While power training may be all the rage, the high tech toy of choice for the majority of cyclists is the heart rate monitor. One important question to ask is exactly at what heart rate should one be working at to optimize training time and efficiency? The first thing to understand is the different ways by which scientists and coaches base their heart rate training zones. It is indisputable that heart rate monitoring remains the dominant mode of fitness monitoring for the majority of cyclists. Ever since Francesco Moser pioneered the use of heart rate monitors (HRMs) to closely track his preparations for the Hour Record in 1984, HRMs have become almost as ubiquitous as a water bottle for both elite and everyday cyclists alike. The cardiovascular system is a complex interplay of many things going on inside your body, but heart rate remains the simplest indicator of strain on the entire cardiovascular. Cardiovascular Physiology 101 Cardiac output is simply the overall volume of blood that is being pumped out of your heart each minute, with maximal cardiac output estimates of 25 L/min for untrained individuals and possibly 35+ L/min for highly aerobically fit athletes. In turn, cardiac output is simply your heart rate multiplied by your stroke volume, or how much blood is pumped by your heart with each beat. While cardiac output is ultimately the measure we would really like to have as a measure of training intensity. However, this is not common because, while heart rate is simple to measure using either a heart rate monitor or simply counting your pulse with a stopwatch, it is much harder to measure stroke volume. There are some non-invasive and some highly invasive methods, but they are generally done only in an exercise physiology laboratory like mine. Therefore, heart rate is what we use for tracking exercise intensity much of the time, but it is not perfect. Heart rate is also affected by your nervous system, as can be seen when you are at the start line of a bicycle race and your heart rate is already at 150 bpm before the starting gun even goes off! Or you could be tired and pushing yourself harder than ever, yet your heart rate will only reach 160 bpm as compared to your normal 175 bpm at threshold. In both cases, your nervous system is sending signals to your heart that overrides your body’s physiological demands for cardiac output. Maximal Heart Rate How best to use heart rate then? There have been numerous attempts to peg the ideal heart rate at which to exercise in order to maximize training efficiency. Some point to an idea of basing things on maximal heart rate, such as training zones set as particular percentage of maximal heart rate. For example, endurance efforts might be at 60-75% of maximal heart rate, tempo efforts at 75-82%, etc. For these zones to work, the critical assumption is that you have an accurate knowledge of your maximal heart rate. If you have been in a gym, then you have likely seen the most common way for determining maximal heart rate, and that is by subtracting your age from 220. However, as Matt McNamara wrote last week, there is little actual scientific backing for the concept of a maximal heart rate based on an equation of 220 – age. Here is an example from my own cycling career on the dangers of basing maximal heart rate, or indeed overall training, on a generic template. In my early years of competitive cycling, when I was an undergraduate in my late teens, my maximal heart rate should have been around 220-20, or 200 beats per minute. However, in all the tests I did on myself in the lab and on the bike, my heart rate NEVER exceeded 175 beats per minute, and often was much lower. Flash forward to when I was 23 and was on a regional development team. We would be climbing and I would be at 165 beats per minute while my partner riding right beside me was at 185 beats per minute, with both of us working at about the same overall exertion level. This was good evidence that heart rate by itself is not a valid point of comparison between cyclists. Another example from that time. Our coach would prescribe intervals where our heart rates should be about 180 beats per minute. However, there was no way I could do anywhere close to that, to which his response was simply that I should work harder. Not surprisingly, it was about that time that my personal interest in sport science got even deeper! How has my maximal heart rate changed, if at all, in the twenty years since? According to the 220 – age equation, my maximal heart rate should actually now be at 220 – 42 or 178 beats per minute. However, in all my lab and field testing, I cannot find a maximal heart rate above 165 beats per minute in the past four years. So let’s use me exercising at 70% as an example. • My twenty-something training HR would be 70% * 175 = 123 beats per minute. • My current training HR would be 70% * 165 = 116 beats per minute. Heart Rate Reserve Another way of quantifying heart rate training intensity is to base it on your “heart rate reserve” or HRR. Your HRR is calculated from both your maximal and your resting heart rate. As an example, your HRR might be 175 (maximal heart rate) – 55 (resting heart rate) = 120. Your exercise intensity might then be described as 50% HRR for an endurance effort. So using the above values as an example, this would be: baseline HR + 50%HRR, or 55 + (50%)(175-55) 55 + (50%)(120) 55 + 60 = 115 beats per minute. The advantage of the HRR concept is that it integrates both your minimum and maximum heart rate values, rather than simply your maximum heart rate. For example, you may have two cyclists with the same maximum heart rate of 175 beats per minute. But if Cyclist A and B have resting heart rates of 50 versus 75 beats per minute, this intuitively should make sense that the two cyclists might need different heart rate levels to achieve a particular training intensities. Using my example again, let’s figure out 70% training targets. My resting HR has not really changed in twenty years, staying at 50 beats per minute: • My twentysomething value = 50 + (70%)(175-50) = 138 beats per minute. • My current value = 50 + (70%)(165-50) = 131 beats per minute. Steady State Heart Rate A third way to normalize heart rate training levels is to anchor heart rates based on the average values that you might achieve during a 20-30 min time trial. Those of you training with power may see that this is very analogous to the 20 min test for functional threshold power. This is based on the idea that, this is the “maximal” heart rate you can realistically sustain for a prolonged hard effort, and therefore forms the best anchor for your training levels. In my case, this threshold heart rate really has not changed at all in >20 years of riding, racing, and testing. Despite my maximal heart rate decreasing by 10 beats per minute, and my functional threshold power changing over the course of a season and through the years, my threshold heart rate over a 20 min time trial or test has remained essentially constant at 155 beats per minute. In this case, my 70% training level in both my twenties and now would be: 70% * 155 = 109 beats per minute. Summary The critical lessons? 1. Do not rely on average values or estimates. Base things on your own values! 2. There is never a case of “highest/lowest heart rate wins!” All testing and training should be individualized, and the value of your data comes when you track your own training long-term. 3. I used a set “70%” to illustrate that different ways of anchoring your heart rate will get you different heart rate values. Of course, it is not automatic that a 70% is meant to represent the same training intensity (e.g. endurance) for each method! We will explore the concept of what might be an optimal heart rate training intensity in my next Toolbox. 4. You will likely need to change your heart rate training levels over the course of a season, or as you age. We will also explore this concept more in my next Toolbox. Ride safe and have fun
