Journal of Biomechanics

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The influence of sagittal center of pressure offset on gait kinematics
and kinetics
Amir Haim
a,b,n
,Nimrod Rozen
c
,Alon Wolf
a
a
Biorobotics and Biomechanics Lab (BRML),Faculty of Mechanical Engineering,Technion-Israel Institute of Technology,Haifa,Israel
b
Department of Orthopedic Surgery B,Sourasky Medical Center,Tel Aviv,Israel
c
Department of Orthopaedic Surgery,Ha’Emek Medical Center,Afula,Israel
a r t i c l e i n f o
Article history:
Accepted 28 October 2009
Keywords:
Center of pressure
Coronal kinetics of the knee
Footwear-generated biomechanical
manipulations
Gait analysis
Knee flexion torque
a b s t r a c t
Objectives:Kinetic patterns of the lower extremity joints have been shown to be influenced by
modification of the location of the center of pressure (CoP) of the foot.The accepted theory is that a
shifted location of the CoP alters the distance between the ground reaction force and the center of the
joint,thereby modifying torques during gait.Various footwear designs have been reported to
significantly alter the magnitude of sagittal joint torques during gait.However,the relationship
between the CoP and the kinetic patterns in the sagittal plane has not been examined.The aim of this
study was to evaluate the association between the sagittal location of the CoP and gait patterns during
gait in healthy men.
Methods:A foot-worn biomechanical device which allows controlled manipulation of the CoP location
was utilized.Fourteen healthy men underwent successive gait analysis with the device set to convey
three different sagittal locations of the CoP:neutral,anterior offset and posterior offset.
Results:CoP translation in the sagittal plane (i.e.,from posterior to anterior) significantly related with
an ankle dorsiflexion torque and a knee extension torque shift throughout the stance phase.Likewise,
an anterior translation of the CoP significantly reduced the extension torque at the hip during pre-
swing.
Conclusions:The study results confirm a direct correlation between sagittal offset of the CoP and the
magnitude of joint torques throughout the lower extremity.
& 2009 Elsevier Ltd.All rights reserved.
1.Introduction
During the stance phase of the gait cycle,a force is applied to
the ground which is coupled with a ground reaction force (GRF).
The magnitude of the GRF is equal and its direction is opposite to
the force the body exerts (Winter,1984).Consequently,joint
torques develop which are equivalent to the magnitude of the GRF
and the perpendicular distance from the joint center to the force
(Gronley and Perry,1984;Winter,1984).Theoretically,altering
the instantaneous center of pressure (CoP) of the foot would
influence the orientation of this force and the resulting joint
torques and angles through the body segments.
This principle has been the focus of previous research which
examined the utilization of footwear-derived biomechanical
manipulation.Application of wedge insoles were found to shift
the location of the CoP in the coronal plane,thereby altering joint
torques fromthe foot proximally (Kakihana et al.,2005;Maly et al.,
2002;Xu et al.,1999) and decreasing the load at the medial
compartment of the knee joint in healthy and arthritic subjects
(Crenshaw et al.,2000;Kakihana et al.,2005;Ogata et al.,
1997;Yasuda and Sasaki,1987).In a previous study (Haim et al.,
2008),we examined the effect of controlled coronal plane CoP
modulation at the foot.The magnitude of the knee adduction
torque was found to significantly correlate with the coronal
orientation of the CoP.
Several studies have investigated the effect of sagittal plane
footwear modifications on kinematic and kinetic parameters of
the lower extremities.Walking with different heel-height shoes
has been reported to decrease stride length (de Lateur et al.,
1991),to alter joint torques in the lower extremity (Snow and
Williams,1994),and to prolong midstance knee flexor torques
during gait (Kerrigan et al.,2005).Missing-heel shoes were found
to reduce walking speed and stride length,to increase cadence,
and to considerably alter normal ankle joint function (Attinger-
Benz et al.,1998).Gait analysis of negative heel rocker sole
shoes showed an increase in cadence and a significant alteration
of proximal joint metrics (Myers et al.,2006).Similarly,
changes in CoP locus were reported with relation to rocker sole
ARTICLE IN PRESS
Contents lists available at ScienceDirect
journal homepage:www.elsevier.com/locate/jbiomech
www.JBiomech.com
Journal of Biomechanics
0021-9290/$- see front matter & 2009 Elsevier Ltd.All rights reserved.
doi:10.1016/j.jbiomech.2009.10.045
n
Corresponding author at:Biorobotics and Biomechanics Lab (BRML),Faculty of
Mechanical Engineering,Technion-Israel Institute of Technology,Haifa 32000,
Israel.Tel.:+972 52 4262129.
E-mail addresses:amirhaim@gmail.com,
alonw@tx.technion.ac.il (A.Haim).
Journal of Biomechanics 43 (2010) 969–977
ARTICLE IN PRESS
shoes (Xu et al.,1999).However,much of the above-mentioned
research utilized footwear modifications that introduced con-
siderable alterations to the normal functioning of the ankle.
The purpose of the current study was to assess the effect
of the sagittal CoP position on kinetic and kinematic parameters
of the lower extremities.Utilizing a novel foot-worn biomecha-
nical device which allows controlled manipulation of the CoP,
we hypothesized that translation of elements in the sagittal
plane (i.e.,from posterior to anterior) would result in a
matching alteration of the magnitude of lower extremity
sagittal joint torques and kinematic patterns during the stance
phase.
Table 1
Demographic data of participants (n=14).
Age (years) Height (cm) Weight (kg)
25.9572.483 177.3573.52 74.0474.12
Note:Values are mean7SD
Fig.1.Biomechanical platform and mobile elements.Notes:The biomechanical
device utilized in the study,comprising four modular elements attached onto foot-
worn platforms (APOS system,Apos—Medical and Sports Technologies Ltd.).The
device consists of two convex-shaped biomechanical elements attached to each of
the feet.Each element can be individually calibrated (Position,convexity,height
and resilience) to induce specific biomechanical challenges in multiple planes.The
elements are available in different degrees of resilience and convexity,and are
attached to the subject’s foot using a platform in the form of a shoe.
Fig.2.A.Biomechanical device at neutral sagittal configuration,B.at anterior configuration,C.at posterior configuration.In the anterior and the posterior configurations
the biomechanical elements (red spheres) are transposed anterior and posterior in relation to the neutral configuration conveying matched offset of the COP.(For
interpretation of the references to colour in this figure legend,the reader is referred to the web version of this article.)
Fig.3.Representative subject’s CoP relative offset at the posterior,neutral and
anterior configurations.The Y axis represents the vertical distance between the
instantaneous location of the CoP of the instantaneous axis heel axis (perpendi-
cular to the heel to axis crossing the heel marker.(All values are reported in mm
and negative values indicate lateral offset).The X represents 100% of stance phase
time.
Table 2
Spatio-temporal parameters,group values (n=14).
Parameters Anterior axis Neutral axis Posterior axis
Cadence (steps/min) 98.3378.21 99.3179.38 97.8178.45
Stride length (m) 1.2970.11 1.2970.12 1.3270.11
Walking speed (m/s) 1.0870.14 1.1070.17 1.170.14
Note:Mean values7standard deviation
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977970
ARTICLE IN PRESS
2.Methods
2.1.Participants
Fourteen healthy male volunteers without any known musculoskeletal or
neurologic pathology comprised the study cohort.All had the same shoe size
(French 43) and a similar anthropometric profile (i.e.,weight,height,dominant
leg).Their characteristics are noted in Table 1.
The study was approved by the Ethics Sub-Committee and all participants
gave informed consent.
2.2.The biomechanical system
A novel biomechanical device (APOS System,APOS—Medical and Sports
Technologies Ltd.Herzliya,Israel) allowing controlled manipulation of the CoP was
generously donated by the manufacturer prior to the study.A detailed description
of the device was recently reported (Haimet al.,2008).In brief,it consists of two
mobile convex-shaped biomechanical elements attached to each of the feet,
enabling flexible continuous positioning in multiple planes (Fig.1).A pilot study
conducted to assess the stability of the apparatus determined that,for healthy
adults,satisfactory walking stability can be kept within the range of 1.8 cm
posterior and 1.8 cm anterior deviation of the biomechanical elements from the
neutral position.
2.3.Experimental protocol
Prior to testing,all participants were functionally assessed by the same
physician (AH).The biomechanical device was calibrated by a qualified
physiotherapist.First positioning of the elements for the ‘‘functional neutral
configuration’’,defined as the position in which the apparatus exerted the least
valgus,varus,dorsal or plantar torque about the ankle to the individual being
examined was determined.Anterior and posterior configurations were then
defined as 1.5 cm anterior and 1.5 cm posterior deviation of the biomechanical
elements along the neutral sagittal axis (Fig.2).
Successive gait analysis testing,each with a singular calibration of the
apparatus,was performed with the biomechanical elements placed in three
conditions:neutral configuration (Fig.2a),anterior displacement (Fig.2b),
and posterior displacement (Fig.2c).To become accustomed to the testing
procedure,subjects were instructed to walk at a self-selected velocity for
several minutes which was then indicated by a metronome to ensure consistent
cadence throughout the trial.Six successful trials of each condition were collected
per subject for averaging.All conditions were tested in random order on the
same day.
2.4.Data acquisition and processing
Gait analysis of each subject was performed at the Biorobotics and Biomechanics
Lab at Technion-Israel Institute of Technology.Three-dimensional motion analysis was
performed using an 8-camera Vicon motion analysis system (Oxford Metrics Ltd.,
Oxford,UK) for kinematic data capture,at a sampling frequency of 120 Hz.The ground
reaction forces were recorded by two 3-dimensional AMTI OR6-7-1000 force plates
placed in tandemin the center of a 10-mwalkway,at a sampling frequency of 960 Hz.
Kinematic and kinetic data were collected simultaneously while the subjects walked
over the walkway.A standard marker set was used to define joint centers and axes of
rotation (Kadaba et al.,1990).Markers were attached bilaterally over the following
anatomic landmarks:the anterosuperior iliac spine,the posteriosuperior iliac spine,the
lateral midthigh,the lateral knee epicondyle,the lateral midshank,the lateral
malleolus,the head of the third metatarsal,and the posterior aspect of the heel at
the same level as the marker over the third metatarsal head.A knee alignment device
(KAD;Motion Lab Systems Inc,Baton Rouge LA) was utilized to estimate the three-
dimensional alignment of the knee flexion axis during the static trial.Sagittal plane
joint angles and torques were calculated using inverse dynamic analyses from the
kinematic data and force plates measures using ‘PlugInGait’ (Oxford Metrics,Oxford,
UK).All analyses were performed for the dominant leg.Joint moments were
normalized for body mass.
To examine the relationship between the different interventions on the
outcome measures,trial data were extracted and calculated by MATLAB
TM
software.Stride time normalized curves of the joint angles and moments were
plotted.All values were reported in association with a specific stage of the gait
cycle:initial contact (IC) 0–2%;load response (LR) 0–10%;midstance (MS) 10–30%;
terminal stance (TS) 30–50%;pre-swing (PS) 50–60%;terminal contact (TC) 60%-
Table 3
Comparison of average CoP sagittal trajectory (n=14).
Device
configuration
Anterior Neutral Posterior p
Mean Std.
Dev.
Mean Std.
Dev.
Mean Std.
Dev.
Stance phase stage
Initial contact 88.6 21.2 68.6 16.1 32.1 29.5 o0.01
Load response 84.2 17.2 53.8 6.9 24.1 16.0 o0.01
Midstance 148.4 35.7 122.9 19.3 112.8 15.1 o0.01
Terminal stance 246.6 32.4 230.2 26.2 218.9 15.9 o0.01
Pre-swing 258.1 52.7 244.0 57.6 224.8 48.0 o0.01
Terminal contact 254.5 60.7 240.8 56.5 215.1 51.8 o0.01
Note:Values represent the instantaneous CoP-heel axis vertical distance;values
reported in mm
Table 4
Comparison of the average joint kinematic parameters (mean and SD).
Anterior Neutral Posterior p
Mean Std.Dev.Mean Std.Dev.Mean Std.Dev.
Knee
Total range of motion (throughout gait cycle) 59.72 4.58 60.01 3.73 60.89 3.45 0.071
Initial contact 7.56 5.51 7.33 6.33 6.35 6.36 0.013
Peak flexion (midstance) 19.24 7.08 19.23 7.00 19.34 7.20 0.52
Peak extension (terminal stance) 7.10 5.84 6.53 5.83 5.92 6.47 0.005
Terminal contact 41.90 8.28 38.92 8.41 35.09 8.93 0.002
Peak flexion (swing phase) 63.51 7.73 63.41 7.40 64.81 8.02 0.065
Ankle
Total range of motion (throughout gait cycle) 23.73 4.41 23.19 3.51 24.34 2.90 0.395
Initial contact 3.74 3.61 3.54 3.88 2.21 4.00 0.003
Peak plantar flexion at loading response 2.82 3.83 ￿.473 4.1 ￿2.93 4 0.000
Peak dorsal flexion at midstance 19.55 5.19 19.59 4.34 19.46 4.91 0.708
Terminal contact ￿1.85 7.09 ￿0.01 7.41 2.03 6.99 0.008
Hip
Total range of motion (throughout gait cycle) 41.33 2.52 41.67 2.47 43.08 2.57 0.001
Initial contact 30.29 6.08 30.70 6.38 32.26 6.22 0.002
Peak flexion (loading response) 31.58 5.89 31.98 5.95 33.18 5.87 0.005
Peak extension (terminal stance) ￿9.75 5.01 ￿9.69 5.24 ￿9.90 4.98 0.191
Terminal contact 0.68 4.63 ￿0.62 5.19 ￿2.49 5.90 0.001
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977 971
ARTICLE IN PRESS
toe off (Perry,1992).Relative CoP offset and peak values of joints angles and
torques during different phases of the stance period were calculated and their
average was determined across six trials in each configuration for each subject.
The relative duration of the knee flexor torque at MS and extensor torque at TS
(torque duration/total gait cycle duration) was calculated as well.The individual
values of each subject were used for inter-group statistical analysis.
Calculation of the CoP trajectory with instantaneous coordinates of the CoP
recorded by the force plate and matching instantaneous coordinates of the heel
and toe markers was carried out;this method was recently described by our group
(Haimet al.,2008).Total CoP offset (i.e.,the relative distance of the CoP from the
neutral configuration) and the offset at IC,LR,MS,TS,PS and TC stance stages were
calculated.
2.5.Statistical analysis
The null hypothesis that the joint angles and moment’s magnitude were the
same for each of the walking conditions was tested each of the parameters.Non-
parametric Friedman tests were used for comparison of spatio-temporal (cadence,
step length,gait velocity),kinetic,kinematic and CoP offset parameters in the
neutral,anterior and posterior configurations of the apparatus.For the significant
results we further used Wilcoxon tests to compare each pair from the three
groups.Spearman’s correlations were used to examine the relationship of kinetic
parameters in the posterior,neutral and anterior configuration of the apparatus.A
probability of less than 0.05 was considered as statistically significant.All analyses
were performed using SPSS (version 13.0).
3.Results
3.1.Temporal–spatial variables
Cadence and walking velocity were similar for all configura-
tions of the apparatus.The stride length was 3 cm longer for the
posterior condition compared to the anterior condition;however,
this was not statistically significant (Table 2).
3.2.CoP trajectory
The CoP trajectory throughout stance shifted in accordance to
the offset of the biomechanical elements (Fig.3).Inter-subject
analysis revealed a significant relationship between CoP locus
throughout stance and the sagittal offset of the biomechanical
elements from the neutral position (Table 3).
3.2.1.Sagittal plane kinematics
There were significant differences in ankle,knee and
hip kinematics between the three test conditions (Table 4,
Fig.4a–c).
Ankle:Sagittal plane ankle total range of motion (RoM) was
similar for all conditions tested.At IC,the ankle was slightly
dorsiflexed in all conditions tested (3.741￿2.211 on average).
Anterior and posterior offset significantly related with greater and
lesser dorsal flexion,respectively,on average,1.53–6.3% of total
RoM.Immediately after IC,during LR,the ankle planter flexed.Peak
plantar flexion was significantly greater in the posterior condition
than in the anterior condition,on average,5.75–23.6% of total RoM.
During MS,the joint dorsal flexed.Peak dorsal flexion at the end of
MS was not statistically significant for the three walking conditions.
Finally,during PS,the ankle plantar flexed once more.Prior to TC,
peak plantar flexion was significantly greater in the anterior
condition than in the posterior condition,on average,3.88–15.9%
of total RoM.
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Joint angle (°)
Sagittal plane joint kinematics
Fig.4.Sagittal plane joint kinematics.(a–c):representative subject’s sagittal plane joint kinematics for the three walking conditions tested:neutral (yellow),anterior (red)
posterior (green) configurations.The Y axis represents joint angles and the X axis represents 100% of a single gait cycle.Data was sampled at the following:the intersection
of the curve with Y axis represents initial foot contact (IC).The vertical lines represent terminal foot contact (TC).a
n
—peak ankle planter flexion at loading response (LR);
a
nn
—peak ankle dorsal flexion at terminal stance (TS);a
nnn
—peak ankle planter flexion at pre-swing (PS);b
n
—peak knee flexion at midstance (MS);b
nn
—peak knee
extension at terminal-stance (TS);c
n
—peak hip flexion at loading response (LR);c
nn
—peak hip extension at pre-swing (PS).(For interpretation of the references to colour in
this figure legend,the reader is referred to the web version of this article.)
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977972
ARTICLE IN PRESS
Knee:Sagittal plane knee total RoM was similar in all
conditions tested.At IC,knee extension was on average 1.211
(5.8% of total RoM) greater for the posterior condition than for the
anterior condition.During LR phase,the knee flexed for the first
time.Peak knee flexion (during early MS) was similar for the three
walking conditions.Following this flexion peak,the knee
extended.Peak knee extension at TS was slightly greater with
the posterior shoe configuration (on average,1.18–1.96% of total
RoM) than in the anterior condition.Finally,during PS,the knee
flexed for the second time and knee flexion was on average 6.811
(11.2% of total RoM) greater at TC in the anterior condition than in
the posterior condition.Peak knee flexion occurring during the
swing phase was similar for all walking conditions.
Hip:At IC,hip flexion was on average 1.971 (4.58% of total
RoM) greater in the posterior condition than in the anterior
condition.Peak hip flexion (during the end of LR and early MS)
was on average 1.61 (3.72% of total RoM) greater in the posterior
condition than in the anterior condition.During mid and TS phase,
the hip extended.Peak hip extension (during the end of TS and
early PS) was similar in all conditions tested.At TC,the hip flexion
was on average 3.171 (7.37% of total RoM) greater in the anterior
condition than in the posterior condition.
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Knee Hip
Fig.5.Sagittal plane joint kinetics.(a–c):representative subject’s sagittal plane joint kinetics for the three walking conditions tested:neutral (yellow),anterior (red),
posterior (green).The Y axis represents joint angles and the X axis represents 100% of a single gait cycle.The intersection of the curve with Y axis represents initial foot
contact (IC).The vertical lines represent terminal foot contact (TC).a
n
—peak ankle planter flexion torque at loading response (LR);a
nn
—peak ankle dorsal flexion torque at
pre-swing (PS);b
n
—peak knee extension torque at loading response (LR);b
nn
—peak knee flexion torque at midstance (MS);b
nnn
—peak knee extension torque at terminal
stance (TS);b
nnnn
—peak knee flexion torque at pre-swing (PS);c
n
—peak hip flexion torque at loading response (LR);c
nn
—peak hip extension torque at pre-swing (PS).(For
interpretation of the references to colour in this figure legend,the reader is referred to the web version of this article.)
Table 5
Comparison of average joint kinetic parameters (mean and SD).
Anterior Neutral Posterior p
Mean Std.Dev.Mean Std.Dev.Mean Std.Dev.
Knee
Peak extension torque at loading response (N m/kg) ￿4.84 1.58 ￿4.15 1.85 ￿2.69 1.46 0.000
Peak flexion torque at midstance (Nm/kg) 6.55 3.96 7.43 4.45 8.52 4.60 0.000
Midstance flexor moment duration (% gait cycle) 27.01 5.54 28.275 4.49 31.44 4.75.202
Peak extension torque at terminal stance (N m/kg) ￿2.21 2.67 ￿1.55 2.47 ￿1.09 2.48 0.000
Terminal stance extensor moment duration (% gait cycle) 20.9 8.53 18.79 6.91 18.3 6.86.007
Peak flexion torque at pre-swing (Nm/kg) 2.26 2.28 3.05 3.33 3.44 3.19 0.000
Ankle
Initial contact (N m/kg) 0.65 0.86 0.64 0.74 0.24 0.72.004
Peak ankle planter flexion at loading response (N m/kg) ￿0.64 1.18 ￿2.29 1.19 ￿2.81 0.90 0.000
Peak ankle dorsal flexion torque at pre-swing (N m/kg) 22.04 1.76 21.44 2.31 20.99 2.20 0.223
Hip
Peak hip flexion torque at loading response (Nm/kg) 5.67 4.77 5.76 4.91 5.52 5.71 0.607
Peak hip extension at pre-swing (N m/kg) ￿12.81 4.45 ￿13.33 6.09 ￿14.09 5.54 0.001
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977 973
ARTICLE IN PRESS
3.2.2.Sagittal plane kinetics
There were significant differences in ankle,knee and hip
kinetics between the three test conditions (Table 5,Fig.5a–c,
Figs.6–8).
Ankle:A significant correlation was found between the device
configuration and the ankle torque at LR and at TS (Table 6).At IC
(Fig.5a),ankle dorsal flexion torque was lower by 0.41 Nm/kg for
the posterior configuration,as compared to the anterior
configuration,a 63% reduction (Fig.6,Table 5).Following IC,
during LR,the reaction force passes behind the joint and generates
a plantar flexion torque about the ankle.Peak plantar flexion
torque (during LR) was on average 2.17 N m/kg greater for the
posterior condition than for the anterior condition,a 77.22%
increase.During midstance and TS,the reaction force passes in
front of the joint center.The joint sagittal plane external torque is
transformed to a dorsal flexion torque.Peak dorsal flexion torque
(at the end of TS and the beginning of PS) was 1.05 N m/kg greater
in the anterior condition,a 4.76% rise.
Knee:A significant correlation was found between the device
configuration and the knee torque throughout the stance phase
(Table 6).Immediately after IC,the reaction force passes in front
of the knee (Fig.5b).On average,the peak torque was 2.15 N m/kg
greater for the anterior condition,a 44.42% rise (Fig.7,Table 5).
During MS,the line of action passes behind the knee and the
torque reverses into a flexion torque.This torque peaks early in
MS with the peak flexion angle of the knee.The peak torque was
1.97 Nm/kg lower for the anterior condition than for the
posterior condition,a 23.12% reduction.During TS,as the center
of mass passes the base of support,the reaction force once again
passes in front of the knee and the torque reverses into an
extension torque.The magnitude of the peak torque was
1.12 Nm/kg greater for the anterior condition than for the
posterior,a 50.6% change.In two subjects,the sagittal knee
torque remained flexed with the posterior configuration through-
out the entire stance period.These subjects were excluded from
the analysis of flexor/extensor torque duration.For the remaining
12 subjects extensor torque was significantly longer with the
anterior shoe configuration and the flexor torque was shorter,
although this difference was not statically significant (Table 5).
Throughout PS,the reaction force passes just behind the joint
center and induces a flexion torque;the peak torque was 1.181
less for the anterior configuration in comparison to the posterior
configuration,a 34% reduction.
Hip:A significant correlation was found between the device
configuration and the hip torque at MS (Table 6).At IC,the GRF
passes in front of the hip,bringing on a flexion sagittal torque.
This torque peaks during LR (Fig.5c).The magnitude of the torque
was similar in the three walking conditions.The torque then
diminishes and transforms into an extension torque which peaks
during PS.On average,the peak extension moment was 1.28 N m/
kg lower for the anterior configuration compared to the posterior,
a 9.08% reduction (Fig.8,Table 5).
Sagittal torque (Nm/Kg)
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Anterior Neutral Posterior
Loading response Mid stance Terminal stance Pre wing
Anterior Neutral Posterior Anterior Neutral Posterior Anterior Neutral Posterio
r
Sagittal joint angle (°)
Fig.6.Knee kinetics and kinematics during stance phase stages.Notes:relationship between group joint sagittal moment values throughout consecutive stages of gait
cycle and concomitant joint sagittal angles.Data presented as box-plots—line in center of box represents the median peak value;the box represents the interquartile range
and the whiskers represent the range.
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977974
ARTICLE IN PRESS
4.Discussion
The results presented indicate a clear association between the
magnitude of lower extremity kinetic parameters and the position
of the CoP in the sagittal plane.The present study examined the
outcome of a controlled shift of the CoP in healthy subjects.
Several footwear-generated biomechanical manipulations (e.g.,
high heels,reverse heel,rocker bottom) have been shown to
influence movement patterns in the sagittal plane.However,
these interventions introduce vigorous interference to ankle
kinematics.To the best of our knowledge,this is the first study
to utilize a biomechanical device which allows controlled
modulation of the center of pressure.
We found that anterior translation of the CoP in the sagittal
axis correlated with an ankle dorsal flexor and a knee extension
shift of the sagittal torque throughout the stance phase,a reduced
extension torque at the hip during PS and a prolonged duration of
the terminal stance knee extension torque.A reverse outcome
was found with posterior CoP translation.These findings confirm
the study’s hypothesis of a direct correlation between the sagittal
location of the CoP and the magnitude of lower extremity sagittal
joint torques.We speculate that the sagittal shifted CoP reduced
or extended the distance between the GRF and the center of the
joints throughout successive stages of the stance phase,resulting
in reduced or increased magnitude of the torques.
Kinematic patterns of the ankle,knee and hip joints were also
found to be influenced by a sagittal shift of the CoP.Sagittal
translation of the CoP from posterior to anterior offset correlated
with a flexion shift of the knee kinematic patterns and with
a bimodal pattern of the ankle and hip kinematics (ankle plantar
flexion/hip extension during initial stance and ankle dorsal flexion/
hip flexion during final stance).Kerrigan et al.(2005) examined the
effect of high-heeled shoes on gait parameters in healthy women
and reported a 20.41 increase in ankle plantar flexion throughout
the gait cycle.In the present study,the effect of anterior
and posterior CoP translation on ankle kinematics was less
profound.Preserving normal ankle function enables a controlled
setting for easement of CoP influence on kinetic parameters.
Anterior Neutral Posterior Anterior Neutral Posterior Anterior Neutral Posterior
-1
0
1
2
3
-4
-2
0
26
24
22
20
18
16
0
5
10
-5
-15
0
-5
-10
-10
0
10
20
-20
-30
5
10
Sagittal joint angle (°)
2
Initial-contact
Loading response
Pre swing
Sagittal torque (Nm/Kg)
Fig.7.Ankle kinetics and kinematics during stance phase stages.Notes:relationship between group joint sagittal moment values throughout consecutive stages of gait
cycle and concomitant joint sagittal angles.Data presented as box-plots—line in center of box represents the median peak value;the box represents the interquartile range
and the whiskers represent the range.
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977 975
ARTICLE IN PRESS
Kerrigan et al.(2005) reported greater peak knee flexion,
prolonged knee flexor torque and reduced peak knee-extensor
torque with high heels.In the present study,posterior CoP offset
correlated with similar kinetic findings (i.e.,greater and pro-
longed knee flexor torque and reduced shorter peak knee-
extensor torque).The knee sagittal torque significantly correlated
with the knee flexion angle.Interestingly,with posterior offset
configuration,knee angles were not significantly different during
midstance and were more extended during terminal stance.This
suggests that the altered kinetics recorded with the posterior
offset is a result of altered position of the GRF and is not caused by
altered joint kinematics (i.e.,increased knee flexion angles with
posterior CoP offset could have accounted for the greater flexor
torque).
Several limitations arising from the current study should be
noted.First,the relative CoP location was analyzed indirectly by
calculating instantaneous force plate recorded COP and corre-
sponding foot segment axis distance.While,this method offers a
reasonable evaluation of the COP offset and was utilized in
previous studies (Haim et al.,2008),future studies incorporating
direct COP measurement (e.g.,pedobarograph analysis) could
provide valuable data regarding shoe COP pattern modulation.
Another limitation of this study was the employment of the
apparatus at neutral position as a control.This setting was
selected to assure consistency of the kinematic model.Finally,it
should be emphasized that the participants in this study
comprised a distinctive homogenic cohort of healthy young male
adults.These results are therefore valid only for individuals with
characteristics similar to those of the tested group.Different
populations (e.g.,females who tend to have different lower
extremity joint motions compared to males due to anatomical,
muscle strengths,ligament properties) may respond differently to
such interventions.Further studies are needed before these
findings can be validated in other populations.
The results of the present study offer clinically relevant
implications to several musculoskeletal pathologies.The knee
25
15
20
-5
0
5
10
10
-
15
-
-20
25
-
-30
-35
15
30
25
20
25
30
35
40
20
15
Loading response
Pre swing
Anterior Neutral Posterior Anterior Neutral Posterio
r
35
40
5-
Sagittal torque (Nm/Kg)Sagittal joint angle (°)
Fig.8.Hip kinetics and kinematics during stance phase stages.Notes:relationship
between group joint sagittal moment values throughout consecutive stages of gait
cycle and concomitant joint sagittal angles.Data presented as box-plots—line in
center of box represents the median peak value;the box represents the
interquartile range and the whiskers represent the range.
Table 6
Spearman’s correlations analysis of kinetic parameters and device configuration.
Test variable Device configuration Anterior Neutral Posterior
Ankle moment (IC) Anterior 1;(.000)
Neutral.670;(.009) 1;(.000)
Posterior.612;(.020).504;(.066) 1;(.000)
Ankle peak plantar flexion moment (LR) Anterior 1;(.000)
Neutral.943;(.000) 1;(.000)
Posterior.701;(.005).635;(.015) 1;(.000)
Ankle peak dorsal flexion moment (PS) Anterior 1;(.000)
Neutral.824;(.000) 1;(.000)
Posterior.783;(.001).909;(.000) 1;(.000)
Knee peak extensor moment (LR) Anterior 1;(.000)
Neutral.873;(.000) 1;(.000)
Posterior.605;(.022).739;(.003) 1;(.000)
Knee peak flexor moment (MS) Anterior 1;(.000)
Neutral.974;(.000) 1;(.000)
Posterior.842;(.000).899;(.000) 1;(.000)
Knee peak extensor moment (TS) Anterior 1;(.000)
Neutral.952;(.000) 1;(.000)
Posterior.903;(.000).934;(.000) 1;(.000)
Knee peak flexor moment (PS) Anterior 1;(.000)
Neutral.912;(.000) 1;(.000)
Posterior.965;(.000).960;(.000) 1;(.000)
Hip peak flexor moment (LR) Anterior 1;(.000)
Neutral.873;(.000) 1;(.000)
Posterior.405 (.151).431 (.124) 1;(.000)
Hip peak extensor moment (MS) Anterior 1;(.000)
Neutral.982;(.000) 1;(.000)
Posterior.915;(.000).924;(.000) 1;(.000)
Values are correlation coefficients (r),P values in parentheses.
Abbreviations:IC—Initial contact;LR—Loading response;PS—pre-swing;MS—Midstance;TS—terminal stance
A.Haim et al./Journal of Biomechanics 43 (2010) 969–977976
ARTICLE IN PRESS
flexion moment during MS is proportional to the pressure across
the patellofemoral joint and has been linked with patellofemoral
pain syndrome (PFPS) and osteoarthritis (OA) of the knee
(Kerrigan et al.,1998).Similarly,it has been suggested (Astephen
et al.,2008) that interventions designed at altering knee kinetics
may be effective for halting progression of knee OA.Secondly,in
anterior curciate ligament (ACL)-deficient knees,internal moment
generated by quadriceps contraction can cause excessive anterior
tibial translation.It has been suggested that this motion can lead
to premature knee osteoarthritis.A reduction in the peak knee
flexion moment coupled by a reduced internal quadriceps
moment has been reported to be a necessary compensation to
avoid excessive anterior translation of the tibia (Andriacchi and
Dyrby,2005).Finally,patients suffering from cerebral palsy and
other neurological pathologies often experience difficulty main-
taining upright posture due to a reduction in the total support
moment (Lampe et al.,2004).Biomechanical manipulation via A
footwear design that incorporates anterior CoP offset may induce
an extension shift to the sagittal torque and provide benefit to
these patients.An extension shift to the sagittal torque could
theoretically lower patellofemoral joint pressure in knee OA
patients,diminish excessive anterior tibial translation in patients
with ACL deficient knees,and contribute to total support moment
in patients with cerebral palsy.However,such interventions
should be taken with caution;excessive extension shift to the
sagittal torque could possibly alter joint kinematics.it should be
mentioned that an extension shift to the sagittal torque may not
be safe for the knee.A reduced tendency to flex the knee can
reduce the knee joint’s capacity for shock absorption and would
likely aggravate the tibiofemoral contact stresses at the articular
cartilage.Further studies examining the benefit and safety of
moderate anterior CoP offset alterations in patients with the
above pathologies are warranted.
Conflict of interest statement
No author has any conflict of interest to declare.
Acknowledgment
The authors thank APOS—Medical and Sports Technologies
Ltd.for their generosity in contributing the devices used in the
study.
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