Stephen A. Lawrence wrote:
I have one small nit to pick, which is that a soaring bird is not at all
equivalent to a bicycle "traveling downhill the whole way".
A soaring bird is taking advantage of wind shear to obtain ("free") energy
from the atmosphere, which can be used to travel in pretty much whatever
direction the bird wants. By soaring, birds (and sail planes, and, in
similar fashion, sailboats) . . .
That's true. I did not mean it quite so literally. I just meant that the
energy comes from outside the system, so this is not a fair comparison.
For that matter, the Olympic runners must run faster downhill than up. I do
not know how much faster. But the difference is nowhere near as large as it
is with a bicycle. In other words, most of the energy expended while
running is for "overhead" or mechanical friction in the body.
Bicycles have two giant advantages:
1. Low friction. Only a small amount of rubber meets the road, and the
friction from the chain and wheel bearings is very low. Automobile engines
produce far more friction.
2. Air cooling. Because he goes so much faster than a runner, a bicyclist
is cooled down by the headwind. This advantage was demonstrated
accidentally when researchers tried to test the athletic ability of the
famous bicyclist Eddy "Iron Man" Merckx in the 1960s. They hooked up probes
and had him ride a stationary bicycle in a clinic. He pooped out hours
earlier than normal, and he was covered with sweat. He was upset and the
researchers were baffled. It wasn't until later that everyone realized it
was because he was not being cooled by the usual 20 mph headwind.
A few experimental enclosed bicycles and pedaled aircraft have shields to
reduce air resistance, and eliminate this headwind. An athlete can go
faster on one of these, but over a long distance he will soon be covered
with sweat and weakened by an elevated body temperature. Sweat is an
inefficient, last-stage method of cooling the body. I believe the cooling
effect of sweat is enhanced when you wear a light cotton shirt, which
catches and holds the water near the skin rather than shedding it. Better
still to dump a liter of water over the shirt.
Contrary to the advice that has been often been published in recent years,
you should not drink a lot of water while running or bicycling intensely.
Apparently several people who died during marathons lately were killed by
drinking too much water (hyponatremia) rather than heatstroke or
dehydration as originally thought. The symptoms of hyponatremia and
dehydration are similar: "apathy, confusion, nausea, and fatigue." The
cause & treatment are exactly opposite but the symptoms look the same! I
think a little common sense would help: if you are not thirsty, do not drink.
- Jed
