I think the most important question to answer is - if you repeatedly did lab testing and periodically had good estimates of LT1, how would you use it to guide endurance training?
Summarizing the thread as follows, there are several camps or schools of thought:
- “keep stress low” camp that aligns with Seiler’s polarized recommendations to train endurance below the low aerobic threshold (where ‘mostly fat’ fuel switches to fat+carb fueling). Based on the ‘you are training endurance too hard, and not hard enough above threshold’ point-of-view
- “lab performance” camp that aligns with San Millan and focuses on the use of lactate and gas exchange testing to determine LT1 and do most endurance train right at LT1
- “power-based performance” camp that balances recovery with slowly pushing up endurance performance
- “RPE” camp that observes cardio and metabolic endurance training adaptations are driven by relatively low intensity and provided you don’t go too low, just do more of it by RPE (along with recoverability)
- “LT1 proxy” camp that will use any reasonable sounding proxy for LT1 to either train endurance at Seiler polarized or ISM LT1
That’s basically how I would characterize it. The DFA a1 stuff falls under the last bullet, and like many other low aerobic proxies it may or may not help you identify LT1 without lactate and gas exchange testing.