this reduction in use of the heart and increased efficiency means that there is less wear and tear on the heart itself and translates into reduced risk of a range of heart related conditions.

 

This entry was posted on Wednesday, May 14th, 2014 at 11:15 am and is filed under Articles. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.