Web API call or approach to get wear time?

[jniml55k]

Is there a way to use the Web API to figure out how long the user has been wearing the Fitbit each day? The only thing I can think of is getting Intraday Heart Rate and crunching those numbers to look for gaps. Are there other, simpler ways to get this information?

[JohnFitbit · Accepted solution]

Hi @jniml55k,

The intraday heart rate endpoints would probably be the best way to determine if the user was wearing the device all day.

Though, even this method is not guaranteed since the endpoints can return values of 0 if the device was not getting a strong enough reading (band too loose/too tight). For questionable timestamps, you could also maybe cross-reference the data returned from the Activity Intraday Time Series endpoints to see if there were any activity for those timestamps.

I hope this helps. Let me know if you have any additional questions.

[Kevin_H]

Edit 10/15: l had made a bad assumption re: METs vs. wear. I removed my Charge 4 and laid it on my desk for half an hour, and the minutes from that period had METs = 1.0 (= BMR). It appears that Heart Rate will be a much better indicator of wear time as you described.

Hi John,

We've been addressing a similar issue hand I think there might be a better solution? Here are some numbers from our study using the Charge HR 3:

Total participant Fitbit minutes: 425,554

Total minutes without a heart rate: 119,733 (no matching minute from the HR intraday endpoint)

Total minutes with zero METs: 13,347 (METs coming from the calories intraday endpoint)

Since we're getting METs values for about 90% of the missing heart rate values we are assuming that Fitbit is calculating METs with pure accelerometer data when the pulse sensor is not contacting the skin, which can happen when resting your arm while sitting such that the device is raised off the skin, but more importantly when active possibly due to the pulse sensor moving across the skin. Our study staff assures us they train the participants to wear the Fitbit snugly, so I'm assuming it's being worn correctly. 

So would METs less than 1.0 be a better indication of non-wear?

(When I over-think this I remember that it's possible for a participant to carry the Fitbit in a pocket or purse, or to be driving or using public transportation and I come back to my understanding that the data is very good but imperfect. Still I would like your thoughts on the 10:1 relationship between minutes without heart rate and minutes without METs)

[abc123455555]

Hi John, it's 2023 now. Is Intraday heart rate still the best way to measure wearing time? Or is there a new way that we could use?