Other/Mixed Fasting and Heart Rate (A+A training)

[Snowman]

As I've been moving through Al's Plans 103 and 104c, I've also been doing intermittent fasting on some days. For the most part, I've only fasted on days that I haven't trained, but occasionally I've trained at the end of a fasting period. Since it is alactic/aerobic training, I don't worry about blood sugar issues. This usually happens when I train at the middle/end of the day, and I'll just keep my prior food intake to a minimum, train, and then eat right afterwards. Anyways, to get to the point, I have noticed a consistent pattern emerge when training at the end of a fast.

My power output remains the same (as far as I can tell), I perceive the training as more difficult (though only slightly), and my heart rate is higher. To be more specific, my maximum HR is only about 5 bpm higher, and my minimum HR is about 10 bpm higher, meaning the gap between the two becomes smaller. I'm curious regarding peoples' thoughts on why this is, as well as any pros/cons of training this way.

My thoughts are as follows:
WHY
-I have heard that fasting stimulates the sympathetic nervous system (or that is simply 'under' stimulates the parasympathetic), which means I already have one foot in the boat of being a little uncomfortable and having a high HR thanks to my relatively spun up sympathetic system.
-At the end of a fast my glycogen levels may be a little low, and since even an A+A protocol uses glycolysis a little, my body may be 'freaking out' a little (there's probably a better way to phrase that) as I dip into my already low glycogen stores.
PROS
-I'm training my body to operate at a higher level of performance in a sub-optimal state, as well as training my mind that it's ok to feel that way.
-Since I'm already in a predominantly fat burning state and (maybe) have low glycogen stores when I start the session, I'm encouraging my body to utilize fatty acids instead of glucose when it's in an aerobic state.
-Perhaps I'm stimulating my body to produce more mitochondria as I impose physical demands on it while in a state that is not conducive to glycolysis. This might be stretching it.
CONS
-If I am over-stimulating my sympathetic nervous system, I could actually be stimulating a greater use of glycolysis, which could potentially run counter to my goals of increasing my aerobic capacity.
-It makes me sweat more and makes a not-particularly-comfortable experience marginally less comfortable.

Those are my thoughts, not all of which are founded in a solid understanding of the science. I would especially like to hear what people think about that first point on the cons list. I should note that my HR still remains below the ceiling of my MAF aerobic training zone throughout the fasted sessions.

 

[Steve Freides]

@aciampa

 

[Al Ciampa]

I need to write a basic description of the energy systems to sticky...

Glycolysis feeds aerobic metabolism. It is not something that kicks on only when movement gets intense. I think the terms "anaerobic" and "aerobic" confuse people. A+A uses glycolysis A LOT... what it does not use is anaerobic, non-mitochondrial ATP production.

It uses anaerobic, alactic ATP production to fuel the work; then, mitochondrial ATP production (which includes glycolysis tearing down sugar to pyruvate and feeding it into the Krebs cycle) restores the primary substrate of anaerobic, alactic ATO production: phosphocreatine (PCr). Repeat for the entire session.

So, low glycogen levels do effect A+A training to some degree, and it could contribute to a higher resting HR, through various mechanisms (i.e, the brain is asking for sugar?).

SNS is no doubt a major player; as is hormonal environment while fasting. SNS will stimulate a greater use of.... "non-mitochondrial lactic ATP production" (not, "more glycolysis"), which will increase HR.

Your concern of the 1st con bullet: it depends upon your state of health and other stress in your life. But you are likely not shooting yourself in the foot.

 

[Snowman]

Glycolysis feeds aerobic metabolism

I should have been a little more specific and differentiated between glycolysis as a stand alone process and that which feeds into the Krebs cycle (I get a bit tunnel vision-y sometimes). My thought is that, while fasting, perhaps most of the acetyl-CoA comes from fatty acids, so beta-oxidation as opposed to glycolysis. When I refer to glycolysis in the original post, I'm referring (as you surmised) to stand alone glycolysis, ultimately producing lactate as opposed to just pyruvate.

as is hormonal environment while fasting

Ah yes, I didn't even think about that. I guess I SNS stimulation would definitely change hormone levels, though.

you are likely not shooting yourself in the foot.

That makes me feel a little better. I'll just keep telling myself that I'll be fine as long as my HR stays below 160 or so...

 

[Al Ciampa]

To my limited knowledge, it is hormone action that stimulate SNS activity. Could be other mechanisms as well.

Yes, it is all inclusive just to see your HR low. If you are not in ill-health, fasting is fine, even a great thing.

 

[banzaiengr]

I thought I used to understand "aerobic" and "anaerobic" and the krebs cycle until Protocol 102 and by 103 I was completely blown out of the water. Now I just hope I wake up in the morning.