Are You Keeping Track? How to Best Use Your Physical Activity Tracker

Why use an activity tracker?

One of the most powerful predictors for being active is whether or not you are self-monitoring how active you are (1,2). Most people have a vague idea of how active they are, but this tends to be pretty inaccurate most of the time.

You can self-monitor without an activity tracker by using pen and paper to keep track of every activity you do from the morning to the evening. But this method is labour intensive and hard to keep up in the long run. More importantly, this old-school form of self-monitoring doesn’t even come close to the precision activity trackers offer.

By tracking steps or ‘activity minutes’ (named ‘Active Zone Minutes’ for Fitbit, and ‘Intensity Minutes’ for Garmin) you will be provided with an accurate measure of whether or not you are meeting the physical activity health guidelines (i.e., 150 minutes of moderate to vigorous physical activity per week) (3). It will also allow you to keep an eye on your personal activity goals, and to view your progress over time. All this would be very difficult without an activity tracker. Extra bonus: research has shown that the most popular brands of activity trackers (e.g., Fitbit, Garmin, Apple Watch) are very reliable when it comes to tracking relatively simple measures such as ‘activity minutes’ and especially steps (4). Activity trackers are also much better than smartphones in tracking physical activity and steps.

But wait, there’s more…so much more!

Today many activity trackers track a plethora of other measures their manufacturers promote as important to keep track of your health and fitness. Though, is that really so? Measures such as your resting heart rate, your heart rate during exercise, maximal heart rate, and your VO₂max. Should you keep track of those variables? Let’s have a look.

Resting heart rate

This is your heart rate at rest, when you haven’t been doing any activity for a while, and when you’re awake. The normal resting heart rate range is between 60 and 100 beats per minute, though generally a lower resting heart rate is a sign of good health. There is strong evidence indicating that your risk of dying of any cause (all-cause mortality) is much lower when your resting heart rate is low (e.g., 40 beats per minute) compared to when it is high (e.g., 100 beats per minute) (5). Your resting heart rate will gradually go down as you become fitter from doing a lot of physical activity, especially higher intensity exercise. Activity trackers are pretty good at tracking this, but you can also measure your resting heart rate by monitoring your pulse and using a stopwatch.

Heart rate during exercise

Activity trackers will also measure your heart rate when you’re active. Whether it’s good or bad is much harder to interpret, as it will go up and down in response to how hard you’re working out. It’s easy to overrate the importance of your heart rate during activity. The most important thing is that you’re being active, no matter you heart rate (6). However, if you want improve your fitness efficiently, and stick to the exercise training principles like professional athletes do, then you will want to know your heart rate during activity. There are five heart rate zones, and ‘Zone 5’ is exercising as hard as you could possibly go for no longer than 30 seconds or so. For regular exercise, the aim is to have your heart rate in ‘Zone 2’ most of the time. When you’re in Zone 2, your heart rate, sweating, and breathing are all up. You could probably still say a few words, but having a conversation would be difficult. Activity trackers are not bad for indicating what Zone you are in. But a dedicated heart rate monitor with a strap around your chest will do a much better job in measuring your actual heart rate (7). Though if you just want to be more active and healthier, without a specific training goal in mind, you can exercise at a level that feels good to you and not worry about the Zone you’re in, you will be OK.

Maximal heart rate

This is the hardest your heart could beat when you’re active in Zone 5, not something you could sustain very long. Your theoretical maximal heart rate is 220 minus your age ± 20 (to account for genetics). Your maximal heart rate is not influenced by how much exercise you do, or your fitness level. Moreover, activity trackers have a reputation for not measuring it accurately (8), so you may as well forget about this one.

VO₂max

VO₂max is another measure of fitness that correlates well with all-cause mortality. The fitter you are, the lower your all-cause mortality (9). It is the volume (V) of oxygen (O₂) we could breathe maximally (max) over a 1-minute interval (usually expressed as millilitres of oxygen per kilogram of body weight per minute: ml/kg/min). Your muscles need oxygen to work, hence the more oxygen your body can process, the harder you can work, thus the fitter you are. Usually this is measured in a lab on a treadmill or exercise bike while wearing a mask that measures how much oxygen you’re breathing in. The exercise level is increased until you can’t go any harder, at which point the VO₂max is measured.

Activity trackers that provide you a VO₂max value obtain it very differently. Activity trackers look at how fast you are running using a GPS-chip to measure your speed. They then take your heart rate and compare both these measures to values from other people of your age and gender. For example, if you run fast with a low heart rate (for your age/gender), your tracker will assume you could go even faster and are therefore relatively fit, resulting in a high VO₂max. These estimates are not very accurate as they are based on lots of assumptions (e.g., accuracy of GPS and heart rate monitor, your body shape and size, running on easy/hard terrain) (10,11). However, there’s one good thing about them, the error of the measurement is reasonably consistent. This means that the number itself might not be reliable, but the direction in which the number changes is. Or in other words: if the VO₂max measured by your activity tracker is gradually increasing it probably does mean you are getting fitter. In many ways the VO₂max is comparable to your resting heart rate, only the latter goes down to indicate you are getting fitter.

What should I remember from all this?

Focus on how many steps you take every day or the number of ‘activity minutes’ you achieve! Even a basic activity tracker (or pedometer) will accurately provide these measures (12). If you are regularly active over a long period of time this will gradually improve your fitness, resting heart rate and VO₂max. But there is no real need to track these measures and pay more for an activity tracker that records them. Don’t worry too much about your heart rate during exercise and forget about your maximal heart rate.

If this is steps per day, great! If this is an increasing VO₂max, by all means go for it!

Finally, let’s not forget that a large amount of research overwhelmingly demonstrates the health benefits of being active, even without an increase in fitness (13). Small amounts of physical activity already make a significant difference. The greatest health gains are achieved when you’re going from engaging in no physical activity at all to doing some activity (6). Of course, if you do more it will be better for your health and fitness, but this does not mean small amounts don’t count. This is why the WHO promotes that ‘Every Move Counts’ (14), and why the 10,000 Steps Program promotes that ‘Every Step Counts’.

Good luck being active every day!

A shorter version of this article was also published by The Conversation on 16-01-2024, and can be read here: The Conversation - Thinking of using an activity tracker to achieve your goals? Here's where it can help - and where it probably won't.

References:

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2. Vetrovsky, T., Wahlich, C., Borowiec, A., Jurik, R., Smigielski, W., Steffl, M., Tufano, J., Drygas, W., Stastny, P., Malek, L., & Harris, T. (2021). Benefits of physical activity interventions combining self-monitoring with other components versus self-monitoring alone: a systemic review and meta-analysis. The Lancet. https://www.sciencedirect.com/science/article/abs/pii/S0140673621026301
3. Australian Government Department of Health and Aged Care. (2021). Physical Activity and Exercise Guidelines For All Australians - For Adults 18 to 64 Years. https://www.health.gov.au/topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians/for-adults-18-to-64-years
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The Activate Your Everyday Series is proudly supported by the Queensland Government and Health and Wellbeing Queensland through ActiveKIT Round 2