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What To Make of Your Fitness Tracker Numbers

Oct 31, 2016

What To Make of Your Wearable Fitness Tracker Numbers:

Fitness trackers seemingly exploded to the forefront the US consumer market in 2009 when Fitbit released its first model. Since then, big names like Apple, Samsung, and Garmin to name a few, have released their own wearable devices, and countless companies have released fitness tracking apps for smartphones. The wave of momentum for trackers seems to still be growing as a recent report found a full third of Americans use a fitness tracking devices (note: these numbers do not count smartphone apps).

This comes in spite of recent legal challenges questioning these devices as well as a growing amount of recent scientific evidence purporting that branding and reliability of fitness tracker data most of the time is not 100% accurate. But does this then mean that these devices are completely and utterly useless? The short answer is not necessarily, if you keep certain considerations in mind.

Fitness trackers nowadays can come with an impressive offering of nifty technologies from sleep tacking, to VO2 max (new on the Garmin Vivosmart HR), but the big three features from an exercise standpoint tend to still be heart rate, calories burned, and step count. These three are consequently the three features that are questioned the most extensively in scientific literature. The most recent of which coming in the form of a research letter published in JAMA’s (Journal of the American Medical Association) cardiology journal. The brief publication echoes a very simple message that some have been hearing quite a bit lately: the heart rate monitors on some of these devices are not 100% accurate, and some more so than others (see photo below). Another recent study suggests calorie tracking features may be even further off the mark. As for step count, the pedometer technologies in fitness trackers do rather well in this area of performance when dealing with basic activities like walking or stair climbing, but may start to err a little when it comes to more complex activities (i.e. tracking steps during a zumba class).

Take a look at the results of the JAMA research letter (see figure to the left). What the researchers did was simply compare how the heart rate measure for various fitness trackers matched up with actual electrocardiogram (EKG) data. As you can see, some devices perform better than others. Polar and Apple watches top the list, but the shocker to some might be where the Fitbit Charge HR ranks. These devices, according to the study, have a high range of variability and thus have a greater chance of being off by a few beats, as much as 8% according to the researchers’ numbers. Now part of the reason for why could be traced to the get what you pay for factor. Fitbit Charge HR hovers in the $100-$120 range, while Apple watches consistently go for $240 or more.

The Polar H7 is an outlier on this list as it offers what is currently the best feasible solution for accuracy problems we currently have with fitness trackers. The H7 actually isn’t a watch at all; it’s a chest strap monitor. You attach it just below the sternum and sensors on the underside of the strap actually measure the flow of electrical current that the heart produces. Wrist worn trackers have no such electrical sensors; they utilize a technology called optical sensing. Basically, optical sensing uses LED lights and a sensor to see the changes in blood flow in the capillaries (the smallest blood vessels) in your wrist and extrapolate a heart rate that way. The problem is, things like excessive movement and sweat, and even simply your heart rate being too high, can dupe these kinds of sensors. There are plenty of things that can go wrong but there are two very basic and broad tips on handling your own flawed, yet still useful, fitness tracker data and a solution for if the inaccuracy still bugs you:

1: If something looks way off, it probably is

If your tracker is saying your heart rate is 160 after a mile walk, or 70 after a hard mile run, don’t panic because it, in all likelihood, is wrong. Self-checking pulse periodically is and easy way to remedy this. Simply find your pulse on the right side of your neck, or on the thumb-side of the bottom of either wrist (the wrist tends to be more accurate but harder to find a pulse) with your middle and index finger. Count your pulse rate for fifteen or twenty seconds and multiply by three or four depending on how long you count for (15x4/20x3=60) and you have your heart rate.

Calorie counts being off is trickier to figure out, but once you have some general averages in mind, you will start to learn to recognize when your tracker may be off the mark. The average person running a mile at a decent pace burns roughly 100-150 calories depending on their fitness level, whereas walking burns anywhere from 80-120 calories per mile. Cycling gets trickier because the number of calories burned during a mile cycling is more dependent on speed than running or walking are. Assuming a speed of 10-15 mph, which is a fairly reasonable leisurely pace for most, one may burn anywhere from 40-60 calories per mile. Going faster, or significantly uphill may bump those numbers a bit higher. While engaging in any of these activities, knowing how far you’ve gone and what your average speed was, can give you a number to verify whether your fitness tracker is in or out of the ball park for these activities.

And just to provide another ballpark number, resistance training sessions, like we do in sessions with our clients, can carry a caloric expenditure value anywhere from 300-500 depending on what the trainer has selected for the session.

2: Notice the trends

I would say the biggest reason for hanging on to your fitness tracker is that it provides you with accessible data, even if that data may be a little skewed because over time, that data can shed some light on valuable trends in one’s fitness progression. If for example, you’re noticing that after a couple weeks of training/exercising your exercising heart rate has been going down doing similar activities, does it really matter if the actual numbers are six beats off reality? What should matter is regardless of the data, you’re seeing a positive change in the mid to long term; and that’s where fitness trackers are their most useful. Bottom line: don’t let the actual numbers dictate how you feel about your fitness tracker because while they are lacking in the specific details, they still have valuable big picture information to offer their users.

3: Give the chest strap monitors a try

The idea of exercising with something around one’s chest sounds like an uncomfortable experience. The concerns with such straps usually include chaffing from the band, the band slipping once one starts working up a good sweat, and restriction of breathing. All are valid concerns. Also, these devices typically measure heart rate only, so they don’t have for example the sleep tracking or calorie counting technologies like some Fitbit models have. But some other facts about these straps might be able to change your mind.

First of all: the price tags. Take the Polar H7 for instance. One can purchase such a device for somewhere around $50. Other makes and models can be found for even cheaper than that as well. Some straps actually feed their data back to a watch. If a watch is needed, it’ll set you back about another $40, but it still could end up costing less than an upper model Fitbit like the Charge HR, and definitely less than an Apple watch. Some other straps however are Bluetooth enabled and have apps to go along with them. Better still, many are compatible with a wide variety of other big-name fitness apps like Endomondo, Strava, Runkeeper, and MapMyRun.

Secondly, as previously stated, the technology provided by these straps is the most accurate cost effective technology. Some studies actually measure other wrist-worn devices against chest strap monitors due to their reliable reputation. If heart rate accuracy is a super important priority to you, trying a chest strap may be the gadget for you. Just don’t be too quick to throw out the receipt because comfort could very well be the deal breaker.


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