Re: Kudu talk

On Feb 27, 3:42 pm, Marc Verhaegen <m_verhae...@xxxxxxxxx> wrote:
http://www.iht.com/articles/2007/08/15/healthscience/14swea.php

...

Sweat is our interior coolant, part of a uniquely human biologic machine.

Yep, need to sweat on the savanna.


(The author apparently has never head of sealions on land that profusely
sweat to cool down, see below.)

"uniquely human biologic machine" did you think Homo was a furry
sealion?



The machine drips and occasionally stalls: long waits on torpid platforms
can inspire glum reflections on how it will hold up as the planet heats up..
But experts counsel optimism: the system is sturdy, adjustable and even
reproducible by engineers working to make our future sweaty selves more
comfortable.
Humans operate in a tiny range of preferred internal temperatures. We can
tolerate overcooling, routinely recovering from long periods of hypothermia
with body temperatures diving 20 or more degrees below normal.
But we have little tolerance for even brief overheating: the brain
malfunctions with six or seven degrees of fever, and an internal temperature
of 110, barely a dozen degrees above normal, is often cited as the upper
limit compatible with life. So a good internal air-conditioner is essential,
both to dissipate the heat generated by the body's metabolism and to relieve
the heat absorbed from miserable summer weather.

Boy, if it's that bad out there, feel sorry for Mr. Kudu.

http://www.naturalhistorymag.com/master.html?http://www.naturalhistorymag.com/1206/1206_samplings.html
December 2006-January 2007

"Running Man Couch potatoes may disagree, but people are fairly well
built to run in the heat. We sweat more per unit of body surface area
than any other animal, and our upright posture exposes less body
surface to the sun than would walking on all fours, and more surface
to the cooling wind. On the hunt, those traits give people a distinct
advantage over most quarry. In fact, Australian Aborigines and various
Native American and African groups have traditionally practiced
"persistence hunting," chasing antelopes or other game in the midday
heat, often for hours, until the animals overheat and collapse."


(no problem)

Fur inhibits sweat-induced cooling, and furry animals generally have other
ways to lose heat. In humans, Dr.Jablonski argues, sweat glands evolved as
body hair vanished,

Tough luck for Mr. Kudu.


(Chimps & gorillas have sweat glands + fur.)

allowing optimal cooling of the enlarging hominid brain and an active
lifestyle even in the blazing sun.

(?? The first who ran the marathon droppepd dead.)

Probably was a couch potato.

http://www.nwemail.co.uk/unknown/viewarticle.aspx?id=795363
"THE recent Keswick/Buttermere round 34km road race is regarded as one
of the toughest running events in the country.
This year the race was won by Steve Littler, of Wesham Road Runners,
who set a new record time
of two hours, three minutes and 13 seconds - two minutes inside the
time set by Kenny Stuart and Jon Broxap in 1982.

Chris Steele, of Borrowdale Fell Runners, was second (2:10.18), with
Paul Waterston, of Morpeth Harriers, third (2:17.40).

First lady was Julie Carter, from Cumberland Fell Runners, (2:42.27)."

Wow, Julie Carter, a lady kudu runner.


For sedentary pursuits in temperate weather, people have no need to sweat:
excess metabolic heat easily moves from blood vessels at the surface of the
skin into the surrounding air. Because the skin is not completely
waterproof, some evaporation of water from skin cells adds a little extra
cooling.



But when the body's owner decides to exercise, the muscles generate too much
heat for the air to absorb. The same thing happens when the temperature
climbs into the 90s: the skin stops losing heat to the air and absorbs it
instead. Then temperature-sensing nerves in the skin and the body's interior
tell the brain to unleash a flow of sweat for heavy-duty evaporation and
cooling.

Looks bad for Mr. Kudu and couch potatoes.


Humidity reduces evaporation and makes everyone sweatier. A breeze enhances
evaporation and makes skin cooler (unless the air is so hot the body absorbs
its heat instead). Dehydration markedly reduces sweat production. So does
sunburn.
But individual sweat patterns still vary enormously. Age, sex, genes, weight
and shape play a role, said Craig Crandall, a thermoregulation expert at
University of Texas Southwestern Medical Center and Presbyterian Hospital,
both in Dallas. So does non-exercise activity, and so, according to a
pivotal set of sweat studies done during World War II, does clothing,
although not in the way one might predict.
Some people have fewer than 2 million sweat glands; some have as many as 4
million. Heavy sweaters may have glands 5 times average size; their big
glands are more sensitive to nerve stimuli and make more sweat.




(interesting)

Everyone's inner temperature cycles around a slightly different genetically
determined version of 98.6 set by the hypothalamus, the brain region that
serves as thermostat. We run a little cooler in the morning, a little warmer
in the late afternoon. Women run about half a degree higher after ovulation.
With menopause the female thermostat becomes notoriously trigger-happy,
imagining excess heat where none exists and generating unnecessary sweat.
Men may be more thermally stable, but not for long: beginning about age 60
both sexes sweat less, even if they are in good physical condition, and even
if they become seriously overheated. Thus the statistics that during heat
waves the elderly are at highest risk of heat stroke.
As for obesity, it is complicated, Dr.Crandall said. Fat may insulate the
interior from very hot external temperatures, but it also may compromise
heat transfer from interior to skin. Carrying more weight generates more
metabolic heat to get rid of. That means more sweat, but research suggests
that large people cannot grow more sweat glands to cope with the extra heat
load. Radiation of heat from skin to air may become especially important in
their heat control.

http://ws100.com/results07.htm
Scott Jurek, 2004, 15:36:27

Not too shabby, 100 miles in a little over 15 hours. This guy was no
couch potato.



(yes: "There are no fat animals on the savannah, with the exception of small
burrowing rodents or marsupials. In the case of these species, the fat is
brown rather than white, internal or localised (fat tail) rather than
subcutaneous and, unlike human fat, it is subject to seasonal fluctuation.
Among larger animals, the dromedary has occasional need of a fat store
against food shortage, but here again the fat is highly concentrated (in the
hump), varies with the animal¹s feeding condition, and fluctuates between
0.5 & 8 % of its body weight. The only +-fat animal which exploits the
grasslands around the rivers is the hippopotamus, but it does this at night
and stays in the water during the day. In the case of marine mammals,
however, the fat tissue is universal among the larger species. It varies
from 20 to 25 % of the body weight in fast swimmers to more than 40 % in the
slower species (Slijper 1958, 1979). The adaptiveness of this feature in
water has been further illustrated by studies of human athletes. For
example, blacks - in whom SC.fat comprises a somewhat lower percentage of
overall body weight than in other races - tend to be the swiftest runners
over both short and long distances, but they are relatively poor swimmers
(Ghesquiere & Bunkens). Successful swimmers are on average fatter than the
winners of track events, and many long-distance swimmers are even grossly
fat (Pugh & Edholm 1955). The fat layer has been shown to be an effective
barrier against heat loss in water. A study of a fat Channel swimmer
revealed that when lying still in bath water at 18°C for more than one hour,
he complained of no discomfort other than boredom, whereas another subject
with much less SC.fat complained of intense discomfort and showed a drastic
drop in rectal temperature after fifteen minutes (Pugh & Edholm).
Clearly, the possession of the fat layer facilitates spending more time in
the water. The result of one recent experiment even suggested that the
converse may also be true. It was found in a study of slightly obese women
that, without dietary restriction, an hour¹s daily walking or cycling
reduced body weight by 10 & 12 % respectively after 6 months, while a daily
swim caused a weight gain of 3 % over the same period (Gwinup 1987). On
land, OTOH, SC.fat has the dual disadvantage of reducing speed and, in hot
climates, of acting as a heat trap. An extra weight of fat tissue equivalent
to only 10 % of body weight seriously reduces speed. Even in temperate
climates, no terrestrial animal that has to run for its life - be it as
predator or prey - has much fat. Hares, eg, which escape predators by
running, have much less body fat than rabbits, which take refuge in their
burrows. Excess fat can constitute a real risk to humans taking exercise,
esp.in hot & sunny environments (Austin & Lanking 1986). In fact, it has
been calculated that most land-based sports other than walking and table
tennis are up to 10 times more likely to lead to fatalities than swimming,
despite the additional danger of drowning incurred by swimmers (Dolmans
1987). And the same fat layer that is advantageous in water, with its high
thermal conductivity, is a handicap to effective temperature control
on-land. Stranded dolphins, even in cool environments, soon die of
hyperthermia. And Pribilof fur seals are seriously distressed by any
activity on land at air temperatures of only 10°C (McFarland et al.1979:
773). The alleged danger of overheating on the savannah - sometimes advanced
as the reason for hairlessness - would have been compounded by the evolution
of the fat layer.")

...

"An estimated 5,000 children ages 14 and under are hospitalized due to
unintentional drowning-related incidents each year; 15 percent die in
the hospital and as many as 20 percent suffer severe, permanent
neurological disability."

National Safety Council

Don't forget to wear your lifejacket.
.