Tom, using your logic regarding reserve utilization, the minute a starter culture runs low on sugar in the wort, it begins using up its glycogen reserves. I don't think this is the case. The cells become dormant, their metabolism slows and the utilization of reserves is already minimized even without the further slowing by cold temps. I don't think viability or health is affected by a few hours at room temp in a beer environment, if it were then we wouldn't be harvesting viable yeast off the bottoms of fermentors after days of this kind of environment.
As the yeast detect the sugar is running low they actually generate more glycogen to build
their reserves. Once all of the sugar is gone and their ATP reserves are depleted they have to begin using the glycogen to generate more, there's really no other choice. Protein synthesis doesn't stop, even the process of flocculating requires protein synthesis. Living requires energy, and that's what the glycogen is there for. If you warm the yeast it will begin synthesizing proteins to help it survive in its present environment. If that environment is a warm spent starter then that is what the yeast will protect itself from, including generating ADH2 to begin using the ethanol as a carbon source. That will take energy. Unfortunately, ADH2 only converts ethanol to acetaldehyde (and it is specifically not synthesized in the presence of glucose). What you want when you pitch your yeast into beer is ADH1 to convert acetaldehyde into ethanol, the final step in the relevant fermentation pathway. So when you pitch your re-warmed starter into wort, the yeast have to generate ADH1 and at the same time remove the ADH2. And that is only one example, there are bound to be many more proteins that the yeast need to survive in a an ethanol solution as opposed to wort.
That being said, I'm not saying it is definitely enough to deplete all of their glycogen reserves or even to have more than a marginal affect, especially after just a few hours. But it seems pretty clear to me that from that perspective it is a step in the wrong direction. There may be benefits from pitching warm that offset it, I haven't tested that either.
As for harvesting after several days, there will be stronger cells and weaker cells and you can pitch a lot to make sure there is sufficient amount of healthy yeast. But that doesn't mean it's optimal to keep the yeast under beer.
Heat shock is a phenomenon that involves subjecting an organism to temps above its normal or optimal environment. Since a yeast's optimal temp is well above our typical fermentation temp, or even most room temps, I don't think we are going to find heat shock proteins being expressed in a culture pitched in a properly cooled wort.
My point about heat shock was in reference to your comment "if there is such a thing as shock", because there is such a thing as shock. But I may have misinterpreted what you meant. Anyway, I haven't read any research for differential expression when moving yeast quickly from cold to warm temperatures relevant to fermentation.
Bottom line, yeast is pretty tough stuff and I'm not sure there's a "best way" here thats head and shoulders above the others.
Agreed. I think Denny's point is that pitching cold works just as well and gives you one less thing to worry about on brew day.