What prompts this post is something that Kendrick wrote about the Parasympathetic and Sympathetic nervous systems - two systems that are antagonistic to one another.
The Sympathetic NS gears you up for flight or fight. Your heart rate increases, blood flow is redirected to muscles, the liver releases glucose pushing up blood-sugar levels and various blood clotting factors are released in to the blood stream. This is a 'catabolic' state and is just what you need when faced with either conflict, or significant exertion (such as exercise).
The Parasympathetic NS offers opposing actions, slowing your heart, stimulating insulin and the release of bile, and redirecting blood to the gut to aid digestion. An 'anabolic' state that is perfect when you are ready, as Kendrick notes, 'to eat, digest and store energy'.
This is the point where Kendrick really caught my attention. He looked at these two states and considered the following,
- "...if you were stressed, and then tried to eat, your metabolism would be thrown in to confusion. You would be commanding the neurohormonal system to activate catabolism and anabolism simultaneously. This would mean high levels of adrenaline and cortisol, battling against high levels of insulin. Adipose tissue would be under instructions to both absorb and pump out fats in to the bloodstream. At the same time, the liver would be trying to store, and release, glucose.
With food inside them, your guts would be automatically switched to 'absorption'. But the sympathetic system would be fighting to direct blood away from the guts to the muscles. Wherever you looked, a fight for metabolic supremacy would be going on. Perhaps the most important battle would be for control of blood-sugar levels, a battle ending up with 'spikes' of blood sugar - as insulin tried, and most likely failed, to overcome the effects of the stress hormones surging about in the bloodstream." (Kendrick, 2007, pp214-215)
This mandates an approach that Art Devany has been pushing for some time. He has recommended both fasted training and (fasted) post-workout walks to allow optimal adaption (I think he once phrased it as 'bathing in an exercise-triggered hormonal wash'):
- The best thing to do after a work out is to take a 40 minute walk. During this walk you will burn fat because you have released growth hormone and your body is using free fatty acids to restore the phosphates and glycogen in your muscles. If you block that process by consuming anything that contains simple carbohydrate (and all sports drinks, energy bars, and liquid protein supplements do) you will shut down this fat burning process.
- "...the problem is 2 things happen: you're taking in foods that create an insulin spike, so that shuts down the growth hormone response that you induced in your workout. That's very important.
Insulin is basically antagonistic to growth hormone. So, the high glycemic load, the protein shake, even protein elicits an insulin response. So, you're shutting down one of the adaptive hormones that's intending to increase through the workout, and that's growth hormones.
The other thing is that you're shutting down gene expression, because muscle gene expression occurs in response to signals you've created. One is the intensity of the workout and then mitogen-activated protein kinases send signals to the muscles to begin rebuilding. And 2, that gene expression takes place best in a glycogen-depleted muscle.
So, if you replenish the glycogen immediately or quickly, you shut down gene expression that's remodeling the muscle that you intended to train.