from Ron Daniel:
Elaine's original question had to do with when is lifting an advantage.
Elaine asked me to give a description beyond the simple "faster turn over
and longer stride equals greater velocity" answer. As Elaine suspected, my
hypothetical description of the conditions that need to exist in order to
calculate what is necessary to have loss of contact result in faster
velocity has sparked some interesting discussion.
Please remember my hypothesis is for the race walker that is obeying the
straight leg requirement. Discussions that include bent knee walking or even
running is a change of topic.
My calculations do not require energy or force analysis. In fact I was
careful to say in the first part of my write up, ..."more difficult to
analyze are the forces and energy issues associated with race walking and
the potential changes when walking with loss of contact". In Jack T's reply
he astutely pointed out that to have a 4 inch float in 0.02 seconds would
require a velocity of 16.67 ft per second during those 0.02 seconds, which
is 50% faster than the base velocity of 11.11 ft per second that I used. By
pointing this out, Jack is taking the calculations to the next valuable step
in a performance analysis; that of setting parameters. Let's assume that
50% is above the upper bound for velocity in 0.02 seconds. Is 25%? Twenty
five percent is 13.89 ft per second requiring a float of 3.33 inches. In
fact, to maintain the velocity of 11.11 the float distance has to be 2.66
inches. At this point we have to accept that during a stride, the velocity
of the center of the body (not necessarily the center of mass) is not
If we are to model the movement and energy issues of a walker, we should be
careful to NOT arbitrarily constrain any of the attributes of the walker,
such as limiting ankle flexion to +/- 5 degrees.
In Ray Sharpe's reply, he is agreeing with my comments that in order to walk
with double contact or very nearly so, the walker must exert energy to
maintain that gait. Consequently, less energy is required when relaxing
from that effort and perhaps having more float.
The latter part of Wayne's reply, i.e. high stride frequency and push off,
leads to something valuable. With this observation we can examine exercises
that will improve the walkers strength in order to maintain push off through
a greater part of the stride while sustaining high stride frequency.
Let's keep up the useful banter.
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