A training tracker can record sensor data directly to .csv. To find the .csv generated by a training tracker is a bit tricky. First, you have to tick on in a training tracker, that you want .csv. Only then a folder is generated.
I could find the folder with the .csv by connecting my Galaxy S5 to the PC, and then seraching for .csv files on the phone.
This PC\Galaxy S5\Phone\Android\data\com.atrainingtracker\files\CSV
Once you got the .csv files, they are very clear. A clear time stamp, a clear data structure. Similar to the data struture generated by Data Scientist Max Candocias .fit to .csv Python script.