View Full Version : Re: BIOMCH-L Digest - 30 Jan 1999 to 31 Jan 1999 (#1999-28)

Joan E. Bechtold
02-01-1999, 05:04 PM
Here's another installment in the ever-fascinating world of Biomech-L.

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Thomas A. Stoffregen wrote:
> > 1. Biomechanics in Space
> >
> >Date: Sat, 30 Jan 1999 05:37:20 -0800
> >From: Jack Sujovolsky
> >Subject: Biomechanics in Space
> >
> >Hello Group...Is anyone aware if any gait studies, including "GRF"
> >were conducted in space? I am curious as to the effect of an abscence
> >of gravity towards treadmill running...It is one of the exercises
> >prescribed in space. I was specifically thinking about the maintenance
> >of bone mass, which is triggered by the pounding our body takes...
> >
> >Jack Sujovolsky, MS
> Astronauts have run on treadmills while in orbit (beginning on Skylab, I
> believe), and the space agencies surely have reams of data on this.
> However, such running does not take place in the "absence of gravity".
> A little physics. In orbital flight there is gravity. The force of
> gravity is about 98% as strong for objects in low earth orbit as it is for
> objects on the surface. It is gravity that sustains orbital flight; if
> there were no gravity the spacecraft and its contents would move only in a
> straight line; i.e., away from earth into deep space. People and other
> objects are weightless in orbit not because of any absence of gravity, but
> because there is no resistance to the extant gravitational force. The same
> is true in the terrestrial environment; if you take away the resistive
> force (usually provided by the ground), then the object becomes weightless.
> Consider jumping. Stand and jump straight up. During the period that you
> are airborne you are, literally, weightless. The only difference between
> this weightless and that found in orbit is that the latter lasts longer.
> Note that in a plane or other aircraft the force of gravity is resisted by
> aerodynamic lift created by the wings; people in aircraft are not
> weightless (except during the upper peak of parabolic flight, which NASA
> uses to "simulate" weightlessness).
> You cannot run on a treadmill when you are weightless; pressing against the
> treadmill with your feet will cause your body to float away. Treadmill
> running is possible on orbit only if the body is restrained in such a way
> that the treadmill can resist the forces that you apply to it. This is done
> with bungee cords, typically. It is important to note that with this
> manipulation the runner is no longer weightless; they have weight
> proportional to the force applied by the bungees. It seems unlikely that
> the bungees apply a force equal to 1 g, and so on-orbit running probably is
> characterized by the body weighing less than its terrestrial weight. This
> might make for some interesting differences in running. But it is not
> correct, physically, mechanically, bio-mechanically, or otherwise, to talk
> about "running in weightlessness".
> Tom Stoffregen
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