Glycogen-Free Muscle Growth - Erratum: Differences in P70K-Phosphorylation Between Glycogen De- and Repleted Leg Even Less Significant Than Previously Reported.

Image 1: For the SuppVersity Super-Student Duong Nguyen, training in the semi-fasted state worked wonders. Want to know more? Read his guest-post and visit his blog.

This is post #713 and another premier. It's the first time that I have to go back (at least partly) on something I posted three weeks ago in a post about the myth that well-stocked muscle glycogen stores would be necessary to induce an anabolic growth response in skeletal muscle. Those of you who read the respective blogpost probably remember that I had to rely on the little information there was in a short abstract that had been published in the program of the 2011 ISSN conference, because a full paper with all the information on the study had (and still has) not been published.

Now, three weeks and a long and interesting email-correspondence with the author, Donny Camera from the RMIT University in Melbourne, Australia, later, I have to admit that (my interpretation of) the abstract was not completely correct. In the abstract it says (Camera. 2011):

p70S6K^Thr389 phosphorylation in LOW [glycogen depleted leg] increased in both nutrient (15-49 fold) and placebo (∼8 fold) groups 1 h and 4 h post-exercise compared to rest (P <.05) but was only different from rest 1 h post-exercise in NORM in the nutrient group (∼36 fold, P <.05).

Back then (and to be honest, even now that I know what Donny actually meant), my understanding of "but was only different from rest 1h post-exercise in NORM in the nutrient group" was that there was no additional benefit from exercise in the normal leg, unless a post-workout drink consisting of 20g Whey + 20g maltodextrin was consumed. While I found that initially surprising I assumed that the absolute p70S6K response (remember the abstract provides information about the relative changes, only) in the non-depleted leg [NORM] would have been much higher than in the glycogen depleted leg, so that the addition of a protein + carbohydrate post-workout shake would not really make a difference.

Figure 1: This graph depicting the p70k response in the glycogen depleted and the normal leg is of merely illustrative nature the data is not identical with the original material from the study (Camera. 2011), but was made up to adequately represent the most important findings.

Now, that I have the absolute data available, I see that this is not the case (cf. schematic illustration in fig. 1). The absolute p70S6K response to exercise was within the statistical margin of error identical in both groups regardless of whether post-workout nutrients were or were not supplied. Still, the addition of the whey + maltodextrine combination increased the p70S6K response in the "anabolic" 1h window roughly 4-fold above the increase that was seen with exercise alone. In that, the increase in the NORMAL leg may have been greater; more importantly, however, the maximal degree of phosphorylation at t=1h post exercise was identical in both legs. Furthermore, the absolute data underlines the aforementioned importance of post-workout nutrient supply (in this case in the form of fast digesting protein + carbohydrate sources), as the provision of the whey + maltodextrine formula quadrupled the already pronounced increase in p70S6K phosphorylation irrespective of the glycogen status of the trained leg.

Thus, it turns out the relative values from the abstract, on which I based my previous blogpost, did provide an initial impression, but not the whole picture oft what happens on the cellular level when you train a "fasted muscle" (which is why I usually do not even bother with abstracts, if I do not have access to the full text, but in this case, there simply was no fulltext, and the results were too interesting to keep them back). Contrary to the researchers initial hypothesis was there not only more than enough "gas in the tank" of the LOW leg even after selective glycogen depletion to for the protein synthetic cascade to be put into motion, the absolute degree of p70S6K phosphorylation and (this is only a reasonable assumption) exercise and nutrient induced protein (re-)synthesis were also identical.

Image 2: Glycogen stores (magenta staining) in liver cells (A. Gunin)

Did you know that the rate of glycogen depletion in the human liver upon fasting (no exercise) is about 0.3mmol/kg liver tissue per minute? If we assume that, in a fed state, the average human being stores roughly 300mmol/kg glycogen in his/her liver, a 16-hour fast, as Martin Berkhan from leangains.com suggests them, would use roughly 96% of your liver glycogen stores (calculations based on Nilsson. 1973) - probably no coincidence that we are seeing the first detrimental effects on resting energy expenditure after this time-span, what do you think?

Personally, I was not surprised by this result, partly because I still think that this way of selective glycogen depletion is not representative of whole body starvation, the one and only state of which I would assume that you would see profound decreases in the anabolic response to exercise. And since I know you would be asking: I assume you will see identical results if you train (intermittently) fasted (and Duong is the living testimony to this hypothesis ;-), although your whole body (and especially liver) glycogen levels will probably be lower than the ones of the study participants.