Glucose Tolerance Test and CGM
OK, I’m persuaded to wear a CGM. I understand the parameters that you’d like us to be able to operate within. Is there some reason we shouldn’t self administer a glucose tolerance test using the CGM.? I understand I can’t test for insulin but is value otherwise?
Does sunscreen prevent you from making Vitamin D?
Should you intentionally wait to apply sunscreen in order to be in the sun for “enough” time to make “enough” vitamin D? I listened to the sunscreen podcast but did not notice any discussion about this. An add-on question is, if sunscreen does prevent you from making vitamin D, then can you please provide guidance on an optimal range of time to spend in the sun before applying sunscreen? Thank you
Lactate independence of heart rate on "off days"
I use heart rate as a heuristic for lactate level. But sometimes I have days where my heart rate seems suppressed even though I'm working just as hard and at the same level (treadmill). I entirely identified with Iñigo's comments about the occasional off day of zone 2 training, where he couldn't get within 15 beats of his usual target heart rate. To me it begs the question: Even if there is some explanation for the suppressed heart rate that day (bad sleep, low energy reserves, distracted mind, etc.), do the muscle mitochondria know the difference? Aren't they still "working" to churn out ATP just the same assuming the mechanical metrics of the workout are the same? That is, is the actual lactate level still the same (i.e., near the threshold) for the identical workout even when the heart rate is lagging for some reason OR is lactate production indelibly tied to heart rate because it's a reflection of the lower amount of oxygen being used?
What is the rate-limiting step of oxygen delivery to muscle (and thus the rate-limiting step for VO2)?
You have obviously covered VO2 Max a lot, but I'm still a bit confused about where the rate-limiting step lies. Am I limited by my mitochondria, my vasculature, my cardiac output, or something else? If I target training at one of these but they're not the rate-limiting step, then my VO2 Max won't change. On a couple podcasts you've seemed to insinuate that it's mainly at the level of stroke volume (and thus zone 2 works predominantly by increasing LV End Diastolic Volume) but at other times it has sounded like the mechanism is by increasing mitochondrial flux through ox/phos, or through angiogenesis in skeletal muscle, or maybe even in O2 carrying capacity or lung mechanics. So in the complex system that gets O2 from ambient air into muscles for ATP generation, where does the rate limiting step lie? And of course, how do we target training that step to increase the VO2 Max?
What are the downsides of prolonged use of Ashwagandha?
I currently supplement with 425MG - 675MG of Ashwagandha per day and have found there to be tremendous benefit from doing so, however, I have recently learned that Dr. Huberman and others warn against prolonged use of Ashwagandha and I never really understood why. Based on the AMA you did on supplements, I know you also supplement with ashwagandha. Is ashwagandha something you take year-round, or do you cycle it? Are you afraid of the consequences of prolonged use or is it just anecdotal noise?