What should your pulse rate be?

Image attribution: "MF-180" by Pascal. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

Image attribution: “MF-180” by Pascal. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

The topic of the pulse rate is one that our patients and healthy athletes frequently like to discuss with us.

With the increased availability and ease of use of wearable monitors, the optimal exercise heart rate has become an almost universal subject of conversation, not only in the athletic community but also among those who are just embarking on an exercise program.

In general, athletes are interested in the pulse rate in 2 situations:  the resting pulse rate, best measured upon waking in the morning, and the pulse rate during sustained aerobic exercise, such as running or cycling.  Today we will address the pulse rate during exercise and leave the resting pulse rate for a separate article.

So what is the physiologic meaning of the exercise pulse rate?  Is there a pulse rate one should aim for?  What if the rate falls outside the target zone?  Can the pulse rate ever be a clue to a cardiovascular problem?  Let’s take these questions one by one.

1.  What is the pulse rate and what does it mean?

To review, the heart beats in order to distribute blood to all parts of the body according to needs.

With each heartbeat, a pressure wave form or pulse is initiated and travels from the heart down the arteries (red in the diagram below).

Image attribution: "Blutkreislauf". Licensed under CC BY-SA 2.5 via Wikimedia Commons.

Image attribution: “Blutkreislauf”. Licensed under CC BY-SA 2.5 via Wikimedia Commons.

Because certain arteries are close to the surface of the body, the pulse can be “palpated” with a couple of fingers placed gently at the spot.  For example, one can palpate the pulse as it travels past the carotid artery in the neck, as shown in the selfie below.

 

Carotid selfie

Image attribution: Selfie. All rights reserved. 🙂

Alternatively, you can check the pulse rate by palpating the radial artery in the wrist with the fingertips of the other hand. Roger Moore, a.k.a 007, can show you how to do it in this short YouTube video.

The pulse rate, then, is the number of pulses per minute.  The pulse rate is typically equal to the number of  heartbeats per minute (also known as heart rate) since every heartbeat generates a pulse.  There are exceptions  to this rule which we will address below.

As we saw above, each heartbeat tries to satisfy the oxygen and nutrient needs of the body, but the heart rate takes into account the efficiency of each heartbeat.  In other words, if the heartbeats distribute blood efficiently, then fewer heartbeats per minute are needed.  On the other hand, if the efficiency of the heartbeat is less, then more heartbeats per minute are needed, so the heart will compensate by beating faster.

This relationship between heartbeat efficiency and heart rate is the reason why athletes and trainers think of the pulse rate as a clue about the fitness of the cardiovascular system.  Athletes tend to have lower resting pulse rates and lower peak pulse rates when they are well conditioned than when they are out of shape—everything else being equal.

However, many factors besides cardiac fitness can influence your heart rate at any given time:  your age, your nutritional status, your sleep status, your stress level, genetic factors, anatomic factors, etc., all will affect both your body needs for circulation and the ability of your heart to meet them.  So remember, the pulse rate is just a clue, not the whole story about how fit you are.

2) What should my exercise pulse rate be?

The concept of a “training zone” or pulse rate range that one should aim for during exercise relies on some notions of exercise physiology, such as the maximal oxygen consumption and maximal heart rate.

If you exercise on a treadmill or stationary bicycle and gradually increase the intensity of effort, the oxygen needs of your body (and of your muscles in particular) will gradually increase.  As we saw, the cardiovascular system—as well as the lungs, the nervous system, the hormonal system, etc.—will kick in to address those needs.

Remember that the oxygen that you must bring to your muscles has to come from the surrounding air.  As a result of exercise, you “consume” more oxygen from the air.  After a certain point, however, the rate at which you consume the oxygen reaches a plateau beyond which it will not increase, even if you exert more effort.  This is called the maximal oxygen consumption and is abbreviated “VO2 max” in technical language.  If you exert yourself beyond that level, you will reach the point of exhaustion pretty quickly.

The VO2 max is a reliable measure of general fitness, i.e., of how efficiently the body adapts to the needs imposed by physical activity.  Athletes who train intensively will develop over time a greater ability to extract oxygen from the air and a higher VO2 max.  (Do not get too fixated on having a high VO2 max, however.  Many champions have values that are less than their competitors.  There is more to being an accomplished athlete that a high VO2 max.)

As we saw earlier, with increased effort the heart rate increases also to meet the growing demand for oxygen.  When VO2 max is reached, the heart rate at that level is referred to as the “maximal heart rate” or MHR.

Now, the term maximal heart rate is a bit misleading.  It sounds like a built-in limit to how fast the heart can contract.  That is not quite true because we know that we can artificially pace human hearts to much faster rates.  Also, in some disease conditions, the heart rate can be faster than one’s MHR.  The MHR simply indicates the heart rate which supports someone’s maximal effort.

Because exercising at maximal effort is not sustainable, athletes commonly aim to exercise at some level below maximal effort, as indicated by a percentage of the MHR.  Depending on the training goals selected, a “training zone” may be 50-75% of MHR or, for more intense workouts, 80-90% of MHR.

The practical problem, of course, is that there is no easy way to measure VO2 max, and therefore no easy way to know what one’s MHR is.  In order to measure the VO2 max, you have to breathe in and out of tubes hooked up to a “metabolic cart” that will analyze carefully the concentration of oxygen and carbon dioxide in each breath in order to derive the oxygen consumption and determine VO2 max and MHR.

Image attribution: Cosmed - Licensed under CC BY-SA 3.0 via Wikimedia Commons -

Image attribution: Cosmed – Licensed under CC BY-SA 3.0 via Wikimedia Commons –

To overcome this limitation, scholars have proposed formulas to estimate the MHR.  By studying a number of healthy subjects of different ages and measuring their VO2 max with a metabolic cart, the scientists could note the MHR for each person and plot it on a graph as a function of age.

From Tanaka et al. ref (1).

From Tanaka et al. ref (1).

The graph above is one derived by Tanaka and colleagues, and you can see a trend:  as people get older, the MHR tends to get lower.  By applying a mathematical technique, they could come up with a best fit “regression line” and a formula to go with it.

The formula obtained to estimate the MHR is shown for men and women.  For example, men would have to multiply the age by 0.72 and subtract that number from 209.6.  For a woman, one must subtract 0.68*age from 207.2.  In practice, most people use a simpler formula, MHR = 220 – age, which was proposed in the 1970’s and does not take gender into account.

Whether you use the older formula or the Tanaka formula,  the “scatter” around the regression line is quite wide.  The formulas give only a rough estimation and will frequently either over-estimate or underestimates the true MHR.

For example, a very fit 57-year-old male patient of mine recently had his VO2 max measured in a laboratory and his true MHR was 190, quite a bit higher than the estimate obtained from the common or Tanaka formulas (163 and 169 respectively)!

If you or your trainer wish to use the pulse rate to structure your training routine, consider having your VO2 max measured in an exercise physiology laboratory.

3) Can the pulse rate be a sign of heart disease?

Because there is a correlation between the fitness of the heart and the heart rate, the pulse rate can be a sign of a heart problem.

For example, if someone develops a cardiomyopathy, which is a weakening of the heart muscle, the heartbeat may not distribute blood as efficiently as it once did.  To compensate, the heart rate may increase to a higher value than it otherwise would reach, particularly during physical activity.

Abnormalities of the hearth rhythm (arrhythmias) can also cause the heart rate to be either too slow or too fast, or even irregular.  For example, atrial fibrillation is a condition that can affect endurance athletes, and it is manifested by an irregular pulse that can be either fast or slow.

Also, be aware that an irregularity of the pulse will not be identified as such by a typical heart rate monitor.  When the pulse rhythm is irregular, the actual readout from some types of monitor may not be accurate.  If you sense that your pulse is irregular, you should check it manually and count the pulses during a full minute for a more reliable measure of the pulse rate.

Finally, if the heart rate is very rapid or irregular, the pulse rate may not be the same as the heart rate, because not every heartbeat will be of sufficient strength to generate a pulse.  For example, if an arrhythmia causes a heart rate to be 200 or more, and some of those heartbeats are very inefficient, the pulse rate measured at the wrist may only be 120 or 130, or some fraction of the heart rate.

What is the take-home message from all this?

  • I would certainly advise you to learn how to check your pulse.  It is one of the vital signs, and if you feel unwell, it may be a good clue that something could be wrong with your heart.
  • The formulas to estimate the maximal heart rate to determine “training zones” are imprecise.  They should not be the only measure to guide your training intensity.
  • At times, an unusually fast or slow pulse could be a sign of a heart problem.  If in doubt, have it checked-out!

I hope you have found this article informative.  If you enjoy what we write, remember to sign up for our free monthly newsletter at the bottom of this page.  And from all of us here at Athletic Heart SF, we wish you many years of safe and enjoyable exercising!

 

Dr. Accad

 

References:

  1. Tanaka H, Monahan KD, Seals DR.  Age-predicted maximal heart rate revisited.  J Am Coll Cardiol. 2001 Jan;37(1):153-6