1. ASB Symposium: Modern Perspectives on the Six Determinants of Gait
Speakers: C. T. Farley, D. S. Childress, D. C. Kerrigan, A. D. Kuo (chair)
In 1953, Saunders, Inman, and Eberhart does not reduce the mechanical work mov-
proposed that six kinematic features—the ing the center of mass, and it actually in-
Six Determinants—were employed to re- creases the metabolic cost.
duce the energetic cost of human walking.
These Determinants have long been featured When Some Gait Determinants Fail,
in many clinical textbooks, and are consid- Some Equations Can Eventuate
ered a major paradigm for understanding Dudley S. Childress, Steven A. Gard, and
gait. But like all successful scientific theo- Steven Miff
ries, the Six Determinants have been subject Rehabilitation Engineering Research Center
to rigorous testing and refinement. In this on Prosthetics and Orthotics,
symposium, four speakers will reexamine Feinberg Medical School, Northwestern
this paradigm from clinical and/or scientific University, Chicago, IL
perspectives, and offer modern interpreta-
tions of this important theory. The six determinants of gait proposed by
Saunders, Inman and Eberhart supposedly
Flattening the Center of Mass Trajectory reduce peak-to-peak vertical motion of the
Increases the Cost of Walking torso during walking compared with their
Claire T. Farley and Justus Ortega compass gait model. Gard and Childress
Dept. of Kinesiology and Applied Physiol- have shown that pelvic obliquity and stance
ogy, University of Colorado, Boulder, CO phase knee flexion, the 2nd and 3rd deter-
minants, do not reduce this peak-to-peak
This talk focuses on the hypothesis that movement. Consequently, the determinants
minimizing the vertical movements of the are questioned. If the idea about what the
center of mass will reduce the mechanical determinants do is not valid, the measured
work and metabolic energy consumption of peak-to-peak movement should be approxi-
walking. Subjects walked normally and with mately the same as predicted by a compass
minimal vertical excursions of the center of gait model with a rocker foot. This approxi-
mass (i.e., ‘flat trajectory walking’). Flat tra- mation allows us to write an equation that
jectory walking led to impaired inverted predicts peak-to-peak vertical movement is
pendulum energy exchange. Consequently, proportional to walking speed, which has
although the mechanical work required to been observed. Another equation eventuates
lift the center of mass was reduced by nearly from differentiation to predict that peak-to-
75%, this reduction was offset by the extra peak vertical acceleration is proportional to
work needed to accelerate the center of mass the square of the walking speed (over a lim-
in the second half of stance. For these rea- ited region). Preliminary data tends to sup-
sons, the mechanical work of flat trajectory port the theory. Failure of several of the de-
walking was not lower than in normal walk- terminants is required in order for the theory
ing. Surprisingly, during flat trajectory to be developed.
walking, subjects consumed approximately
twice as much metabolic energy to travel a
meter as during normal walking. We con-
clude that minimizing the vertical excur-
sions of the center of mass during walking

2. The Heel Rise Determinant of Gait Mechanistic Determinants of the Ener-
D. Casey Kerrigan getic Cost of Walking
Department of Physical Medicine and Reha- A. D. Kuo
bilitation Depts. of Mechanical Engineering & Bio-
University of Virginia School of Medicine medical Engineering, Ann Arbor, MI
Although the determinants of gait described Muscles consume energy when performing
by Saunders and Inman recently have been mechanical work, and also when producing
challenged, our group's data do agree with mechanical force even without work. The
Saunders and Inman's report that the actual metabolic cost of walking might therefore
vertical displacement of the center of mass depend more directly on kinetic, rather than
during walking is reduced to some portion kinematic, features. A mechanistic approach
of that predicted using a compass based to walking, based on the physics of an in-
model. Saunders and Inman had described verted pendulum, shows that relatively little
this reduction in actual versus predicted ver- work is needed to produce the inverted pen-
tical center of mass displacement as being dulum motion. But substantial work is
due primarily to three phenomena or deter- needed to redirect the body center of mass in
minants of gait; pelvic tilt, pelvic rotation, the transition between inverted pendulum
and knee flexion in stance, although Gard phases. We will show that this determines a
and Childress effectively disproved two of substantial fraction of the metabolic cost of
these determinants (pelvic tilt and knee flex- walking. In this mechanistic approach,
ion) and we disproved another (pelvic rota- metabolic cost depends not on center of
tion). In search of an alternative explanation mass displacement per se, but on center of
for the reduction in actual versus predicted mass redirection between steps. The overall
center of mass displacement, we explored metabolic cost of walking appears to be a
the phenomenon of heel rise at the end of result of the tradeoffs between this work,
stance of the trailing limb. We modeled the and the costs of moving the legs and sup-
effect of measured heel rise during normal porting body weight.
walking on raising the center of mass while
the center of mass is at its lowest point dur-
ing the gait cycle. We found that this mod-
eled effect of heel rise on center of mass po-
sition accounts for most, if not all, of the
overall reduction during gait in actual versus
predicted center of mass vertical displace-
ment. We conclude that while indeed there
is a reduction in center of mass displacement
compared to that predicted with a compass
gait model (as originally described by Saun-
ders and Inman), this reduction can be
largely, if not entirely, explained by the
phenomenon or new determinant of heel rise
occurring at the end of stance, which in turn,
may be attributable to foot/ankle anatomy as
well as ankle/foot muscle control.