I don’t use a fitness tracker.
I have no idea how many calories I burned yesterday, how many steps I did, or how many miles I walked.
Nor, quite frankly, do I care.
What got me thinking about the subject of fitness trackers was a book I was reading the other day, about a guy who used to be in the Special Boat Service, or SBS, which is the special forces unit of the Royal Navy.
He was in Afghanistan, on a mission to sneak up on a Taliban compound and take out a key target.
Normally, his team would have approached the building at night, moving in and out of the area very quickly.
But, they’d received intelligence that the area surrounding the building was mined.
This meant they had to sweep the area for mines, which slowed the operation down considerably, and led to a two-day s**t storm with enemy soldiers.
Even worse, it turned out that the intel was bad. There were no mines.
So, what does all of this have to do with fitness trackers?
Members of the special forces aren’t the only ones who need to be wary of bad intelligence (or intel as they like to call it in the SBS). It’s also a problem for anyone who wants to get in shape.
How Accurate Are Fitness Trackers?
A lot of the intel that people are obsessing over, be it from body fat tests, sleep apps, fitness trackers, food intolerance tests or whatever else, has the potential to throw you off course, either because it’s inaccurate, or because it’s interpreted in the wrong way.
Much of it, at best, is background noise.
At worst, it can slow your progress or even send you off in completely the wrong direction.
In a study of fitness trackers, none of the devices tested (the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2) measured calorie burn accurately.
Even the most accurate device was off by an average of 27%. The least accurate was off by 93%.
Some apps used for measuring heart rate can also get it wrong.
A study in the European Journal of Preventive Cardiology found a huge degree of variability in the accuracy of commercially available heart rate apps, even those using the same technology .
In some apps, there were differences of more than 20 beats per minute compared to the gold-standard ECG – which measures the electrical activity of the heart using leads on the chest – in over 20% of the measurements.
Heart Rate Variability
Heart rate variability – a measure of the variation in time between each beat of your heart – is something else that can be tracked with an app on your phone or watch.
The idea is that you can use heart rate variability to tell you when you’re ready to train again, when you need to rest, or when you need to take it easy.
But does it actually work?
At this point, the jury is still out.
On the one hand, you have research to show that an endurance training program guided by heart rate variability can improve your fitness , as well as provide information on how well you’re coping with a training program .
However, different apps give different recommendations. That is, some tell you to train while others tell you to rest.
And not everyone is convinced that heart rate variability can be relied on to guide your training decisions.
Here’s an interesting story from Scott Johnston, an endurance mountain sport coach at Uphill Athlete, where he explains why he stopped using heart rate variability apps:
“One interesting anecdote that sheds some light on our skepticism came from private communications with the coach of a World Cup cross country skier. This coach was tracking the skier’s heart rate variability using some very high-end software.
“The data was collected at night while the skier slept and only the coach could view the data. This prevented the athlete’s anxiety from affecting the test results or performance. Overnight tests should provide the most reliability about recovery status.
“During one arduous race week, the software warned that this skier was way into the red zone of fatigue and should rest. That same day she won a World Cup race.”
“[Heart rate variability] is great to describe how the training has gone—to look back and, with hindsight, see exactly when things were clicking and where you went off the rails,” writes Alex Hutchinson, author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.
“But the evidence that you can really use it to alter your training in real time and measurably enhance performance is still thin at best.”
Heart Rate Variability and Muscle Growth
If you’re trying to gain muscle and get stronger, heart rate variability doesn’t appear to be much help either.
In a study carried in the European Journal of Sport Science, researchers compared a group who trained with a fixed 48-hour period between strength training workouts with a group that trained only when heart rate variability had returned to normal.
There was no significant difference in muscle growth or strength gains between groups. In fact, strength gains were greater in the group who took a fixed 48-hour rest between workouts, although the difference didn’t reach statistical significance.
“I’ve experimented with heart rate variability in many clients myself when it became popular,” explains business consultant turned physique coach Menno Henselmans.
“My experience is that it doesn’t help at all and can easily backfire. When you wake up and your heart rate variability says you haven’t recovered, this can drain your motivation to give maximum effort and therefore become a self-fulfilling prophecy. Heart rate variability says your workout is going to suck, you believe it, and therefore the workout indeed sucks.”
Rather than place your trust in any single measurement or observation, I think it’s far more useful to build your own personalized dashboard of data points, some of them subjective and qualitative (such as how you feel), and some of them quantifiable and objective (such as how well you perform).
Food Intolerance Testing
It’s not just apps that have the potential to deliver bad intel.
One of my friends recently splashed some cash on a food intolerance test, and was telling me about a bunch of foods that he was no longer “allowed” to eat.
However, the effectiveness of these tests remains to be established, and he may well be depriving himself for no good reason.
A position statement on the subject of food intolerance tests from The Canadian Society of Allergy and Clinical Immunology concludes that there is no research to support the use of these tests to diagnose or predict adverse reactions to food.
To quote the authors directly:
“There is no body of research that supports the use of this test to diagnose adverse reactions to food or to predict future adverse reactions. The literature currently suggests that the presence of specific IgG to food is a marker of exposure and tolerance to food, as seen in those participating in oral immunotherapy studies. Hence, positive test results for food-specific IgG are to be expected in normal, healthy adults and children. Furthermore, the inappropriate use of this test only increases the likelihood of false diagnoses being made, resulting in unnecessary dietary restrictions and decreased quality of life.”
Allergist Stuart Carr, a co-author of the position statement, often has people who have had food sensitivity (IgG) tests referred to him.
At which point, he has to break the news that they’ve paid big bucks for something that offers no useful information.
“When I see a patient come into my clinic, and they say we had this [IgG] test done, they will reach in their bag and try to hand me this booklet of results,” explans Carr. “I’ll say, I don’t need to see that, and explain why we can ignore it.”
Thanks to smartphones and watches, it’s possible to track more data than ever.
However, the fact that something can be tracked and recorded doesn’t necessarily mean that it’s worth tracking and recording.
Nor is it a guarantee that you can use the information to make better decisions about how to train and what to eat.
SEE ALSO: THE FLAT BELLY CHEAT SHEET
If you want less flab and more muscle when you look down at your abs (or where they should be), check out The Flat Belly Cheat Sheet.
It's a “cut the waffle and just tell me what to do” PDF that tells you exactly how to get rid of belly fat. To get a copy of the cheat sheet sent to you, please click or tap here to enter your email address.
ABOUT THE AUTHORChristian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.