MECHANICAL WORK, ENERGY, AND POWER - Biomechanics and Motor Control of Human Movement - page 158

1.29
1.28
1.27
1.26
1.25
1.24

1.7
1.6
1.5
1.4
1.3
1.2

Time

Figure 6.13 Plot of vertical displacement and horizontal velocity of HAT shows evi-
dence of energy exchange within the upper part of the body during gait.

position, HAT picks up velocity at the expense of a loss in height. Evi-
dence of energy exchange should be seen from a plot of the horizontal
velocity and the vertical displacement of the center of gravity of HAT (see
Figure 6.13). The potential energy, which varies with height, changes roughly
as a sinusoidal wave, with a minimum during double support and reaching a
maximum during midstance. The forward velocity is almost completely out
of phase, with peaks approximately during double support and minima during
midstance.
Exchanges of energy within a segment are characterized by opposite
changes of the potential and kinetic energy components. Figure 6.14 shows
what would happen if a perfect exchange took place, as in a swinging
frictionless pendulum. The total energy would remain constant over time in
the presence of large changes of potential and kinetic energy.

Simple Pendulum

Total Energy

Potential
Energy

Kinetic
Energy

Time

Figure 6.14 Exchange of kinetic and potential energies in a swinging frictionless
pendulum. Total energy of the system is constant, indicating that no energy is being
added or lost. (Reproduced by permission of Physiotherapy Canada .)