Re: Influence of weather on calories burned? - Cycling Mob: Road Cycling, Mountain Biking and More

04-01-2004, 01:56 AM

In article <fIBac.4672$[Only registered and activated users can see links. ].worldnet.att.net>,
"AustinMN" <[Only registered and activated users can see links. ]> wrote:

> Van Bagnol wrote:
> > But when you're pedaling, you're _generating_ heat (some 70-75% of the
> > calories burned goes toward heat production rather than mechanical
> > energy), so your body has to work slightly less on cooling (sweating,
> > vasodilation) in colder weather. Air density is greater, though,
> > increasing wind resistance a little, so you'd have to work slightly more.
>
> I doubt the body burns calories to cool off. All it has to do is turn on
> sweat glands and open (relax) surface capillaries.

My point was to address the assertion that "the body's thermal regulator
has to work harder to keep your temperature up." While that would be the
case for a sedentary body in cold weather, as it would have to activate
brown fat deposits and initiate shivering to generate heat, for an
active body in cold weather, the activity itself is already generating
quite a large amount of heat, obviating the need to shiver at all.

The effort required (the word "effort" and my earlier choice of "work"
are misleading terms, I admit--how about "demand"?) for cooling is less,
because the environment is already cold. And although it's debatable
whether the body "burns" calories to cool off, dilated capillaries do
reduce blood flow resistance, causing circulation and heart rate to
increase. (Warmer weather tends to increase heart rate for the same
amount of mechanical exertion.) Secondly, the body does "burn" (expend)
more resources on cooling, in the form of depleting its water inventory
for perspiration.

Van
--
Van Bagnol / v b a g n o l at earthlink dot net / c r l at bagnol dot com
....enjoys - Theatre / Windsurfing / Skydiving / Mountain Biking
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