On the Garmin 645 and also in the Garmin Connect app it's possible to setup the heartrate zones based on the Max. Heartrate (default) or the Lactate Treshold.
I don't know my exact max. heartrate, I'm just using one of the popular formulas. But I've got a Lactate Treshold in BPM which has been computed automatically by the Garmin 645.
What's the better option for the heartrate zones definition now - by Max. HR or Lactate Treshold?