Sense - BPM seems very inaccurate while working out.

[DanRichard]

Hi everyone, this is my first post ever on the community forums! I just got my new sense Fitbit and this is my first ever smartwatch and looking forward to using it with gym training, which I've been doing for about 30 years now. Today was my first workout with the watch on and everything went great when I did the weight training it seem to be tracking properly with the heart rate being accurate and all that stuff. I wear wristbands when I train however I am able to move the watch up a little bit up my wrist to make room for the bands and it still seems to track fine and no issues.

I did 75 minutes of weight lifting and then went to go and do some light cardio in the form of spinning. Took off the wristbands put the watch lower down and tightened it up, had myself a drink and then went to go to start my spinning. I have a sore knee so the spinning was very light with no resistance and a sustained speed of around 95 RPM which is really easy. I was shocked to see my watch registering a BPM of $130 with this very very light cardio. I then use the built-in BPM grips on the bike to check and it registered a 90, which makes more sense. I stopped and then used another bike and once again checked my pulse and registered a 90, and my Fitbit was still measuring 130. While I was weight training and hitting particularly intense sets it would hit about 120 or 125 which makes sense, so I have no idea why the spinning was hitting 130 and was nowhere near as intense. Any clues why my watch was blasting up the BPM that much?

Moderator Edit: Clarified subject

[SilviaFitbit]

@DanRichard Welcome to the Fitbit Community. Thanks for the detailed information shared. 

Glad to hear that you've been into fitness for a while now. As with all heart-rate tracking technology, accuracy is affected by personal physiology, device location on your arm, and type of movement.

For a more accurate heart-rate reading:

• Wear your Fitbit device on top of your wrist, and make sure the back of the device is in contact with your skin.
• When you’re not exercising, wear your device a finger’s width above your wrist bone.
• During exercise, wear your device a bit tighter and higher for an improved fit. The band should be snug but not constricting (a tight band restricts blood flow, potentially affecting the heart-rate signal). Many exercises such as bike riding or weight lifting cause you to bend your wrist frequently, which could interfere with the heart-rate signal if the watch is lower on your wrist.

Also, feel free to check out this article for factors that can affect your heart-rate reading on your Fitbit device. 

Hope this helps. 

[SunsetRunner]

Hi @DanRichard ,

First of all, follow @SilviaFitbit  good advices.

Besides that, your feedback seems to confirm my current opinion that Sense heart rate (HR) accuracy depends very much on the kind of activity. I haven't yet explored enough how choosing a different type of activity on Sense Exercise app can affect Sense HR accuracy. In principle, you should choose the app exercise that fits the exercise you are about to do.

Why this rambling? Because putting together my experience and other users experiences, I conclude that we can find a wide range of Sense HR accuracies (or inaccuracies). @SilviaFitbit  advices are the first step to get the best accuracy possible, but I would say that even so, you may not get always an acceptable accuracy.

One example, from my own experience. I do walkings using the Walk option in the Exercise app. When I walk outdoors along a flat path, most of the times I get good HR values. Often it happens having an initial spike with too high HR values, but after a few minutes, HR values come down to the right values.

When, for some reason, I can't do my daily outdoors walk, I do it indoors, often walking back and forth in corridors or from room to room. In this case, it happens often that Sense HR starts to go up and up until totally unrealistic values, sometimes almost twice the real HR, confirmed with a medical pulse oximeter. And in both cases I am wearing my Sense the way Fitbit recommends and @SilviaFitbit  described above.

Why these differences with Sense HR accuracy in both cases? Different types of arm movements while walking? Fitbit HR algorithm better adapted to one case than the other?

I still couldn't find a general solution for the situations where Sense HR is not accurate enough, sometimes wildly inaccurate. The only advice I can give is what I do: keep trying different ways. Maybe you'll find one that works for you. Or maybe, meanwhile, Fitbit finally manages to fix these HR inaccuracies.

[DanRichard]

Hi Silvia, thank you for the welcome 🙂  I don't want to come off as unappreciative of your feedback, however I feel like that's a fairly generic answer that would be sent to anyone mentioning a bpm inaccuracy.  In my case, there is definitely something strange going on, and I would like to clarify a couple of things:

• I've worn an HRM chest strap many times, so I am relatively familiar with what my bpm should approximately be depending on the fitness activity.  That's why I know the 130 is impossible for an easy spinning session.
• The wrist positioning from my testing with my wife's Sense is fairly forgiving.  When worn higher up my wrist due to wearing wriststraps, the readings are just as accurate as wearing it further towards my hand.  I keep an eye on my bpm level throughout my weight training, and I can honestly say it's accurate during the entire session and "angles" don't seem to affect it.
• This is a big one:  If I walk in the gym and go straight to the stationary bike and DON'T activate a fitness mode, the bmp reading is totally accurate and matches what the heart rate monitor on the bike says.
• If we run the same scenario as described in my original post and keep my hands down at my sides instead of up on the handlebars, I still get a super high reading, so it has nothing to do with angles.
• I am under the impression that any issues interfering with heart rate signal such as angles, poor wearing of the watch etc would case your readings to be too low, not too high.

So with that said, I believe that there are two possibilities that I am going to try out next:

1. Could wearing the compression wristbands be affecting the way the watch reads my heart rate signal when I take the bands off and put the watch over the same area?
2. Does switching immediately from the weight lifting program to the spinning program somehow generate an inaccurate bpm?  I will test this by not changing the program and keeping it on weight lifting mode when I use the bike and see what happens.

I'll post an update once I've tried all this out 🙂

[DanRichard]

Thanks Miguel, I agree there's definitely something weird going on and @SilviaFitbit 's advice seems a little too basic and I don't think it's related.  I'm going to keep trying different things to see if I can pick off what's going on.  It's funny to see the stats at the end when I burn 500+ calories in a 65 minute weight lifting session but then burn 200+ calories doing 15 minutes of easy spinning.  Just doesn't add up at all.

[SunsetRunner]

I agree, Dan. The calories you mention don't add up. But as calories are calculated by Sense based on its heart rates... the issue is probably on the heart rates.

Good luck and hope you find a solution. Though by reading this forum posts, maybe it will not be easy, if possible at all. The only good solutions I found so far are wearing either a chest strap or an arm band, but I don't know how they will work with weight lifting. Besides, those would imply leaving Sense out.

[DanRichard]

Well the important part for me is that it's accurate when weight lifting, which it is.  My light cardio sessions after are more for nutrient delivery and increased blood flow post weight training when I take my post workout shake so it's not the end of the world if it doesn't track properly.  I'll keep messing with it and see if I can find a winning combo.  Take care!

[SilviaFitbit]

@SunsetRunner and @DanRichard Thank you so much for taking the time to share detailed information about what you're experiencing. 

I see where you're coming from. We’re aware of it and are working to identify a resolution as quickly as possible. We're sorry for any trouble. We appreciate your patience and look forward to getting you back on track.

Your understanding is appreciated. See you around.