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jscarruthers17
01-02-2008, 11:24 PM
The below may be of interest:
PHYSIOLOGY OF HUMAN RUNNING: FROM MOTORS TO FUEL PUMPS

Taken from:
_http://havemeyerfoundation.org/monograph.htm_
(http://havemeyerfoundation.org/monograph.htm)

A. J. Blazevich and N. C. C. Sharp
Sport Sciences, Brunel University, Uxbridge, UB8 3PH, UK

THE ELASTIC HUMAN
In order for a human to run quickly and efficiently for a given
period of time a number of physiological, biochemical and
biomechanical processes must be optimised. Human running is
accomplished by performing a series of bounces as gravitational
energy is stored in our `leg springs' during the leg shortening, or
impact, phase and is released during the leg lengthening, or
propulsion, phase (Fig 1). Approximately 0.6 J of energy are stored
and released per kilogram per bounce in the foot and calf (Ker et al.
1987), compared with about 1.1 J per kg in a 0.5 ton horse (Minetti
et al. 1999). The total energy stored and released in the whole leg
represents a substantial portion (about half in humans) of the energy
required to propel the body into the next step. Because the highly
elastic (ie high energy return) tendons are most responsible for this
spring-like behaviour, and their properties change in response to
loading, it is reasonable that some portion of training should target
the tendon..........

OPTIMUM MUSCLE CONTROL
The remaining energy required for running must come from muscle
contraction. It has been held traditionally that muscles lengthen, or
work eccentrically, during the impact phase of running and shorten,
or work concentrically, during the propulsive phase. Recent evidence
from human research, and experiments on animals, shows however that
muscles contract quasi-isometrically during the propulsive phase of
many stretchshorten- type movements (eg Kurokawa et al. 2003), or
during high-speed movements performed without a counter-movement
(Kurokawa et al. 2001). This makes sense when one considers the work
of Hill (1938), who showed that concentrically-contracting muscle
uses more energy than isometrically-contracting muscle, with the
disparity increasing as muscle force or length change (or velocity)
increased. As muscle power increases, the relative cost of performing
work by concentric muscle action increases, and the benefit of using
stored energy becomes greater.

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The spring in the arch of the human foot.

Nature. 1987 Jan 8-14;325(7000):147-9.

Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RM.
Large mammals, including humans, save much of the energy needed for running
by means of elastic structures in their legs and feet. Kinetic and potential
energy removed from the body in the first half of the stance phase is stored
briefly as elastic strain energy and then returned in the second half by
elastic recoil. Thus the animal runs in an analogous fashion to a rubber ball
bouncing along. Among the elastic structures involved, the tendons of distal leg
muscles have been shown to be important. Here we show that the elastic
properties of the arch of the human foot are also important.

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Jamie Carruthers
Wakefield, UK