BIOMECHANICAL MOVEMENT SYNERGIES - Biomechanics and Motor Control of Human Movement - page 289

τ (sec)

0

*Peak R xy = − 0.677 − 1 − 0.5

−

0 0.5 1

0.2

at T = 0.16 s

− 0.4

12

− 0.6

10

*

− 0.8

8

6

R Glut Med
L Glut Med

4

2

0

0 10 20 30

Time (sec)

40 50 60

Figure 11.5 A 60-sec linear envelope record of the left and right gluteus medius
muscles showing a synergistic reciprocal pattern. R xy (upper right) is plotted for τ =

± 1 sec and showed a peak of - 0.677 at τ = 0 . 16 sec showed these left and right
muscles were virtually out of phase, indicating a synergistic load/unload pattern. See
the text for more details on the reported low back pain of those subjects exhibiting this
pattern.

11.3 DYNAMIC BALANCE DURING WALKING

11.3.1 The Human Inverted Pendulum in Steady State Walking
During the gait cycle, there are two periods of single support (each about
40% of the gait cycle) and two short periods of double-support when both
feet are never flat on the ground: the heel contact foot is about 20 ◦ from the
horizontal and is plantarflexing rapidly toward a flat foot position, while the
pushoff heel is well off the ground and weight is entirely on the metatarsals
and toes. When we examine the trajectories of the COP under the feet and the
COM of the total body, we see the challenge to the human control system and
more specifically the human as an inverted pendulum. Figure 11.7 plots the
COP and COM of the body during two steps to illustrate this challenge. The
first observation is that the COM never passes within the base of the foot;
rather, it moves forward passing just medial of the inside of each foot. Thus,
during each 40% single-support period (LTO to LHC and RTO to RHC) the
body is a single-support inverted pendulum and its horizontal acceleration