In reply to i.munro:
> I think you overestimate the role of heat-reduction here.
> In Bouldering particularly the burst of activity tends to be far too short to affect body temperature at the time.
I think this sort of splits into two segments:
a) That the body can't react quickly enough during the act of climbing (in bouldering particularly) to cause a significange amount of sweat
There may well be some truth in this, although it's postulation either way. Interestingly, the study shows that the body is able to excrete sweat as a reaction very rapidly; modulating it for grip. Therefore I'm not sure it logically follows the body wouldn't start heat-reduction sweat similarly quickly. This also, obviously, becomes less applicable as we move to trad, sport, or even longer bouldering problems...
You mention later the "fear" aspect, which I'd not really considered, but looking back, there are certainly times on slabby boulder problems where I've been standing around for quite a while trying to commit to a move (yes, I sometimes struggle to commit to bouldering moves - a pad looks very small from a couple of meters up
). The longer you stand around, particularly in a position not of rest, your heart rate is going to be up and you're going to be getting hot. Which sort of leads on to...
b) Your "body temperature at the time" comment seems to imply that the body is starting from a point of normal temperature, heart-rate and sweat.
I don't think this reflects the average climbing session. The session is likely to start with at least some form of CV exercise, even if just the walk in to the crag. There is plenty of discussion on these forums on the need for a warm-up to reduce injury, and it would seem pointless to have "warmed up" and then allowed the body to return to cold again.
Anecdotally, I am certainly heavily panting at the top of, say, an 8-move boulder problem at my limit, so the body has obviously reacted to the lack of oxygen and is trying to supply the limbs already, the only part we don't know is the delay before the sweat kicks in, but speculate either way we can't know for certain without studying it.