I have had the Sense for about 1 month. Early on, I noted that the heart rate achieved thru exercise using the same workout tape appeared lower than I achieved with the Ionic and appeared too low given my physiologic response of increased breathing, easy fatiguability etc. I then began using both the Sense and Ionic when exercising. I have used both next to each other on the same non dominant extremity and on different extremities adjusting the appropriate device to the appropriate non or dominant extremity. The results are always the same. For about the first 10 minutes the Sense under estimates my heart rate as recorded on the Ionic by 25 to 40 beats per minute. At times, the Ionic has had my HR at about 150 which is close to my maximum while the Sense shows 105-110 range. After 10 minutes, the Sense and Ionic essentially give the same HR as the HR measured by the Sense rises to the Ionic level.
I chatted with a representative from Fit bit who stated: (1) the two devices measure HR differently and (2) there is no way to calibrate or recalibrate the Sense.
If the Sense is really underestimating HR by 20-40 beats per minute during initial exercise, it stands to reason that there is a risk that an individual could exercise in a dangerous HR level without knowing it.
This issue needs to be resolved.
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