The other day a friend pulled me aside to ask about heart rate training. He is in his mid 30’s and is mostly an ultra distance runner. “When I was running yesterday, I got my heart rate up to 201, is that possible? Should I use that number to figure out what heart rate zone I should be running in?”
He was confused because of the familiar maximum heart rate formula, “220-age=max HR.” This formula is ubiquitous in the fitness world and lay press, and is used to calculate the HR zones for training at different intensities. This training method is unreliable for a variety of reasons.
First let’s look at how this formula was derived, and what it means. Several years ago, a great review paper was published by Robergs and Landwehr that goes into great detail about the formula. Its first use was in a review article by Fox. In this article the authors evaluated heart rate data from a variety of studies in which people underwent a graded exercise test to determine their maximum heart rate. The studies all used different protocols for the graded exercise tests and the test subjects were of varying ages and health statuses (smokers, non-smokers, etc). The data points were plotted on a graph of age vs. maximum heart rate, and the line of best fit was described by the formula “220-age.”
In the many years since, there have been scores of other studies designed to create a heart rate prediction formula for various groups of people, including athletes, people with specific disease conditions, and people on specific medicines such as beta-blockers. The formulas all have a similar appearance, for example a fraction of age subtracted from a constant in the low 200 range. E.g. 207 -.7*age.
However in every single one of these studies, there is also a standard deviation of about 5-10 beats per minute. That means that for the fiftieth percentile group in the non-study population, the formula may hold true. But how do you know if you are in that group? The only hard fact that can be deduced from all of these studies is that there is generally a linear decline in maximum heart rate with age.
So the first problem that we have in trying to train based on maximum heart rate is that the maximum heart rate formula, while possible accurate for a group of like people, is most likely inaccurate for any given individual. HR variations of 5-10 bpm are so large that one person using the formula for endurance training zones may be getting an endurance workout, while another person of the same age and fitness level may be doing a lactate threshold workout.
So is it better to try and determine your own maximum heart rate by exerting yourself as hard as you can? Not really. There is a second major reason why training with maximum heart rate is also un-reliable for endurance athletes. Maximum heart rate is essentially fixed and un-trainable. It may be higher when performing an exercise like running than during an exercise like swimming to different patterns of muscle recruitment. But most importantly, the physiologic changes that your body undergoes during endurance training are independent of an individuals true maximum heart rate.
Trainable aspects of physiology on a cellular level include an increase in muscle fiber size, an increase in fiber recruitment, increased capillarization of muscles (which increases the oxygen delivery), and increased mitochondrial density (which enhances your body’s ability to utilize the oxygen). In addition, by training at the correct intensity in terms of how your body is metabolizing fuels and creating energy, the lactate threshold and maximum oxygen uptake can be improved as well as the amount of time one can exercise above lactate threshold. All of these adaptations are independent of an individual’s true maximum heart rate. But they do depend on training at just the right intensity depending on what type of adaptation the athlete is trying to achieve. The “right” intensity can only be determined with either field tests or laboratory tests to determine the appropriate physiologic thresholds which will not only vary for each individual, but also change as an individuals fitness improves. None of these tests involve the determination of maximum heart rate.
To summarize, there are two main reasons why maximum heart rate zones are inappropriate training zones for the endurance athlete. First, the inaccuracy inherent in a set formula to calculate the maximum heart rate is too great, and secondly your lactate threshold and maximum oxygen uptake will improve as your fitness improves. The static heart rate training zones determined by a maximum heart rate formula or test provides only a static set of ranges that will most likely be inappropriate to develop fitness for an endurance athlete, and will certainly be inappropriate as an athlete’s fitness level changes.
For more information about how to determine the proper training zones, see the article on Lactate threshold field testing. For a discussion of why lactate threshold testing is the best way to determine your training zones, read the article on lactate threshold and VO2 max – coming soon!
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