THREE-DIMENSIONAL KINEMATICS AND KINETICS - Biomechanics and Motor Control of Human Movement - page 198

flexing forward under the influence of a large posterior reaction force
at the hip; this also assists the knee extensors in preventing collapse
of the knee joint and, in addition, contributes to forward propulsion
by what has been described as a “push from behind” (H1-S generation
burst). The flexor moment during the second half of stance serves two
functions: first, to stabilize the trunk posture by preventing it from
flexing backward under the influence of the forward reaction force at
the hip; second, in the last phase of stance and early swing (50 - 75% of
stride), to achieve a “pull-off” of the thigh into swing (H3-S generation
burst).
4. The major transverse activity is at the hip. During the first half of stance,
the external rotators of the stance limb act to decelerate the horizontal
rotation of the pelvis (and trunk) over the stance limb (H1-T absorption
phase); then, during the second half, the internal rotators are active to
stabilize the forward rotation of the pelvis and swing limb.
5. The frontal plane moments at the stance hip are a strong abductor pat-
tern to prevent drop of the pelvis (and entire upper body) against the
forces of gravity, which are acting about 10 cm medial of the stance hip
(H1-F absorption phase as the pelvis drops, followed by H2-F and H3-F
generation phases as the pelvis, trunk, and swing limb are lifted to help
achieve a safe toe clearance during swing). It is interesting to note a
similar moment pattern at the stance knee, but this is not as a result of
muscle activity. Rather, it is the response of the weight-bearing knee to
the large gravitational load; the knee tries to invert but the passive load-
ing of the medial condyles and unloading of the lateral condyles creates
an internal abductor moment. Such an example illustrates the fact that
internal skeletal and ligament structures can aid (or in some cases hin-
der) the activity of the muscles. Rehabilitation engineers involved in
prothesis design must be aware of the internal moments created by the
springs, dampers, and mechanical stops in their design.

7.5 SUGGESTED FURTHER READING

D'Sousa, A. F. and V. J. Garg. Advanced Dynamics Modeling and Analysis

(Prentice-Hall, Englewood Cliffs, NJ, 1984).
Greenwood, D. T. Principles of Dynamics , 2nd edition . (Prentice-Hall, Englewood
Cliffs, NJ, 1988), Chapter 7.
Zatsiorsky, V. M. Kinetics of Human Motion (Human Kinetics, Champaign, IL, 2002).

7.6 REFERENCES

Davis, R. B., S. Ounpuu, D. Tyburski, and J. R. Gage. “A Gait Analysis Data Collection
and Reduction Technique,” Human Movement Sci. 10 :575 - 587, 1991.