Changes

The best way to measure FatMax is using an incremental stress test while measuring oxygen consumption and carbon dioxide production to get respiratory exchange ratio. That's part of a standard [[VO2max|V̇O2max]] test, but not something that's easily or cheaply available to most runners. Another alternative is to look at [[Lactate]] levels. There is some correlation between the initial rise in Lactate and FatMax<ref name="a585"/>, and while not perfect, I think it's good enough. Lactate meters are becoming cheaper and more widely available, with the promise of continual lactate monitoring coming soon. The initial rise is Lactate is different from what is normally meant by [[Lactate Threshold]], which is the transition from moderate to hard exercise (aerobic to anaerobic). This initial rise is sometimes call called the "First Lactate Turn Point" or "Aerobic Threshold". Definitions vary, with some studies using any rise from resting lactate levels, some using 0.5 or 1.0 rise from resting levels, or a fixed 2.0 level of lactate.

My practical advice is that FaxMax training is worthwhile, but don't get hung up on the exact intensity. Instead of looking at heart rate zones, simply ensure you go slow enough that you can keep it up longer without feeling exhausted. The pace should be slow enough you can hold a conversation, which seems to be one of the best intensity metrics, even now , with so much available technology. How long will depend on your fitness, but longer is better. Decades ago, coaches recommended "2-3 weekly interval sessions, a weekly long run, and as much low intensity as you can handle<ref name="Bowerman"/>", which still seems to be true.