I realy wish all the fats in foods were called lipids or something like that instead of fat because it causes a lot of confusion as we also call that blubber that accumulates around outr bodies fat too.[/quote]
It’s funny. People fail to realize that their cells are basically membranes, structural proteins and enzymes, and the membranes are all lipids.
The body prefers that the ultimate fat of dietary lipids be to a) fuel muscles and b) build membranes, while the primary fate of carbs is to be stored as fat unless glycogen stores are low. Of all your cells, muscle cells actually are best at using fatty acids.
Curious: How to muscles use fat as fuel? I thought they used glycogen, from carbs? [/quote]
So fatty acids are broken down in mitochondria (which are contained largely in red muscle fibers) by beta oxidation into NADH and FADH2 (which make ATP) and acetyl-CoA which is the same thing that sugar ultimately gets turned into, to enter the Kreb’s cycle.
So it makes ATP the same way really that glycogen does from oxidation, It does not however rebuild glycogen stores by that pathway. The thing about Glycogen is that it can produce ATP by glycolysis without oxygen (good for short bursts).
Keep in mind too that if you are not low on glycogen, all the carbs you eat basically get turned into triglycerides and stored as adipose, but the fats you eat typically enter muscle cells for beta oxidation which fuels by far most of your metabolic needs.
By the way, there may be a false assumption made that since weight training is high wattage (a 300 pound full squat by a 200 pound person performed in 1.5 second concentric is about 200-300 watts (about 150 plus “inefficiency”)) that it uses carbs. Not true. For up to about 10 seconds (maybe 1-6 reps) you are using almost only ATP and CP, and this gets replenished by fatty acid oxidation. Though Fred Hatfield said that ATP and CP gets used up within 1.5 seconds with a maximal squat. Still low rep strength training gets ATP and CP rebuild from fatty acids. The Russians firmly believed that sets of 2-6 reps were optimal for power, and that would only be true if CP and ATP stores were basically large enough to fuel those reps.
In fact this strongly suggests that the post workout window for carbs may not apply to pure strength training, because glycogen is probably not depleted at all in 1-3 rep sets. But if you do deplete glycogen by getting into the lactic acid zone then the glycogen can only rebuild by actively transporting glucose into the cell. Its hard to pin down just how long a set has to be to deplete glycogen because generally ATP and CP lasts for 1.5 to 6 seconds of full out work like sprinting or a single max squat, but when doing multiple reps there is little energy being used on the eccentric, and so its not like a full sprint. If you feel H-LA then you are depleting glycogen though.
Ridiculously good post man…thanks
edit: if I’m sprinting for like 12-13 seconds on a 100m sprint, and doing this several times (let’s say 10), thus putting me between 120-130 seconds over about a half hour window, does that mean I’m using carbs, as opposed to oxidizing fat for the energy needs by the end? I’m just confused about that part, because after I sprint I crave carbohydrates to the point that I can’t concentrate on anything until I get some. [/quote]
Yes, at 3 seconds of sprinting carbs have become the major power source, and at 6 seconds of sprinting you are pretty much having to use all carbs to replenish ATP as you continue, first by glycolysis, then Kreb’s cycle with oxygen. ATP has been depleted and your not giving a break that would let fatty acids do it alone-only with carb involvement can you keep up. Every extra second you run is going to use more carbs. And the glycogen will only be rebuilt by bringing more glucose into the cell. So each run will reduce glycogen a little more. [/quote]
Got it! And ultimately this is why people on Keto end up feeling miserable with this type of exercise, because the glycogen isn’t getting replenished?