New 235 user here. I'm new to interval training, been doing medium/light strength training and rowing about 3 months. Just started doing all out intervals on the rower. The watch will often show max heart rates well over the value reported to Garmin Connect. I'm assuming that's simply due to averaging over a time period, but my question is: "How long do I have to sustain a given heart rate for that be reported for the day's max heart rate?"
Being new on my fitness journey, my max effort intervals are pretty short (currently doing 30s work / 1:30 rest), and I can hit 176 bpm as displayed on the watch, but then when I look at my logs it will show it as something like 138bpm. Does anyone know the averaging window size they're using or how this is calculated?