Re: calorie burn walk vs jog


Robert Grumbine wrote:
In article <uEDIg.73035$u11.23931@xxxxxxxxxxxxxxxxxxxxxx>,
Michael <news@xxxxxxxxxxx> wrote:
Although it was believed that distance determined the number of calories
burned, apparently new research has determined that running burns
50-100% more calories (depending on whether you're measuring total or
net calories).

Here's a link to an article by Amby Burfoot that explains this:

http://www.runnersworld.com/article/0,7120,s6-242-304-311-8402-0,00.html

Darn. Looks like I'll have to update what I tell people. But
it looks like a reasonable test.

Thanks for the info.


yes interesting article. But I have two comments about it:

First, I noticed the calorie count was still for both men and women
around 100.
(for men the average between 124 and 88 is 106,
and for women between 105 and 74 is nearly 90)
So to a first approximation, I think the 100 figure is okay.
But that's just because it is easy to remenber, and a matter of
opinion.
IOW always say 100 per mile with the added YMMV caveat

Second. I am not sure I agree with the Bouncing theory of the
difference between running and walking. In fact I was trying during
yesterdays run to figure this out and a Car Talk puzzler suggested the
answer. Consider a car going down the road. the portion of the tire
touching the road is travelling at what speed? Zero (it is touching the
ground and for that brief moment is not moving relative to the ground)
The portion of the tire on the exact opposite side of the wheel is
travelling at what speed? Well, twice the speed of the car, again for a
brief moment. Now that ignores all kinds of rotational movement, BUT
think about what happens to your feet and legs.

One leg is coming off the ground and moving backward. Your body (center
of gravity) is moving forward at some speed, so that leg as it comes up
must be accellerated not just to catch up to your body, but past it,
basically twice the speed of your body. After it gets in front, and
before it touches the ground again, the motion in that leg must be
decellerated and started to move backward.

Basically it is my contention that this continuous movement forward and
then backward of our legs is where the energy is burned.

The energy involved in moving the body, ie the center of gravity, is:
the energy to initially get the body moving horizontally
(no gravity involved here. this is a onetime cost cause bodies in
motion, stay in motion)
the energy to overcome wind resistance
(which is relatively small, even for sprinters)
the energy of moving the center of gravity up and down
(is small unless you have a Large bounce, but most runners learn to
run so the body stays level with little bounce)

Actually some wind resistance will be much higher on the legs since at
least postions of their motion involve moving forward faster than the
rest of the body (Hm: if a sprinter runs about 30miles per hour, is his
foot movuing forward at over 60MPH? wow!) So if the main energy cost is
overcoming wind resistance, then it's the wind on the legs that causes
the highest portion of this cost.

If there is a gravity component to the energy expeneded, then it is
that as we move our legs forward, we also raise them up. Does that move
our body (center of gravity) down? I would argue , no not much. While
we raise our back leg for the forward swing, we also extend our front
leg to ready for touching the ground. We don't get that extension for
free, because we don't let gravity straighten it out. (that might take
too long before we need to have our foot back on the ground.)

The basic premise was from musings during my run yesterday. Was I
dillusional, or does this idea have some merit?

Ed

.

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