Why heart rate matters

For decades, monitoring and analyzing heart rate (HR) stood as a key tool for training program development and control, as well as competition feed back. Unfortunately, HR has fallen out of favor is recent years as the use of power meters and GPS watches has grown. In some respects this was to be expected, because these devices allow for more precise measurement of intensity and ultimately output. However, some coaches have labelled HR as irrelevant and useless to training or racing. Such opinions are not only incorrect, but they only highlight the lack of fundamental physiological understanding some “experts” have; in truth, it is likely as much about selling their books, services and other products, as it is misunderstanding. In this article, I will layout some of the best ways to utilize HR both by itself, as well as in conjunction with perceived exertion and output meters.

Heart rate, more than just beats per minute

Some common arguments against HR are that it responds to slowly to external work, like sprints, or is too variable and impacted too much by external factors. OK, yes, HR is not a great measure of specific intensity, but it is a supreme measure of stress and a good estimate of oxygen consumption. Moreover, the fact that external and internal factors affect it means it can be helpful in metering your efforts. Case in point, if its super hot out and your HR is 10 beats higher than normal that’s telling you something important and shouldn’t be discounted because your zone says you need to train at a specific HR. Actually, the use of zones have, at times, been to the convenience of lazy or unoriginal coaches, and detriment of their athletes (I’ll cover Zones in an upcoming post).

I (too) often hear athletes proclaim that they cannot use HR because it just fluctuates too much. Really?! First, let’s thank Odin that in his wisdom he created a cardiovascular system that is as responsive as mammalian physiology. Moreover, variability in HR is actually a good thing (see HRV). In my experience, HR does NOT fluctuate much more than 5 beats at a steady effort; if it does either you’re not pacing well, your monitor is getting interference, or you are suffering from an arrhythmia (call 911 on the last). Frankly, when I’m balls to the wall, eyes bleeding, maxed out in a race my HR is either stable or dropping as I fatigue and slow down. If its slowly dropping in training try harder or consider you’re fatigued and need to cut it short. Either way, the feedback you’re getting is useful.

HR Training Tip #1: Stop being lazy yourself and actually TUNE-IN when you’re training to understand what your HR is and when it changes, what is going on around you. Allen Lim has lamented that with the advent of new tech in cycling he is spending more time teaching young athletes how to rate their exertion (RPE) than how to look at their power file. We’ve spent way too much time talking about burning matches and TSS points, than we have about how to train f#$&ing hard and what it should feel like, or not!

My motto for HR & RPE

HR Drift

Another argument against HR is the upward drift phenomenon reported during prolonged exercise. It is beyond the scope of this article to delve into HR drift in depth, but here’s the general overview:

The typical person has 5 L of blood. Blood is how oxygen is delivered to the muscles, as well as how the body is cooled (see our hydration posts). In order to deliver blood your heart pumps a certain amount of blood with each beat (stroke volume) , and beats a certain number of time each minute (HR).

As you work harder, more blood flows to the muscles, BUT, the harder you work, the more heat your muscles produce. Hence, the harder you work, the greater the need for cooling capacity. In order to increase cooling, more blood must flow to the skin where sweat evaporates and carries away heat, but also carries away water, making rehydration important. In theory, if you lose more water your total blood volume (made up of 50-60% water) and reduces the total amount of fluid that can deliver oxygen and/or cool the body. Normally, we would say that either more blood goes to the skin to cool, so you slow down (fatigue). However, an alternative, albeit for a limited time, is to maintain blood flow by pumping it faster (ie, higher HR). So there you have it; in order to maintain a certain pace/power with less blood and/or increasing body temperature you’re HR drifts upward.

The above scenario is what we’ve seen in published literature for lab studies. However, real world field data do not always support this. In 2006, Ericsson reported that among racing cyclists during a broad range of competitions up to 4 hrs, HR drift was typically only about 5 bts. Without getting into all the complexities of hydration, the likely reason was the high degree of cooling offered by cycling; lots of air flow means lots of convective and evaporative heat loss. In my personal experience, I’ve seen little change in body temp (max under 102 d F) during road cycling and usually MTBing, as well as HR drift. During running, however, I have seen an exponential increase in temperature as I exceed the pace where HR is 155 bpm. Put another way, I don’t see HR drift in running as much as I seen rapid increase in body temp. This makes sense considering cooling rates are much higher during cycling at any given workload; actually, they are possibly exponential with greater cooling as speed increases.

HR Training Tip #2: HR drift is NOT a good reason to discard HR data. On the contrary, paying attention to HR (which is closely linked to oxygen consumption/metabolic rate) can help you develop better training and race pacing strategies. In my own experience, I can run for hours at a HR under 150 even in the hottest weather. If my pace is even and I’m at least drinking something, I don’t see drift. However, above 155 I know my run time is progressively shorter; I can typically only run 45 min or less above 170 bpm in 95+ d full sun exposure. This knowledge helps me plan my pacing for races too!

For runners, I suggest using HR thresholds to determine when and how long to walk, so when your HR pops over, walk until it drops 5 beats below then run again. This gets you responding to what your body’s response is, not what you perceive is most comfortable. For example, if you find yourself uncomfortable on runs (at any pace) and you feel like walking look at your HR, if that’s where it normally is for that pace, either avoid walking, or again, let it drop 5 beats below, rather than when you feel better. Getting faster doesn’t usually mean feeling better, but usually feeling the same at the same relative intensity (that is actually faster).

HR Training Tip #3: Recovery HR’s provide critical feedback on your adaptations. Monitoring HR following exercise provides a wealth of knowledge. I use it most effectively for running and swim intervals, and it can be useful in working past the excessive rest periods many use because training is uncomfortable.

Many people discount HR because of the lag time between actual effort and HR response. I’ll be the first to say that basing short intervals or sprints off of HR can be useless IF you’re using long rest periods, but if your rests are short, time to peak HR can be useful. Even more important, however, is how much HR drops in 60 sec. For unhealthy individuals, a HR drop of less than 12 beats in 1 min following maximal exercise is associated with a major risk for sudden death. For athletes, though, 1 min HR recovery (HRR) can be an excellent gauge for interval recovery or overall training recovery.

In a 2009 paper, Lamberts et al. found that HRR improved significantly after 4 weeks of interval training, making it a useful non-invasive measure for monitoring performance. Subsequent work has shown that an decrease in HRR (ie, less of a drop) after an interval can be indicative of overtraining. For example, if your HRR is normally 40 bts and in week three you’re now at 35 or 30, its probably best to call it a day and add some more recovery. AN even more promising tool involves monitoring morning HR variability (HRV). HRV is available from a number of devices now, particularly Polar, and measures the beat to beat difference. The lower your HR and GREATER your HRV, indicates better recovery. Why? Because HRV is dictated by the sympathetic (SNS) and parasympathetic nervous systems (PNS); your more beat to beat difference indicates less resting SNS input and better overall heart health. Low HRV is also indicative of higher mortality in unhealthy individuals. While clear standards are hard to come by, finding your own baseline can give you great insight on how to modify your day-to-day training.

Hopefully I’ve changed a few minds on how HR can and should be incorporated into training, particularly runners. As with any training tool, it is only one perspective that will help guide you. Please let me know how you use HR and what you’ve learned from it!


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2 Comments to “Why heart rate matters”

  1. Chris Aarhus says:

    Glad to see someone write about this..I hadn’t got around to it yet lol. But I couldn’t agree more. Being a cyclist then into triathlon, I’ve used hr for past 20 years. I don’t even use it to the extent you have here. I disliked how everyone seemed to trend to discounting it’s use and like the reasons you gave above, are simply sighting variables they didn’t try to understand.
    I too have to teach people how to read their bodies better because they are so married to the data. They don’t understand that if running the same 8min mile is done 5-10 beats less may give them some confidence in what they are doing is working. Also, I have seen people clearly outside the objective of the ‘ prescribed workout’ of watts or pace, without a concept of what it should ‘feel’ like.

    • Tradewind says:

      Great points Chris. You may want to still write that article, because it’ll be relevant for release 5 years from now too! As I said in the article, the arguments against HR mostly make no sense. If our HR was so variable during exercise how would we effectively regulate blood flow during exercise. Is it ideal for measuring intensity? Probably not. But it is a great tool when used appropriately. I think power is actually an easy learn, so people get a little knowledge and stare at their computer all day.