Add exercise with sets to a session

In my garmin connect iq app I do create a user session like following:

mSession = ActivityRecording.createSession({
    :sport=>ActivityRecording.SPORT_TRAINING, 
    :subSport=>ActivityRecording.SUB_SPORT_STRENGTH_TRAINING, 
    :name=>"Workout"
});
mSession.start();

// TODO: add a set with some data + add total workout statistic
// e.g. one set of benchpresses with 10 reps of 100kg within 40seconds

mSession.stop();
mSession.save();

I can't find any way to fill the default data of this session I only find things like createField which creates user fields.

So my question is how do I fill out the default fields of a strength training session? Namely following:

• time under tension
• pause time

And additionally how do I add default list entries? Namely:

• an exercise with sets and a weight and reps?

Currently, when I save my session I don't have any data but avarage heart rate, calories and time inside my workout.

What I tried so far - sadly it did not work, garmin connect app still shows empty total stats:

I tried something like following to fill out the workout statistics:

I found the number for the nativeNum field here (https://github.com/dgaff/fitsdk) because I did not find any Profile.xls(x) inside the current fitsdk download and this file seems to be the source for the numbers.

fTotalTime = createFieldWithUnit("Total Time", 1,  FitContributor.DATA_TYPE_UINT32, 7, "s");
fNettoTime = createFieldWithUnit("Netto Time", 2, FitContributor.DATA_TYPE_UINT32, 8, "s");
fNumLaps = createField("Laps", 3, FitContributor.DATA_TYPE_UINT16, 26);

fTotalTime.setData(100);
fNettoTime.setData(25);
fNumLaps.setData(3);

Function code:

hidden function createField(label, id, type, nativeNum) {
    return mSession.createField(
               label,
               id,
               type,
            {
                :mesgType => FitContributor.MESG_TYPE_RECORD,            
                :nativeNum=> nativeNum
            }
        );
}

hidden function createFieldWithUnit(label, id, type, nativeNum, unit) {
	return mSession.createField(
	   		label,
	   		id, 
	   		type,
    		{
    			:mesgType => FitContributor.MESG_TYPE_RECORD,			
				:nativeNum=> nativeNum,
				:units => unit
    		}
		);
}