That's a good suggestion for a follow-up post. Thanks, James, for bringing it up. I avoided appearing as if making an advertisement for any single brand in the post. I personally don't use any of the trackers, but my friend and business partner does. He is a triathlete with an enviable track record in ironman competitions. He uses a Garmin tracker, and finds it to be in rather good agreement with his periodic gas exchange tests in the lab.