Average Smo2 and tHb in the Lap+Session messages an array

kcfwpi 6 days ago

Hi folks,

I'm attempting to extract Smo2 and tHb fields using FIT SDK version 21.141. There are summary (avg, mix, max) values of these fields available in the Lap and Session messages. They are named:

avg_total_hemoglobin_conc
min_total_hemoglobin_conc
max_total_hemoglobin_conc
avg_saturated_hemoglobin_percent
min_saturated_hemoglobin_percent
max_saturated_hemoglobin_percent

Per the FIT profile these are all arrays. I can't find a description of why these are arrays. Does anyone know why, or give any guidance on how to extract this data? I can't figure out why these would be arrays.

Thank you

0 kcfwpi 6 days ago

Update: I wonder if the total_hemoglobin and saturated_hemoglobin summary fields in the Lap and Session messages are arrays because it's possible for athletes to wear multiple sensors simultaneously. I.e. one on each thigh. So each sensor is a different element in the array. If that's the case, then why are the SmO2 and tHb fields in the Record message also arrays?

0 Ben FIT 4 days ago in reply to kcfwpi

The total_hemoglobin and saturated_hemoglobin summary fields are pretty old, and I was not able to dig up any history on them. More than likely the fields were added to the FIT Profile during development of the ANT+ MO2 Device Profile and before there was a clear intent for them. If the fields were meant to hold the data from multiple sensors, then the corresponding fields in the Record message should have been arrays too.

The best practice for Garmin devices is to use the manufacturer's CIQ data field(s) instead of the native integration. That is the only option for Edge bike computers since there is no native integration for MO2 sensors. For other device manufacturers that support MO2 sensors, the native values in the FIT file are typically the only option.

0 kcfwpi 4 days ago in reply to Ben FIT

Oof, this is really messy. I have 7 sample FIT files that contain SmO2 data, and there are 5 different ways that they're being stored. With the mix of sensor manufacturers and and watch/bike computer manufacturers this could benefit from better definition in the FIT Profile so that it's standardized across all of those manufacturers.