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  • Writer's pictureStephanie Collins

How Accurate Is My Fitness Tracker?

I, like almost everyone these days, wear a fitness tracker. I personally use an Apple watch but there are many out there to choose from. Most of them function pretty similarly. When I first began my fitness journey I was on a popular weight loss program. They used an app to track calorie intake and that app, like many, synched to my fitness tracker. This particular program would give you additional calories based on the amount of calories you burned working out or walking throughout the day. I did just that for sometime. At that point I was at a starting weight that even with eating back the calories I was getting results because I was in a deficit. I continued to get results this way for 3 years and during that time I lost my first 60 lbs. What I didn’t realize at that time was that consuming the additional calories was likely slowing my results.

In 2018 I reached the huge milestone of losing 60lbs and weighing 200 lbs. I had begun walking my dogs and doing popular 30 minute HIIT videos in my living room. I also worked in a busy hospital laboratory and racked up the daily steps. I continued to follow my plan and I continued to eat back the calories burned. I started going to the gym and shortly after that started working with Ryan as my trainer. Right around this time my results stopped. Nothing had really changed. If anything my cardio had increased and I was starting to strength train. Ryan was always super passionate about health and fitness and helping his clients so he put a lot of time into helping me figure out that not only did I need to stop eating back my calories burned during exercise but it was probably time to get off that program as by design it’s only meant to get you so far (Yet another example of how the vast majority of the fitness industry is set up to make you reliant on them so they continue to profit).

Now I’m really not knocking this particular program because it did get me very far and gave me a very basic understanding of calories/macros/energy balance. Ryan had me download MyFitnessPal and start tracking that way. The thing is that this app also suggests you eat back calories burned. So I did. However I was now at the point where eating back calories burned was putting me out of a deficit and I was maintaining. Ryan again told me to stop eating back calories burned and this time I listened. Guess what? My results started rolling in again. Now I’ll tell you that at this point I didn’t really understand why eating back calories burned was what had slowed and eventually stopped my results but I did at least understand that was the issue.

Around this same time I was working out with a small group. It was always very frustrating to me that one individual who put in the minimum amount of effort always had the biggest calorie burn according to her fitness tracker. It all seemed so wrong that I was actually working hard and exerting myself and this person was burning twice as much as I was. Something Ryan had said started to run through my mind “most people underestimate the amount they consume and overestimate the amount they burn”. How could we possibly be overestimating what we burn when we all wear these fitness trackers? So let’s dive into that question a little bit.

A recent study done by The Stanford School of Medicine shows that activity trackers are actually really accurate in the tracking of most metrics….except energy expenditure. It is probably off by a very significant amount when it comes to energy expenditure. This study measured 7 devices on 60 diverse participants and showed the heart rate measure to be accurate within 5%. This same study found that NONE of the devices measured energy expenditure correctly. The most accurate was off by 27% and the least accurate was off by 93%. People make life decisions based on the data from these devices so please keep in mind that they are not held to the same standard as medical devices.Manufacturers do test the accuracy extensively but there’s no way for us as consumers to know how accurate that information is or the process used to test these devices. The takeaway of this study is that the heart rate data is fairly accurate but if you’re trying to decide how many slices of pizza you can have based on your energy expenditure the number on your tracker is way off the mark and so that's a really bad idea. The team at Stanford Medical School is actively working on a second phase to follow up this study that will be done in everyday use and open exercise and not just conducted in a laboratory environment.

Some things to keep in mind going forward. Many factors determine how certain fitness trackers work.

  • The algorithm used

These algorithms typically base your caloric burn off of your data inputs when you sign up

For example: your height, weight, predicted activity level, gender, age will all determine how many “calories'' you burn. It's not a bad thing to see how many calories you burn but it will greatly reduce your weight loss later if you think you're burning 900 calories when in actuality you're only burning 450.

  • The type of activity your doing

Many fitness trackers will have options for you to pick from such as spinning, walking, strength training. While yes all of these burn calories typically the cardio options are heavily inflated. Instead of burning 700 calories in a 60 minute cardio session most might only burn 250-400 depending on weight and overall exertion.

  • Certain trackers will add the calories back into your diet

When your goal is to lose weight you need one thing: a caloric deficit. If you burn 500 calories from your workout you should not eat them back. You most likely are creating your deficit from exercise and a caloric decrease generated in your intake. Eating back your calories from half of your generated deficit will defeat the purpose and greatly slow down your weight loss.

  • Counting step inflation

When it comes down to counting steps some fitness trackers don't accurately count steps or heavily inflate the steps. Depending on where you wear your tracker things such as movement of the arms or shoulders can add steps so you perceive you have more steps then usual. This further delays weight loss because 10,000 steps per day is much more significant then 6,000 steps per day for weight loss.

  • Overestimation of calories

Most fitness trackers will overestimate your calories. So much so that sometimes at the start of following those calories the person ends up gaining weight. In order to see how accurate the caloric intake of these trackers are then you should try the calories allotted to you for a whole week. During this week weigh yourself each morning and check the weekly average to see where your weight is by the end of the week.

Fitness Trackers are another tool that you can use but don't give results in a snap of a finger. They are a tool to help control variables. The most important variables for weight loss should always be accounted for and tracked such as caloric intake and overall energy expenditure. Use your fitness tracker as a variable that is consistent with you and use it as a baseline.

Sometimes we need a little help learning how to navigate and control our variables to be successful in our fitness goals. I know I absolutely needed the guidance of a coach. I still need his guidance even though I’m now a coach myself and successfully help people reach goals every day. If you're looking for coaches who can help guide you along the path for better and easier results feel free to reach out to myself or Ryan and we will work with you on your health and fitness journey.


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