I would like to understand biochemical processes how lean muscle is conserved during high intensity interval training(HIIT). Intuitive understanding is : HIIT tells body that lean muscle is required and body should utilize fat instead through lipolysis. Is this intuition correct? If so, what are actual physiological mechanisms of signalling and implementing lean mass conservation during HIIT?
HIIT training is short burst exercise that if done correctly is hormetic. In other words it stimulates stretching in fast twitch muscle spindles to send afferent inputs to the hypothalamus to release more GH to re enforce the fast twitch fibers for the explosive burst. The side effect of the is the organism benefits from higher GH release and GH has two major effects......it signals more fast twitch growth by upregulating AMPK and IGF 1 pathways and more importantly......if you are leptin sensitive it directly uses fat for fuel burning over glucose and glycogen over 12-40 hrs later via upregulation of UCP1 and UCP3 in the newly formed muscle. Here is the key though. Most lifters or body builders tell to you to eat post work out.......wrong answer if they understood how the body works. Your better to fast after the HIIT because even a bite of a cracker or a sip of a energy drink immediately turn off fat burning peripherally. And this fat burning lasts up 96 hrs in some folks. Art DeVany mentions this in passing in his book but he is spot on the money. People who want performance need to eat post work out. People who are wanting to shred weight and build health and longevity need to use their leptin sensitivity to their advantage. Moreover.......why is doing it right better? This way lengthens telomeres. Doing it for performance actually shortens them because of the effect of cortisol with simultaneous insulin spikes. This is why aerobics and endurance exercise is deadly bad for longevity. So you need to decide what is really your goal. COntext matters huge in concerns like these. I am pretty clear where I come down on this equation. And before you even ask.......can you get ripped this way? Well, yes you can.....but it will take longer to get there and you will have decidely longer telomeres when you arrive. This is why performance athletes never seem to make it past 70 yrs old. They exhaust all their stem cells and turn their mTor pathways against themselves.
As a former distance runner who has seen the error of his chronic cardio ways (in terms of how chronic cardio is misaligned with longevity/health goals), I now use HIIT (running) with the aim of burning fat while not sacrificing lean tissue. Stated differently, my goal is fat burning while conserving muscle. And in terms of any serious choice between performance goals and health/longevity goals, I come down in favor of the latter at this point.
With this in mind: I completely get the logic of fasting after HIIT sessions, so as not to "turn off the fat burning peripherally." Can you say more about how long the post-HIIT fast should last? Implicit in my question is a concern that fasting for too long after HIIT sessions could shift the process from fat burning to muscle wasting. I should think that, for someone with goals such as mine, there would be an ideal/optimal window of time, post-HIIT, for fasting; after which time, the athlete oughta take some nutrition.
Let me add that I also get the bodybuilder's logic of eating quickly after a hard strength training session. It's the standard 4:1 carb/protein ratio where the aim is to kick up insulin so as to deliver the protein to cells (all that insulin production does serve muscle-building, but it seems with a hell of a cost to long-term health). And as someone who once seriously considered bodybuilding, and in fact trained for a short period, I can attest to the fact that most bodybuilders are serious eaters post-workout. And by and large, they tend to be some of the least healthy/fit humans around. Even the so-called natural bodybuilders. (To each his own. I respect that a bodybuilder's goals are different from longevity goals. What's sad is how few bodybuilders seem even to be aware of the distinction. In general they seem to subscribe to the mythos that big muscles are synonymous with fitness. And for what it's worth, I agree with the comment that very few bodybuilders seem to care much about cardio, and when they do it at all, they strongly line up in the long, slow distance camp.)
Anyhow: anybody got any thoughts about: given my primary health/longevity goals, and given that fat burning lasts as long as 96 hours post-HIIT, what's an optimal time window for fasting post-HIIT? FYI: