Transcript Gordon Alderink - Determinants of human gait

Determinants of Human Gait: A Review
Role of Knee/Ankle Coupling in Stability, Control & Propulsion
Gordon J. Alderink, PT, PhD
Grand Valley State University
Cook-DeVos Center for Health Sciences
Grand Rapids, Michigan USA
Background
Dynamic Gait Perspective
Saunders and co-workers originally described six determinants (D1, D2, D3, etc) of
gait as precise movements by the pelvis, hip, knee and ankles that theoretically
minimized vertical and horizontal excursion of the body’s center of mass (COM),
thus, reducing the energy cost of walking. However, it has recently been
suggested that although these movements certainly occur, some of them may
play little or no part in optimizing energy cost. Furthermore, there is evidence
that a flattened COM trajectory increases muscle work and force requirements.
Proponents of the dynamic gait perspective suggest that an inverted pendulum
model of gait better explains the mechanical work and, therefore, metabolic costs
of walking.
Dynamic walking simplifies the study of gait and offers a constructive
perspective, i.e., yields predictions independent of experimental data. Since
the determinant model fares poorly, Kuo suggests examining an inverted
pendulum model:
Because of the complexity of human gait, mathematical models to describe or
simulate normal walking have been justifiably simplified. For example,
Saunders’s determinants of gait provide only a one-dimensional explanation of
how humans may control energy expenditure while walking. Since recent
evidence suggests that these gait determinants may not play a major role in
controlling energy cost, one might examine gait determinants from a different
perspective. Relevant to humanoid research energy cost may not be as
important to consider as propulsion and control (stability). Furthermore, we might
need to consider the interdependence of kinematic, kinetic and dynamic factors
with regard to energy cost and control.
3. Forced leg motion produces a trade-off in step-to-step transition costs vs
energy cost related to force production
1. The single support leg behaves like an inverted pendulum to transport the
COM with relatively little muscle force and work (much less than the gait
favored by the determinants theory)
2. Walking like an inverted pendulum requires a step-to-step transition, which
require work to redirect COM velocity
Kuo proposed a refined interpretation of the inverted pendulum gait using
muscular-driven models that can be described using four intervals of stance
phase (Figure 1).
Determinants of Gait
D1. Pelvic Rotation. Rotation of the pelvis about a vertical axis reduces the angle
of hip flexion and extension, minimizing the rise and fall of the hip joint, and,
thus, elevation of COM during a stride.
D2. Pelvic Obliquity. If the pelvis were to remain level during a stride, the rise and
fall of the hip joint associated with flexion and extension would force the trunk to
rise and fall as a function of the average elevation of both hips (stance and
swing). Pelvic tipping about an antero-posterior axis resulting in a downward
slope of the pelvis toward the swing leg reduces the cranial excursion of the
trunk.
D3. Knee Flexion in Stance. Early stance knee flexion effectively keeps hip height
constant, thus reducing the height of the apex of the COM.
D4. Ankle Mechanism. The apex of the COM is lengthened at initial contact by a
dorsiflexed ankle (1st rocker).
D5. Foot Mechanism. The leg is lengthened at the end of stance as the ankle
moves from dorsiflexion to plantarflexion (heel rise or 3rd rocker), thus reducing
COM vertical displacement.
D6. Lateral Displacement of Body. Slight physiologic knee valgus reduces the
walking base of support (BOS), thus minimizing side to side displacement of the
COM.
Kuo suggests that a flattened COM, as dictated by the six determinants, increases
the muscle work, force requirements, and, therefore, energy costs of walking.
Although the determinants do reduce COM excursion in a compass gait, Della
Croce et al., Kerrigan et al., and Gard & Childress concluded that most
determinants play little or no role in reducing COM and energy cost. Kerrigan et
al. demonstrated that only D5 optimized the height of COM. Baker et al.
suggested the optimization of energy expenditure during gait was not related to
lowering the COM, but related to maintaining phase relationship and relative
amplitude of the gravitational and kinetic energy of the body
The knee and ankle/foot are comprised of ~30 synovial joints with 6 DOF
movement. Each joint plays a unique interdependent role in the initiation and
maintenance of a stable, controlled, smooth efficient gait.
Movement is produced/controlled actively (muscle) and passively (joint morphology
& periarticular soft tissues). Muscle stiffness is controlled by its material and
active intrinsic properties, and reflexes (joint mechanoreceptors, GTO’s and
muscle spindles). Muscle actions account for 50% to 95% of the vertical ground
reaction force (GRF) generated in stance phase; GRF’s translate into relatively
high joint reactions forces, e.g., ~2.5 x BW at hip in single limb support. Physical
Stress Theory suggests that the human body will attempt to attenuate high joint
stresses.
Static (posture) and dynamic (gait) balance is provided by ankle/hip and
hip/knee/ankle strategies, as well as visual and vestibular input. During gait
“reflex” activity (at a metabolic cost) at the hip, knee and ankle control anteroposterior, and at the hip control medio-lateral, acceleration of the head, arms and
trunk, at the same time other essential kinematic events are taking place, e.g.,
joint motion, step length, toe clearance, etc.
Let’s also examine D3, D4 & D5 and muscle requirements, using the refined
inverted pendulum model proposed by Kuo (Figure 1):
From collision to rebound (~initial contact through loading response), the knee is
flexing as the ankle is plantarflexing. During this subphase hip and knee
extensors are main contributors early in stance, as are the ankle dorsiflexors.
Purpose
The purposes of this presentation are: 1) review the determinants of gait; 2) review
the dynamic walking perspective (inverted pendulum model); 3) review static and
dynamic postural/gait controls; and 4) consider knee/ankle coupling (D3, D4 &
D5) as crucial determinants for a stable, smooth dynamic human gait.
Role of D3, D4 & D5 in Stability, Control & Propulsion
Figure 1. Four subphases of stance illustrating instances of joint work and
trajectory of COM (Kuo A et al., Exerc. Sport Sci. Rev. 33 (2), 88-97, 2005).
Work is required to redirect the COM between pendular arcs so that positive
work is performed by the trailing leg before or simultaneous with negative
work by the leading leg. Metabolic cost depends not on COM displacement
per se, but on COM redirection between steps and the rate of work and
metabolic energy expenditure are related to step length and width.
With the inverted pendulum model sagittal plane passive dynamic properties
may provide stability. However, when more degrees of freedom are added
to the model significant active control may be needed to stabilize lateral
motion.
It can be argued that those utilizing a dynamic walking model (a compass gait in
itself) misinterpreted Saunders et al. explanation for a “relatively flat COM
trajectory.” Dynamic walking replaces one simple model with another one,
which certainly can produce complete gaits, but cannot model human gait
complexity. Muscle-driven forward simulations of normal and pathological
gait call into question the ability of simple dynamic models to characterize
gait. For example, muscle models incorporating force-length and forcevelocity properties of muscle can best explain static and dynamic biped
perturbations. Furthermore, dynamic simulations to perform muscleinduced segmental acceleration and power analyses have shown:
1) muscles do substantial work in raising the COM in early stance, and 2)
the interdependency of joint power transfers. Finally, one-, two- and threedimensional dynamic models, because of their simplicity, do not account
for the interdependent role of joint receptors, soft tissue controls
(ligament and muscle), and 6 DOF joint movements.
From rebound through preload (~midstance to terminal stance) the knee remains
extended as the tibia moves over the “fixed” foot (ankle dorsiflexion). The gluteus
maximus, vasti, soleus and posterior gluteus medius make substantial
contributions to knee extension, while the ankle plantarflexors provide primary
support in late stance and is a major factor in producing forward body
progression.
From pre-load through push-off (~terminal stance to preswing) the knee rapidly
flexes as the ankle begins to plantarflex. During this time period, the iliopsoas
and gastrocnemius are the largest contributors to peak knee flexion velocity
during double support. Apparently, the sartorius and gracilis can assist in
producing optimal knee angular velocity.
In conclusion, it appears likely that D3, D4 & D5 are important determinants to
control COM excursion, metabolic costs, joint stresses, and provide stability.
Robotic (humanoid) research might be furthered as a profound understanding of
the interdependent nature of human gait mechanics is realized.
References
1. Baker R et al., 8th International Symposium on the 3-D Analysis of Human Movement, 2004.
2. Della Croce U et al., Gait & Posture, 14: 79-84, 2001.
3. Ferber R et al., Gait & Posture, 16: 238-248, 2002.
4. Gard S and Childress D, Gait & Posture, 5: 233-238, 1997.
5. Gard S and Childress D, Arch Phys Med Rehabil, 80: 26-32, 1999.
6. Kerrigan C et al., Arch Phys Med Rehabil, 82: 217-220, 2001.
7. Kuo A et al., Exerc Sport Sci Rev, 33: 88-97, 2005.
8. Kuo A, Human Movement Science, 26: 617-656, 2007.
9. Magee D et al., Scientific Foundations and Principles of Practice in Musculoskeletal Rehabilitation, Saunders
Elsevier, 2007.
10. Mueller M and Maluf K, Phys Ther, 82: 383-403, 2002.
11. Piazza S, J NeuroEng & Rehab, 3:5, 2006.
12. Rose J and Gamble J, Human Walking (3rd ed.), Lippincott Williams & Wilkins, 2006.
While I concur that simple models can be constructive, they do not take into
account the multitasking nature of the integrated neuro-sensorymusculo-skeletal human that locomotes smoothly, while minimizing
physical stress, i.e., Physical Stress Theory, and metabolic costs.
Therefore, let’s examine, in a different way, three of the gait
“determinants.”
13. Whittle M, Gait Analysis, An Introduction (4th ed.), Butterworth Heinemann Elsevier, 2007.
14. Winter D, Gait & Posture, 3: 193-214, 1995.