Heart Rate without a Chest Strap…Don’t Rely on It!

In class we see this more and more…clients glancing down at their wearable technology. Do you own a heart rate monitor that does not have a chest strap? If so, it probably isn’t accurate. In fact during exercise, it can have an error rate upwards of 60%!

Wrist-only heart rate monitors use light to measure your pulse. The device shines a light into the blood vessels in your wrist, and then detect the changes in blood volume that occur each time your heart beats and pushes blood through your body. Sensors on the device detect how much light your blood vessels reflect back: Less reflected light means a higher blood volume.

Sounds great right?

Unfortunately it just is not typically accurate – particularly many of these devices appeared useless during intense exercise. There are some wrist-based heart rate monitors that seem to perform better than others but for our own unofficial ‘testing’ we put the Fitbit Charge through numerous recorded workouts.

Chest strap heart rate monitoring is proven to be much more accurate and comparable to an EKG. During our own “testing” during the same PSF Signature session, the ANT+ chest strap much more accurately depicted heart rate than the Fitbit Charge, which uses optical sensors on the wrist. The Fitbit was consistently way lower than the chest strap and therefore gave us a much lower calorie expenditure report as well.
In fact, Fitbit has been hit with another class action lawsuit (remember the skin irritation issue?) regarding the severe inaccuracies of tracking heart rate, specifically during exercise.

Check out what we found….

The Fitbit Charge recorded an average heart rate of 118 bpm during the PSF Signature class and a calorie burn of 335. It also indicated that the majority of time was spent in the “yellow” zone which although suggests ‘fat burn,’ the overall caloric expenditure is much lower in this zone as well as the ability to achieve an after-burn.


The chest strap recorded very different results. Almost double the calorie expenditure and an average recorded heart rate during the same workout over 30% higher. You can also see that over 80% of the workout was spent in the orange and red zones which is double from what we saw with the Fitbit.



You may think we like the chest strap because it is higher, however we like it because it is accurate. Anyone who has ever taken a PSF Signature session knows firsthand that your heart rate definitely skyrockets – this particular class was no exception and a quick manual pulse check definitely supports the chest strap!

So is your Fitbit or similar device worthless? Probably not. I wear one (mostly because it is PSF red 🙂 but also I think it’s interesting to see my steps and compare my day-to-day performance. However I take into account the heart rate and calorie readout is grossly inaccurate, I do think it’s good to see how different days stack up against one another.

It’s worrisome that people rely on optical wrist sensor technology to dictate their workout intensity – it isn’t accurate and can deter your results!

Bottom line…if you are interested in tracking your fitness performance…you simply must be monitoring your heart rate by wearing a chest strap! You don’t need a special watch – we love the MotiFit app (which you can also use on an Apple Watch if you have one).


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