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M Swanepoel
10-01-1998, 12:58 AM
Hello All, The discourse concerning the angular displacement/torque
characteristics of exercise machines is interesting. I am
suspicious of exercise machines that control both displacement
and load simultaneously - they must be physiologically
appropriate for a very small sector of the population, if anyone.
Unless performances on various exercise machines become
recognized competitive events, machines that do not offer the
athlete some freedom in the speed of muscle useage and contraction
versus displacement, cannot possibly be a good way to prepare the
body for competition?! It seems to me that many machines out there
are simply not designed by biomechanicists.

I have a more serious worry than this though. Dr Seedhom
of Leeds University and his PG students such as Drs Tony Swann and
Nelson Chen have investigated joint useage and degradation. Their work,
taken as a whole together with that of such workers as Drs Bullough
and Goodfellow of Oxford, and Kempson, demonstrates conclusively
that joints subjected to "heavy impacts", such
as the ankle, are relatively free from osteoarthrosis in old age, and
those that are subjected to much lower loading experience a greater
incidence of cartilage fibrillation and osteoarthrosis. In fact as
one progresses up the lower limb, from the ankle, to the knee, on to
the hip, and then to the lumbar apophyseal joints, so the extent of
fibrillation increases at any given age. The reason appears to be
that the cartilage of joints subjected to regular "peaky" loading
with relatively high joint contact stresses, is much stiffer and better
able to endure the odd exceptional load, than softer cartilage that is
lowly loaded. There are now many new exercise machines on the market
that are advertised as being "low" or even "zero" impact machines -
including one horrific device that subjects the lower limbs to
a centripetal acceleration about a fixed horizontal axis through the
hips, with the knees locked straight. My problem is that joint
cartilage and muscles subjected to such activities will certainly not adapt
appropriately for normal walking, running and stair climbing, and
that people using such unphysiological exercise devices may be
letting themselves in for serious joint trouble later in life.

The catch is that because the market for such devices is relatively
modern, we have no studies of the long-term effects of using them.
Should biomechanicists be setting up some sort of body that
investigates exercise machines, and award their "mark of approval" to
decent ones, while withholding their blessing from the bad? Should
biomechanicists not try to establish the long term effects of various exercise
machines using experimental and control groups?

Mark W Swanepoel, PhD
School of Mechanical Engineering
University of the Witwatersrand
Johannesburg
South Africa

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