Transcript Document

BIOMECHANICS OF PLANNED GAIT TERMINATION
Joe Lynch, MSc and D. Gordon E. Robertson, PhD, FCSB
School of Human Kinetics, University of Ottawa, Ontario, Canada
Introduction
Ambulation is a basic necessity for human independence. People must
be able to start, maintain and then finally terminate their gait safely.
Problems arise when people who are elderly, disabled or have
neurological disorders cannot safely terminate their gait (O’Kane et al.,
2003). Some studies have focused on EMG and kinematics to describe
gait termination but the purpose of this study was to quantify the joint
kinetics during planned gait termination.
Results and Discussion
The trail leg’s (Figure 2) main goal in gait termination was to bring the trail
leg parallel with the lead leg while dissipating any remaining forward
momentum. To accomplish this, the trail leg’s moments of force acted
similar during the penultimate step to what they do during normal gait. The
dorsiflexors acted briefly to control foot-slap after terminal heel-strike,
followed by negative and then positive work from the plantiflexors. The
knee flexors acted eccentrically but briefly after heel-strike followed by a
positive period during midstance. The knee extensors then worked
eccentrically to reduce the rate of knee flexion. At the hip, the extensors
initially performed positive work to extend the leg then the flexors dissipated
energy during midstance and switched to positive work to cause swing
through.
During the swing phase and terminal step, little work was done by the
ankle plantiflexors during the placement of the trail leg in the final quiet
stance position. During swing, the knee flexors controlled extension prior to
the final HS before quiet stance while the hip extensors acted isometrically
to stiffen the hip.
During the final step the knee extensors produced a small amount of
work to straighten the leg while the hip flexors worked isometrically to hold
the hip from collapsing while the ankle plantiflexors did a similar job at the
ankle.
Discussion
Figure 3 shows data from the same subject’s lead leg during planned
gait termination. The lead leg arrived first at the quiet stance position. It
had the greatest changes from normal walking of the two legs. Its
termination process began with a brief dorsiflexor moment that controlled
foot slap, followed by two bursts of negative work by the plantiflexors and
no positive work as is the usual case during walking. The knee
extensors performed a burst of negative work immediately after heelstrike. This burst was briefer than the ankle plantiflexors and therefore
dissipated less energy. The hip flexors provided additional energy
dissipation.
As expected the ankle plantiflexors acted isometrically during quiet
stance while the knee moments of both legs were essentially inactive. In
contrast, the hip flexors acted isometrically to hold the hip in a slightly
extended position, which differs to what occurs during initiation of gait
when the extensors are active in preparation for forward motion.
Figure 1. Laboratory setup and stopping position for subjects
Methods
Eighteen subjects (9 female, 9 male) participated in the study. Subjects
were asked to walk five times with a natural cadence and come to a stop
on two side-by-side force platforms (Kistler). A third force platform
quantified the penultimate step. The forces and motion data were
collected using a Vicon MX system with 6 MX13 cameras. Figure 1
shows the walkway layout. The kinematic data were combined with force
platform data by inverse dynamics to determine the net moments and
powers at the ankle, knee and hip in both trail and lead legs using
Visual3D (Robertson et al., 2004). Moment powers were calculated by
multiplying the net moments of force times the joint angular velocities.
Data were ensemble averaged and normalized to body mass for
intersubject comparisons. Data were analyzed for one second before
and for two seconds after lead leg heel-strike (HS).
Figure 3. Mean angular velocities (top), moments (middle) and powers
(bottom) of the lead leg ankle (left), knee (middle) and hip (right) of an
exemplar subject. The vertical blue line indicates trail leg penultimate
HS; black line indicates lead leg heel-strike; and red line indicates trail
leg final HS.
References
Figure 2. Mean angular velocities (top), moments (middle) and powers
(bottom) of the trail leg ankle (left), knee (middle) and hip (right) of an
exemplar subject. The vertical blue line indicates trail leg penultimate
HS; black line indicates lead leg heel-strike; and red line indicates trail
leg final HS.
Biomechanics Laboratory
O’Kane FW, McGibbon CA, Krebs DE. Kinetic analysis of planned gait
termination in healthy subjects and patients with balance disorders. Gait &
Posture, 2003;2:170-9.
Robertson, DGE et al. Research Methods in Biomechanics, Champaign: Human
Kinetics, 2004.
Winter DA. Human balance and posture control during standing and walking.
Gait & Posture, 1995;3:193-214.