[jatx]

VO2 Max is the maximum amount of oxygen a person can utilize
relative to body weight. You measure it on a treadmill with a tube in your mouth and a clip on your nose. The relevant metric is kilograms per minute of oxygen uptake. No athlete, professional or otherwise, can monitor their effort relative to VO2 Max during a workout outside of the lab.

What is your method of measuring kilograms per minute of oxygen intake relative to VO2 Max during a workout?

When I was last at the US Olympic Training Center in '93, they readily admitted that they administer the test primarily to ascertain potential. It isn't really an actionable number, and most people don't have access to the test. Which is why I recommended getting your MHR tested prior to beginning serious interval work.

However, I never said that there is no reason to train at or near your lactate threshold, which I assume you're using interchangably with what I'm calling "anaerobic threshold." But you must do so very carefully and in the context of a well-planned program. You're just wasting your time and asking for injury, over-training or worse if you try to go out and do it without a HRM. Effective interval work like this requires operating in a narrow 5-8 bpm band, which most people cannot adhere to without direct feedback from a HRM. Go over the line into your anaerobic phase and you lose the training effect. The whole point is to push it right up to the red line and learn how to keep it there for a sustained period without blowing up.

IMHO, though, the real value of a HR monitor is its ability to focus you on the right level of effort during longer endurance workouts. Few people get this right on their own.