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Why you should use a heart rate monitor for exercise

photo of man running

I’ve always been into nasty exercise. Not just the kind you get through doing sports you enjoy, but the gruelling sessions sprinting up hills, and the long runs on freezing cold mornings. To be clear, I haven’t enjoyed a lot of these sessions, but I’ve done them anyway because, well, you need to exercise, don’t you? And the more it hurts, the better, right?

Until a couple of years ago, my rough cardiovascular ‘routine’ was to do three sessions a week of as much intensity I could muster at the time. I’d dread each session, knowing that even if I’d tricked myself by saying I’d just do a gentle run, I’d end up speeding up. I’d then feel good for all of two minutes at the end, before failing to give myself enough recovery for the next session. And repeat. This all changed when I first got a heart rate monitor.

Heart rate monitors are not just for professionals

Heart rate monitors used to be mainly for professional athletes, but accurate models are now much more affordable. I bought a Polar H10 for £64 ($78) in 2019. For me, this has been the best single investment I’ve ever made in my personal fitness. So far, it’s worked out at about 23p ($0.33) per workout, and I haven’t even had to change the battery.

How heart rate training works

The basic idea of heart rate-based training is that between your maximum and resting heart rates are a number of ‘zones’, which roughly correspond to the effort you’re putting in. Exercising within the different zones gives you different benefits. Lower heart rate is for recovery and building endurance, whereas training above your ‘lactate threshold’ improves your ability to sustain high-intensity exercise for longer.

Different apps and coaches split these zones differently, but it’s the principle behind breaking it down this way that’s important. Depending on what you’re training for, you will want to apportion your exercise time accordingly. For example, a marathon runner will spend more time training endurance, whereas a 1500m runner will do more high-intensity sessions.

Of course, not all of us are training for a specific event. But like it or not, we do all need to do some cardiovascular exercise to live long, healthy, happy lives. Both the US CDC and the UK’s NHS recommend getting at least 150 minutes of moderate-intensity aerobic exercise every week. They also say that you can decrease your time spent exercising, if you up the intensity – down to as little as 75 minutes of vigorous (or ‘very vigorous’) exercise. In other words, the exercise you should do is a combination of three factors:

Frequency    x    Duration    x    Intensity

The problem with this is that whilst it’s easy to measure the frequency and duration of your exercise, getting the intensity right is more difficult. And that’s where a heart rate monitor comes in.

Getting the right intensity level

Your heart rate is a good approximation of how hard you’re working in a given workout, although it’s important to note that it can also be affected by things like caffeine intake, sleep, stress, hydration, and altitude. In other words, it serves as a good proxy for the intensity level of our workouts – allowing us to manage the third key factor in even the most basic exercise regime. Without being able to measure intensity, we can’t properly manage it.

The government recommendations do give some examples of what counts as ‘moderate’ or ‘vigorous’ exercise, but these don’t account for how intensely each of us does the activities. One person’s easy jog would be a lung-bursting effort for another person. In other words, they’re a measure of the activity, rather than the outcome. But by measuring the stress on our hearts caused by exercise, we have a much clearer indication of whether we’re getting the required raise in heart rate.

Of course, we could just ensure that we’re each doing 75 minutes a week of the most vigorous exercise possible, but unless you’re a professional athlete, that’s unrealistic. More likely is overtraining, burnout, and plateauing: my home for approximately 20 years. A sustainable method will involve a mix of really intense exercise, steady-state training that builds endurance, and easier recovery sessions. If you play a particular sport, or have a certain lifestyle, then training more specifically for that can have greater benefits that simply doing whatever exercise you’ve always done.

How I use a heart rate monitor

Since using mine, I’ve been able to manage my intensity much more effectively, ensuring I’m getting a mix of low, medium and high-intensity workouts, rather than putting my body into a regular state of near-collapse. Now, I can’t tell you this has been responsible for me breaking the two hour barrier for the marathon, but that isn’t the point. The point is that since breaking down my exercise by heart rate, I’ve been incredibly consistent. I’ve had fewer injuries, fewer sessions missed through lack of will, and most of all, a much more enjoyable experience. Overall, I’m getting a much better return for the level of effort I’m expending.

Each week I break my cardio down into three sessions:

  • one 30 minute high-intensity session, where my heart rate is in ‘zone 5’ for at least 5 minutes
  • one medium-intensity session where my heart rate is in ‘zone 3’ for at least 20 minutes, and ‘zone 4’ for at least 20 minutes
  • one low-intensity session where my heart rate is in ‘zone 2’ for at least 60 minutes

For me, this split means I easily hit the 150 minutes of moderate-intensity-equivalent exercise over the week. And if you don’t want to structure your exercise around the different zones, at least tracking your heart rate during it can give you a clearer picture of how hard you’ve worked, and what you have left to do that week.

Alternatives to heart rate training

Competitive athletes will argue about the benefits of heart-rate training, versus training by power, training by pace, or training by feel. Some of that is down to personal preference, but it also depends on whether you care about output, outcome, or perceived intensity, respectively. Most people tracking those metrics will want to keep an eye on their heart rate too.

However, for most people doing exercise to be healthy and happy, what really matters is actual intensity, for which heart rate is the best proxy. You could leave that to a rough guess about how hard you’re working, but for something as important as exercise, it’s best not to leave it to chance.


Appendix

It’s important to note that there are limitations to HR monitors, and to measuring heart rate generally. Firstly, some monitors, particularly optical ones of the kind you usually find in watches, can be inaccurate as they’re affected by how tight the watch is, whether there’s any dirt or grease on the watch, and excess moisture on the skin.

Secondly, if you don’t have an accurate measure of your maximum heart rate, then your heart rate ‘zones’ will be off. Laboratory tests to find your maximum can be expensive, and the commonly-used formula of 220-your age fails to account for a whole myriad of important factors. To work these out, I’d suggest doing a ‘field test’ of the kind described here. It will be a lot of effort, but well worth it in the long run.

Thirdly, as I noted above, factors other than how hard you’re working can affect your readings, such as caffeine intake and stress levels. This isn’t too much of a problem for our purposes, as we’re interested in how hard out heart is actually working, rather than how hard it should be working for a given effort.

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