THREE-DIMENSIONAL KINEMATICS AND KINETICS - Biomechanics and Motor Control of Human Movement - page 195

three moment components and their respective angular velocities:

P d = M xd ω xd + M yd ω yd + M zd ω zd (7.10 a )

P p = M xp ω xp + M yp ω yp + M zp ω zp (7.10 b )

where the moments are previously defined and ω xd , ω yd , ω zd , ω xp , ω yp , and
ω zp are the joint angular velocities at the distal and proximal ends (not
shown on Figure 7.3). The angular velocities are in rad/s, the moments are in
N ve the muscle

group concerned would be generating energy, and if they were - ve ,the
muscle group would be absorbing energy.

· m, and the powers are in W. If these products were +

7.4.5 Sample Moment and Power Curves
Figure 7.4 presents a set of intersubject averaged 3D joint moments at the
ankle, knee, and hip during one walking stride (Eng and Winter, 1995). Heel
contact (HC) is at 0% stride and toe-off (TO) is at 60%. Figure 7.5 shows the
3D power curves for these intersubject averages (Eng and Winter, 1995). The
curves are normalized relative to body mass; the moments are reported in N
·

m/kg and the powers in W/kg. Convention plots extensor moments in the
sagittal plane as positive; in the transverse plane, external rotation moments
are positive, and in the frontal plane, evertor moments are positive. A detailed
explanation of the specific function of each of these moments is beyond the
scope of this text; however, a few comments will be made on the larger or
functionally more important moments.

1. The largest moment during walking is seen at the ankle in the sagittal
plane. Immediately at heel contact (HC), there is a small dorsiflexor
moment to lower the foot to the ground; this is followed by a large
increase in plantarflexor moment reaching a peak at about 50% of stride
to cause the ankle to rapidly plantarflex and achieve an upward and
forward “pushoff” of the lower limb as the subject starts swing at toe-off
(TO) (see A2-S power generation burst in Figure 7.5).
2. The knee extensors are active at 8 - 25% of stride to control knee flexion
as the limb accepts weight (K1-S absorption phase), then the moment
reverses to a flexor pattern as a by-product of the gastrocnemic's contri-
bution to the increasing ankle plantarflexor moment. Then, just before
and after TO, a small knee extensor moment acts to limit the amount
of knee flexion in late stance and early swing (K3-S absorption phase).
The final burst of flexor activity just before HC is to decelerate the
swinging leg prior to HC (K4-S absorption phase).
3. The hip pattern is characterized by an extensor moment for the first half
of stance, followed by a flexor for the latter half. During the first half,
the extensors stabilize the posture of the trunk by preventing it from