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Sagittal Plane Trunk Posture Influences Patellofemoral Joint Stress During Running

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Study design: Cross-sectional, repeated-measures. Objectives To examine the association between sagittal plane trunk posture and patellofemoral joint (PFJ) stress, and to determine whether modifying sagittal plane trunk posture influences PFJ stress during running. Background: Patellofemoral pain is the most common injury among runners and is thought to be the result of elevated PFJ stress. While sagittal plane trunk posture has been shown to influence tibiofemoral joint mechanics, no study has examined the influence of trunk posture on PFJ kinetics. Methods: Twenty-four asymptomatic recreational runners (12 women, 12 men) ran overground at a speed of 3.4 m/s under 3 trunk-posture conditions: self-selected, flexed, and extended. Trunk and knee kinematics, ground reaction forces, and electromyographic signals from selected lower extremity muscles were obtained. A previously described PFJ biomechanical model was used to quantify PFJ stress. Results: The mean ± SD trunk flexion angles under the self-selected, flexed, and extended running conditions were 7.3° ± 3.6°, 14.1° ± 4.8°, and 4.0° ± 3.9°, respectively. A significant inverse relationship was observed between mean trunk flexion angle and peak PFJ stress during the self-selected condition (r = -0.60, P = .002). Peak PFJ stress was significantly lower in the flexed condition (mean ± SD, 20.2 ± 3.4 MPa; P<.001) and significantly higher in the extended condition (23.1 ± 3.4 MPa; P<.001) compared to the self-selected condition (21.5 ± 3.2 MPa). Conclusion: Sagittal plane trunk posture has a significant influence on PFJ kinetics during running. Incorporation of a forward trunk lean may be an effective strategy to reduce PFJ stress during running.
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journal of orthopaedic & sports physical therapy | volume 44 | number 10 | october 2014 | 785
[ research report ]
Running is a popular form of exercise, with approximately 36
million people engaging in this activity in the United States
alone.36 Despite the positive health eects associated with
running, a high incidence of lower extremity running injuries
has been reported (19%-79%).21,40,43,44 Among these injuries, half
occur at the knee joint, with patellofemo-
ral pain (PFP) being the most common
diagnosis.40,43
It has been proposed that PFP is the
result of elevated patellofemoral joint
(PFJ) stress.10,16 As stress is defined as
force per unit area, elevated PFJ stress
could occur as a result of an increase in
the PFJ reaction force and/or a decrease
in contact area between the patella and
the trochlear groove of the femur. In turn,
an increase in the PFJ reaction force
would occur with an increase in the knee
extensor moment and/or knee flexion
angle.4,16,23 Additionally, PFJ contact area
increases with knee flexion and decreases
with knee extension.32,37
To reduce risk of PFP in runners,
modification of the foot strike pattern
has been proposed. Specifically, convert-
ing from a rearfoot to a forefoot or mid-
foot strike pattern has been promoted as
a means to reduce the peak impact force,
loading rate, and knee extensor mo-
ment.5,8,12,18,19,38 In a case series, Cheung
and Davis12 reported that individuals with
PFP exhibited improvements in pain af-
ter transitioning to a nonrearfoot strike
pattern. Furthermore, barefoot running,
which typically results in a forefoot or
midfoot strike pattern,5,25,46 has been re-
ported to decrease peak PFJ stress by 12%
in asymptomatic runners.6 Although cur-
rent literature supports the use of modi-
fying foot strike pattern to reduce PFJ
loading, several studies have reported
that adopting a forefoot and/or midfoot
strike pattern leads to increased loading
STUDY DESIGN: Cross-sectional, repeated-
measures.
OBJECTIVES: To examine the association
between sagittal plane trunk posture and patel-
lofemoral joint (PFJ) stress, and to determine
whether modifying sagittal plane trunk posture
influences PFJ stress during running.
BACKGROUND: Patellofemoral pain is the most
common injury among runners and is thought to
be the result of elevated PFJ stress. While sagittal
plane trunk posture has been shown to influence
tibiofemoral joint mechanics, no study has exam-
ined the influence of trunk posture on PFJ kinetics.
METHODS: Twenty-four asymptomatic
recreational runners (12 women, 12 men) ran
overground at a speed of 3.4 m/s under 3 trunk-
posture conditions: self-selected, flexed, and
extended. Trunk and knee kinematics, ground reac-
tion forces, and electromyographic signals from
selected lower extremity muscles were obtained. A
previously described PFJ biomechanical model was
used to quantify PFJ stress.
RESULTS: The mean SD trunk flexion angles
under the self-selected, flexed, and extended
running conditions were 7. 3.6°, 14.1° 4.8°,
and 4.0° 3.9°, respectively. A significant inverse
relationship was observed between mean trunk
flexion angle and peak PFJ stress during the self-
selected condition (r = –0.60, P = .002). Peak PFJ
stress was significantly lower in the flexed condi-
tion (mean SD, 20.2 3.4 MPa; P<.001) and
significantly higher in the extended condition (23.1
3.4 MPa; P<.001) compared to the self-selected
condition (21.5 3.2 MPa).
CONCLUSION: Sagittal plane trunk posture
has a significant influence on PFJ kinetics dur-
ing running. Incorporation of a forward trunk
lean may be an eective strategy to reduce PFJ
stress during running. J Orthop Sports Phys
Ther 2014;44(10):785-792. Epub 25 August 2014.
doi:10.2519/jospt.2014.5249
KEY WORDS: anterior knee pain,
chondromalacia, patella
1Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA. 2Department of Radiology and Biomedical Imaging, University of California
San Francisco, San Francisco, CA. This study was approved by the Health Science Institutional Review Board of the University of Southern California. This study was partially
funded by the International Society of Biomechanics Dissertation Grant. The authors certify that they have no aliations with or financial involvement in any organization or
entity with a direct financial interest in the subject matter or materials discussed in the article. Address correspondence to Dr Hsiang-Ling Teng, University of California San
Francisco, Department of Radiology and Biomedical Imaging, 185 Berry Street, Suite 350, San Francisco, CA 94107. E-mail: Hsiang-Ling.Teng@ucsf.edu Copyright ©2014
Journal of Orthopaedic & Sports Physical Therapy®
HSIANG-LING TENG, PT, PhD1,2 • CHRISTOPHER M. POWERS, PT, PhD1
Sagittal Plane Trunk Posture
Influences Patellofemoral Joint
Stress During Running
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at the ankle plantar flexors.2,5,8,19,31,35,46
Recent studies suggest that sagittal
plane trunk posture may be associated
with tibiofemoral joint biomechanics
during weight-bearing activities. For ex-
ample, a forward trunk lean posture has
been found to be associated with lower
knee extensor moments during walking,
stair ascent, and single-leg-hop land-
ing.3,24,30 Based on these findings, modi-
fying sagittal plane trunk posture may
provide an alternative means to reduce
PFJ stress during running.
Using a previously described biome-
chanical PFJ model,9,10,13,20 the purpose
of the current study was 3-fold. First, we
sought to examine the association be-
tween sagittal plane trunk posture and
PFJ stress using a self-selected trunk
posture. Second, we evaluated the eects
of modifying sagittal plane trunk posture
on PFJ stress during running. A tertia-
ry purpose of this study was to identify
patellofemoral and tibiofemoral kine-
matics and kinetics that may explain the
changes in PFJ stress while running with
dierent trunk postures. Based on exist-
ing literature evaluating the influence of
trunk posture on tibiofemoral joint kinet-
ics and kinematics, we hypothesized that
an individual’s self-selected trunk flexion
angle would be inversely associated with
the peak PFJ stress during the stance
phase of running. We also hypothesized
that, compared to a self-selected trunk
posture, a more flexed trunk posture
would result in a decrease in peak PFJ
stress during running and, conversely,
a more extended trunk posture would
result in an increase in peak PFJ stress.
Understanding the association between
sagittal plane trunk posture and PFJ
stress during running may advance the
understanding of the etiology of PFP in
runners and facilitate the development of
running techniques to reduce PFJ load-
ing in this population.
METHODS
Participants
Twenty-four recreational run-
ners between the ages of 18 and 39
years participated in this study (12
men, 12 women) (TABLE 1). Participants
were natural rearfoot strikers, which was
verified using sagittal plane images from
high-speed video (sampling rate, 125 Hz).
Potential participants were excluded if
they reported any of the following: (1)
current lower extremity or low back pain,
(2) previous history of lower extremity or
low back surgery, and (3) lower extremity
or low back pathology that caused pain
or discomfort during running within 6
months prior to participation.
Instrumentation
Three-dimensional trunk and lower ex-
tremity kinematics were collected using
an 11-camera motion-capture system
(Qualisys AB, Göteborg, Sweden) at a
sampling rate of 250 Hz. Ground reac-
tion forces were obtained at a rate of 1500
Hz using a single force plate (Advanced
Mechanical Technology, Inc, Watertown,
MA). Electromyographic (EMG) signals
of selected lower extremity muscles were
collected at a sampling rate of 1500 Hz
using a wireless EMG system (Telemyo
DTS; Noraxon USA Inc, Scottsdale,
AZ) and Ag/AgCl surface electrodes
(Norotrode 20; Myotronics-Noromed,
Inc, Kent, WA). The EMG system had a
dierential input impedance of greater
than 100 MΩ, a common-mode rejection
ratio greater than 100 dB, and a baseline
noise of less than 1 µV root-mean-square.
Marker, ground reaction force, and EMG
data were collected and synchronized us-
ing motion-capture software (Track Man-
ager Version 2.8; Qualisys AB).
Procedures
Data were collected at the Jacquelin Perry
Musculoskeletal Biomechanics Research
Laboratory at the University of Southern
California. Prior to participation, partici-
pants were informed as to the objectives,
procedures, and potential risks of par-
ticipation in the study and provided in-
formed consent as approved by the Health
Science Institutional Review Board of the
University of Southern California.
Participants wore shorts, tank tops,
and their personal running shoes during
the evaluation. Data were obtained from
each participant’s dominant leg. Leg
dominance was determined by asking the
participants which leg they preferred to
use when kicking a ball.
Participants were first instrument-
ed with EMG electrodes. Electromyo-
graphic signals were recorded from the
knee flexor muscles (medial and lateral
hamstrings and gastrocnemius), and data
were used to account for muscle cocon-
traction in our biomechanical model.
The electrodes of the medial and lateral
hamstrings were placed midway between
the ischial tuberosity and the medial and
lateral sides of the popliteal fossa, respec-
tively.34 The electrodes for the medial
and lateral gastrocnemius were placed
at one third of the distance between the
medial and lateral sides of the popliteal
fossa, respectively, and the Achilles ten-
don insertion, starting from the popliteal
fossa.34 Prior to placement of the EMG
electrodes, the skin was shaved, abraded,
and cleaned with isopropyl alcohol to re-
duce electrical impedance.
Following electrode placement, partic-
ipants were asked to warm up by jogging
TABLE 1 Participant Demographics*
*Values are mean SD.
Men (n = 12) Women (n = 12)
Age, y 28.1 7.2 26.5 6.4
Height, m 1.74 0.08 1.66 0.08
Weight, kg 70.5 7. 0 62.7 6.6
Running distance, km/wk 19.3 10.1 22.9 11.1
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at a self-selected speed on a treadmill
for 5 minutes. After the warm-up, EMG
signals were collected during a maximal
voluntary isometric contraction (MVIC).
The MVIC test for the medial and lateral
hamstrings was performed with partici-
pants in a seated position, with their hip
and knee joints at 85° and 60° of flexion,
respectively.1 A strap was secured around
the distal tibia just superior to the lat-
eral malleolus to resist knee flexion. The
MVIC test for the medial and lateral
gastrocnemius was performed in stand-
ing. Participants stood on the tested leg
and raised their heel against resistance,
which was applied by a fixed bar across
the shoulders. The ankle of the tested
leg was at 15° of plantar flexion, and the
knee was fully extended during testing.1
During each MVIC test, participants
were instructed to produce a maximum
eort. Three trials of a 5-second MVIC
were obtained from each muscle, with a
40-second break between trials.7,3 9
Prior to the running trials, 21 anatom-
ical markers (reflective 14-mm diameter)
were placed on the following bony land-
marks: end of second toes, first and fifth
metatarsal heads, medial and lateral mal-
leoli, medial and lateral epicondyles of
femurs, greater trochanters, iliac crests,
L5-S1 junction, and acromioclavicular
joints. In addition, tracking marker clus-
ters mounted on semi-rigid plastic plates
were placed on the lateral surfaces of the
participant’s thighs, shanks, and heel
counters of the shoes. A standing calibra-
tion trial was first obtained to define the
segmental coordinate systems and joint
axes. After the calibration trial, anatomi-
cal markers were removed, except for
those at the iliac crests, L5-S1 junction,
and acromioclavicular joints. The track-
ing markers remained on the participant
throughout the entire data-collection
session.
Participants were instructed to run
at a controlled speed of 3.4 m/s along a
14-m runway using 3 dierent trunk pos-
tures: self-selected, flexed, and extended
(FIGURE 1). Participants first ran using
their self-selected trunk posture. During
the flexed condition, participants were
instructed to increase their trunk flexion
angle within a range in which they felt
comfortable when running. Similarly,
participants were asked to decrease their
trunk flexion angle during the extended
condition.
The order of the flexed and extended
conditions was randomized for each par-
ticipant. Practice trials were permitted
to allow participants to become familiar
with the running speed and various trunk
postures. Five successful running trials
were obtained for each trunk condition.
A trial was counted as successful when
the foot of the dominant leg fell within
the borders of the force plate from initial
contact to toe-o and the running speed
was within 5% of the target velocity.
Data Analysis
Kinematic and kinetic data were pro-
cessed and analyzed using Visual3D
software (C-Motion, Inc, Germantown,
MD). Marker trajectory data were low-
pass filtered at 12 Hz, using a fourth-or-
der Butterworth filter. The trunk segment
was defined by markers placed bilaterally
on the iliac crests and acromioclavicular
joints.29 The pelvis and trunk segments
were modeled as cylinders, and the lower
extremity segments were modeled as
frusta of cones. The local orthogonal
coordinate systems of the trunk, pelvis,
thigh, shank, and foot segments were de-
rived from the standing calibration trial.
Joint kinematics were calculated using a
Cardan rotation sequence in an order of
flexion/extension, abduction/adduction,
and internal/external rotation. The trunk
angle was calculated as the orientation of
the trunk segment relative to the global
coordinate system (global vertical axis).
Knee kinematics were calculated as the
motion of the shank relative to the thigh.
The net knee joint moment was com-
puted using inverse-dynamics equations.
Moment data were expressed as internal
(muscle) moments and normalized to
each participant’s body mass.
Electromyographic data were pro-
cessed using MATLAB software (The
MathWorks, Inc, Natick, MA). Raw EMG
signals were band-pass filtered (20-450
Hz, fourth-order Butterworth),15,28 recti-
fied, and smoothed using a 10-Hz low-
pass filter (fourth-order Butterworth).11
The smoothed EMG data during the
stance phase of running were normalized
to the average EMG intensity recorded
from the middle 3 seconds of the MVIC
trials. The stance phase was defined when
the vertical ground reaction force exceed-
ed 30 N.
FIGURE 1. Trunk posture and lower extremity biomechanics were obtained during 3 trunk conditions: (A) extended,
(B) self-selected, and (C) flexed.
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[ research report ]
A previously described sagittal plane
biomechanical model was used to quan-
tify PFJ reaction force and stress (FIGURE
2).9,10,13,20 Input variables for the model al-
gorithm consisted of participant-specific
kinematics and kinetics (ie, knee flexion
angle and adjusted knee extensor mo-
ment) and data from previous literature
(ie, PFJ contact area,32 quadriceps ef-
fective lever arm,41 and relationship be-
tween quadriceps force and PFJ reaction
force42).
To account for cocontraction at the
knee joint during running, an estimation
of knee flexor moment was required. The
knee flexor moment was calculated us-
ing SIMM modeling software (Motion
Analysis Corporation, Santa Rosa, CA).
Using SIMM, a generic lower extremity
musculoskeletal model was created with
6 musculotendon actuators: semitendi-
nosus, semimembranosus, biceps femoris
long and short heads, and medial and lat-
eral gastrocnemius.14 The SIMM model
also contained information about peak
isometric muscle force, optimal muscle
fiber length, pennation angle, and tendon
slack length.14,17,27,45
The input variables of the SIMM
model were participant-specific lower
extremity kinematics and normalized
EMG of the knee flexors. Lower extrem-
ity kinematic data were used to deter-
mine individual muscle tendon lengths
and contraction velocities for the Hill-
type muscle model in SIMM. Normalized
EMG data were used to represent the lev-
el of muscle activation. Muscle activation
of the semitendinosus was assumed to be
the same as that of the semimembra-
nosus, and the biceps femoris long and
short heads were assumed to have the
same activation.26 Torque produced by
each knee flexor muscle was computed,
added together, and normalized to body
weight to represent knee flexor moment.
To obtain a more accurate assessment of
the knee extensor moment during run-
ning, the knee flexor moment calculated
by the SIMM model was added to the net
knee extensor moment, as quantified us-
ing the inverse-dynamics equations. This
resulted in an adjusted knee extensor
moment that accounted for antagonist
muscle activation.
The first step of the model algorithm
was to approximate the quadriceps force.
First, the eective lever arm of the quad-
riceps was determined at each degree of
knee flexion by fitting a nonlinear equa-
tion to the data of van Eijden et al.41 Next,
the quadriceps force was calculated by
dividing the adjusted knee extensor mo-
ment calculated during running by the
eective lever arm.
The second step of the algorithm was
to estimate the PFJ reaction force. This
was accomplished by multiplying the
quadriceps force by a ratio reported by
van Eijden et al,42 which defined the re-
lationship between quadriceps force and
PFJ reaction force as a function of knee
flexion angle. The third step of the algo-
rithm was to calculate PFJ stress. The
PFJ reaction force obtained in the second
step was divided by the PFJ contact area,
which was determined using a second-
order polynomial curve fitted to data of
Powers et al.32 The model outputs were
PFJ stress and reaction force as a func-
tion of the gait cycle.
The primary variables of interest
were the mean trunk flexion angle and
peak PFJ stress during the stance phase
of running. The secondary variables of
interest included PFJ reaction force, PFJ
contact area, adjusted knee extensor mo-
ment, and knee flexion angle. Each of
these variables was analyzed at the time
of peak PFJ stress. All variables were
calculated for each stride and averaged
over 5 successful strides for each trunk
condition.
Statistical Analysis
A Pearson product-moment correla-
tion was used to examine the associa-
tion between mean sagittal plane trunk
posture and peak PFJ stress during the
self-selected condition. Separate repeat-
ed-measures, 1-way analyses of variance
(ANOVAs) were used to assess dier-
ences in each variable of interest among
the 3 trunk conditions. For all significant
ANOVA tests, post hoc Bonferroni tests
were employed. All statistical analyses
were performed using PASW Statistics
software (SPSS Inc, Chicago, IL). The
level of statistical significance was set at
.05.
RESULTS
Self-Selected Trunk Posture
and PFJ Stress
Results of Pearson correlation
indicated a significant inverse cor-
relation between mean trunk flexion
Net knee joint moment Knee flexor moment
Quadriceps eective
lever arm
Relationship between
QF and PFJ RF
PFJ stress
Adjusted knee
extensor moment
PFJ RF
Knee flexion angle
QF
PFJ contact area*
FIGURE 2. Flow chart of patellofemoral joint model. *Data from Powers et al.32 Data from van Eijden et al.41 Data
from van Eijden et al.42 Abbreviations: PFJ, patellofemoral joint; QF, quadriceps forcce; RF, reaction force.
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journal of orthopaedic & sports physical therapy | volume 44 | number 10 | october 2014 | 789
angle and peak PFJ stress for the self-
selected condition (r = –0.60, P = .002)
(FIGURE 3).
Trunk Kinematics
Sagittal plane trunk posture during the
stance phase of running for the 3 trunk
conditions is presented in FIGURE 4. The
ANOVA comparing average trunk flex-
ion angle across the 3 trunk conditions
indicated a significant dierence across
conditions (P<.001). Post hoc analysis re-
vealed that, compared to the self-selected
condition (mean SD, 7.3° 3.6°), there
was a significant increase in mean trunk
flexion angle during the flexed condition
(14.1° 4.8°, P<.001) and a significant
decrease in mean trunk flexion angle dur-
ing the extended condition (4.0° 3.9°,
P<.001).
PFJ Biomechanics
Patellofemoral joint stress during the
stance phase of running for the 3 trunk
conditions is presented in FIGURE 5. The
ANOVA comparing peak PFJ stress
across the 3 trunk conditions indicated
a significant dierence across conditions
(P<.001) (TABLE 2). Post hoc analysis re-
vealed that peak PFJ stress was signifi-
cantly lower during the flexed condition
(mean SD, 20.2 3.4 MPa; P<.001)
and significantly higher during the ex-
tended condition (23.1 3.4 MPa,
P<.001) when compared to the self-se-
lected condition (21.5 3.2 MPa).
The ANOVA comparing PFJ reaction
force at the time of peak PFJ stress across
the 3 trunk conditions also indicated a
significant dierence across conditions
(P<.001) (TABLE 2). Post hoc analysis re-
vealed that the PFJ reaction force at the
time of peak stress was significantly lower
during the flexed condition (mean SD,
71.0 11.1 N/kg; P<.001) and signifi-
cantly higher during the extended con-
dition (81.3 12.7 N/kg, P<.001) when
compared to the self-selected condition
(75.0 10.2 N/kg).
The ANOVA comparing PFJ contact
area at the time of peak stress across the
3 trunk conditions indicated a significant
dierence across conditions (P = .001)
(TABLE 2). Post hoc analysis revealed that
the PFJ contact area at the time of peak
stress was significantly larger during the
flexed (mean SD, 232.5 4.2 mm2; P
= .048) and extended (233.5 4.5 mm2,
P = .001) conditions when compared to
the self-selected condition (231.6 4.4
mm2).
Tibiofemoral Joint Biomechanics
The ANOVA comparing adjusted knee
extensor moment at the time of peak PFJ
stress across the 3 trunk conditions was
significant (P<.001) (TABLE 2). Post hoc
analysis revealed that the adjusted knee
extensor moment at the time of peak
stress was significantly lower during the
flexed condition (mean SD, 3.29
0.34 Nm/kg; P<.001) and significantly
higher during the extended condition
(3.70 0.32 Nm/kg, P<.001) when com-
pared to the self-selected condition (3.54
0.31 Nm/kg).
The ANOVA comparing knee flexion
angle at the time of peak stress across
the 3 trunk conditions also was signifi-
cant (P<.001) (TABLE 2). Post hoc analysis
revealed that the knee flexion angle at
the time of peak stress was significantly
higher during the flexed (mean SD,
44.5° 3.7°; P = .046) and extended
(45.5° 4.6°, P = .001) conditions when
compared to the self-selected condition
(43.6° 3.5°).
DISCUSSION
The findings of the current
study support the hypothesis that
an individual’s self-selected sagit-
tal plane trunk posture is associated with
peak PFJ stress during running. Specifi-
cally, individuals who ran with a more
flexed trunk posture exhibited lower peak
PFJ stress. In contrast, individuals who
ran with a more upright trunk posture
exhibited higher peak PFJ stress. Fur-
thermore, our findings support the prem-
0
0246810121416
5
10
15
20
25
30
35
Mean Trunk Flexion Angle, deg
Peak PFJ Stress, MPa
r = –0.60
P = .002
Women Men
FIGURE 3. Association between peak PFJ stress
and mean trunk flexion angle during the self-
selected trunk-posture condition. Abbreviation: PFJ,
patellofemoral joint.
0
0102040
30 50 7060 80 90 100
2
6
4
8
10
12
14
16
18
Stance Phase, %
Trunk Flexion Angle, deg
Flexed ExtendedSelf-selected
FIGURE 4. Sagittal plane trunk posture during the
stance phase of running under 3 trunk conditions:
extended, flexed, and self-selected. The shaded area
represents 1 SD for the self-selected condition.
0
0102040
30 50 7060 80 90 100
5
10
15
20
25
Stance Phase, %
PFJ Stress, MPa
Flexed ExtendedSelf-selected
FIGURE 5. Patellofemoral joint stress during the
stance phase of running under 3 trunk conditions:
extended, flexed, and self-selected. The shaded area
represents 1 SD for the self-selected condition.
Abbreviation: PFJ, patellofemoral joint.
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790 | october 2014 | volume 44 | number 10 | journal of orthopaedic & sports physical therapy
[ research report ]
ise that modifying sagittal plane trunk
posture can result in significant changes
in PFJ stress during running. On average,
a 6.8° increase in the mean trunk flexion
angle resulted in a 6.0% decrease in peak
PFJ stress, whereas a 3.3° decrease in
mean trunk flexion angle led to a 7.4%
increase in peak PFJ stress.
The changes in PFJ stress during the
dierent trunk postures were primarily
driven by changes in PFJ reaction force
as opposed to PFJ contact area. When
compared to the self-selected condi-
tion, the PFJ reaction force at the time of
peak PFJ stress decreased by 5.3% in the
flexed condition and increased by 8.4%
in the extended condition. Conversely,
the changes in PFJ contact area across
the dierent trunk conditions were less
than 1%. In contrast to findings by Len-
hart et al,23 who reported that a change
in knee flexion was the most important
predictor of PFJ loading during run-
ning, the observed changes in PFJ reac-
tion force in the current study appeared
to be influenced to a greater extent by
the adjusted knee extensor moment as
opposed to the knee flexion angle. This
was reflected by the fact that adjusted
knee extensor moment at the time of
peak PFJ stress decreased by 7.1% in the
flexed condition and increased by 4.5% in
the extended condition. In contrast, the
changes in knee flexion angle were less
than 2° across all conditions.
The finding that an increase in the
forward trunk lean resulted in a decrease
in the knee extensor moment is in agree-
ment with previous studies.3,24,30 Asay et
al3 reported that a 6.3° increase in the
trunk flexion angle was associated with a
35.2% lower peak knee extensor moment
during stair ascent. In addition, Ober-
länder et al30 reported that a 6° greater
forward trunk lean resulted in a 15% re-
duction in peak knee extensor moment
during hop landing.
The results of the current study have
several clinical implications. First, the
observed inverse correlation between
trunk flexion angle and PFJ stress (r
= –0.60) suggests that running with a
relatively extended trunk posture may
be a contributing factor with respect to
the development of PFP. However, lon-
gitudinal studies are needed to verify
this hypothesis. Second, incorporating a
forward-lean trunk posture during run-
ning could be used as a strategy to reduce
PFJ loading in runners. For example, our
data suggest that increasing one’s natural
trunk flexion angle by approximately 7°
could lead to a 6.0% reduction in peak
PFJ stress (1.3 MPa). Although the eects
of increased trunk forward lean on PFP
symptoms were not examined in the cur-
rent study, Powers et al33 reported that a
1-MPa decrease in PFJ stress during fast
walking corresponded to a 56% decrease
in pain in individuals with PFP. Given the
repetitive nature of running, a small re-
duction in PFJ stress per step could result
in meaningful reductions in cumulative
PFJ loading. Further studies are needed
to examine the ecacy of forward trunk
lean on PFP in symptomatic runners who
presented with a more upright trunk
posture.
Recent studies have advocated chang-
ing the foot strike pattern and/or in-
creasing step rate to reduce PFJ loading.
Kulmala et al22 reported that a forefoot
strike pattern resulted in a 14.6% reduc-
tion in peak PFJ stress compared to a
rearfoot strike pattern. Bonacci et al6 re-
ported that barefoot running led to a 12%
reduction in peak PFJ stress compared to
shod running. In addition, Lenhart et al23
found that increasing step rate by 10%
resulted in a 14% decrease in peak PFJ
reaction force.
The findings of the current study sug-
gest that incorporating a forward-lean
trunk can be used as an alternative strat-
egy to reduce PFJ loading as opposed
to the aforementioned running modifi-
cations. For example, a 10° increase in
sagittal plane trunk flexion was found to
lead to a similar percent of reduction in
PFJ loading (13.4% decrease in peak PFJ
stress and 13.8% decrease in PFJ reaction
force) without changing the foot strike
pattern. This is important, as barefoot
running as well as adopting a forefoot or
midfoot strike pattern has been shown
to increase the mechanical demand of
the ankle plantar flexors.2,5,8,19,31,35,46 Fur-
thermore, post hoc analysis revealed that
there was no significant dierence in
ankle plantar flexor moment at the time
of peak PFJ stress across the 3 trunk
conditions. We propose that adopting a
forward-lean trunk posture during run-
ning may be a preferable strategy to re-
duce PFJ stress without increasing the
mechanical demand on ankle plantar
flexors.
The change in trunk flexion angle in
the flexed condition was achieved, at least
in part, by an increase in hip flexion. Post
hoc analysis revealed a small but signifi-
cant increase in hip flexion angle at the
TABLE 2
Comparison of Patellofemoral
and Tibiofemoral Joint Biomechanics
at the Time of Peak Patellofemoral Joint
Stress During Flexed, Self-Selected,
and Extended Trunk Conditions*
Abbreviation: PFJ, patellofemoral joint.
*Values are mean SD.
Significantly dierent from self-selected trunk condition (P<.05).
Flexed Self-Selected Extended
PFJ stress, MPa 20.2 3.421.5 3.2 23.1 3.4
PFJ reaction force, N/kg 71.0 11.175.0 10.2 81.3 12.7
PFJ contact area, mm2232.5 4.2231.6 4.4 233.5 4.5
Adjusted knee extensor moment, Nm/kg 3.29 0.343.54 0.31 3.70 0.3 2
Knee flexion angle, deg 44.5 3.743.6 3.5 45.5 4.6
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time of peak PFJ stress in the flexed con-
dition (mean SD, 33.5° 7.0°; P<.001)
compared to the self-selected condition
(29.9° 5.9°). No significant dier-
ence in hip flexion angle was observed
between the extended (29.6° 6.5°, P =
1.0) and self-selected conditions. As such,
it is reasonable to assume that utilization
of a forward trunk lean during running
may result in an increased demand on the
hip extensors.
Several limitations need to be con-
sidered when interpreting the results of
this study. First, a planar (2-dimensional)
model was used to estimate PFJ stress. As
such, our approach did not account for
joint motions and forces in the frontal
and transverse planes. However, previ-
ous studies using this modeling approach
have been able to discriminate between
individuals with and without PFP.10 Sec-
ond, only healthy individuals were ex-
amined in this study. Caution should be
taken when generalizing the results to
various patient populations. Third, we
did not obtain running performance or
comfort data as part of the study. It is un-
clear how altering trunk posture would
aect oxygen consumption or comfort
levels during bouts of prolonged running.
CONCLUSION
An individual’s self-selected
sagittal plane trunk posture was
inversely associated with PFJ stress
during running. Specifically, an upright
trunk posture was found to be associated
with higher peak PFJ stress. In addition,
a 6.8° increase in sagittal plane trunk
flexion resulted in a significant reduction
in PFJ stress. The change in PFJ stress
primarily was due to changes in the PFJ
reaction force, which was driven by a
reduction in the adjusted knee exten-
sor moment. Based on our findings, we
propose that an upright trunk posture
during running may predispose an indi-
vidual to a higher risk of PFP. In addition,
incorporating a forward-lean trunk dur-
ing running may be an alternative means
to reduce PFJ stress, as opposed to run-
ning modifications such as changing foot
strike pattern, barefoot running, and in-
creasing step rate. t
KEY POINTS
FINDINGS: A more upright trunk posture
during running was found to be as-
sociated with higher peak PFJ stress. A
relatively small increase in sagittal plane
trunk flexion posture led to significant
reduction in peak PFJ stress.
IMPLICATIONS: An upright trunk posture
during running may expose an individu-
al to a higher risk of PFP. Incorporating
a slightly forward-leaning trunk posture
during running may be an alternative
means to reducing PFJ stress.
CAUTION: Only healthy individuals were
examined in this study. Caution should
be taken when generalizing the results
to various patient populations.
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... The recent literature has highlighted the important role of sagittal plane trunk posture on PFJ stress during running in runners with PFP 4) . Specifically, in healthy runners, running with an upright trunk posture is associated with elevated PFJ stress and reaction forces due to an increased knee extensor moment 3,5) . The increases in knee extensor moment are mainly driven by an increased knee lever arm (perpendicular distance from the axis of the knee joint to the ground reaction force vector) as a result of a posterior shift of vertical ground reaction force from decreased trunk flexion 3) . ...
... The sagittal plane kinematics and kinetics of the trunk and lower extremities were computed using Visual 3D software (C-Motion, Germantown, MD, USA). The trunk segment was defined by markers placed bilaterally on iliac crests and acromioclavicular joints 3,5) . The trunk and pelvis were modeled as a cylinder, and the lower extremity segments were modeled as a cone 3,5) . ...
... The trunk segment was defined by markers placed bilaterally on iliac crests and acromioclavicular joints 3,5) . The trunk and pelvis were modeled as a cylinder, and the lower extremity segments were modeled as a cone 3,5) . The trunk flexion angle was calculated as the orientation of the trunk segment relative to the global coordinate system of the laboratory 3,5) . ...
Article
[Purpose] To determine if runners with patellofemoral pain (PFP) exhibit higher patellofemoral joint (PFJ) stress and trunk extension compared to pain-free runners during treadmill running. [Participants and Methods] Twelve runners (7 with PFP and 5 pain-free) participated in this study. Participants ran at 3 different running conditions: self-selected, fast (120% of self-selected), and slow (80% of self-selected) speeds. Kinematics and kinetics of trunk and lower extremities were obtained. PFJ stress, PFJ reaction force, and PFJ contact area were determined using a biomechanical model. Two-factor ANOVAs with repeated measures were used to compare outcome variables between 3 speeds and between 2 groups. [Results] There was no significant difference in peak PFJ stress between groups across the 3 speeds. Peak PFJ stress was lowest during slow running compared to fast and self-selected running speed conditions across both groups. No significant difference was found in trunk flexion angle, PFJ reaction force, or PFJ contact area between groups across the 3 speeds. [Conclusion] Runners with and without PFP exhibited similar peak PFJ stress and trunk flexion angle during treadmill running. This preliminary work does not support the theory that reduced trunk flexion during running contributes to increased PFJ stress in runners with PFP.
... Increasing the running step rate diminishes the negative work performed at the hip and knee joints (14) or decreasing the step length can decrease PFJ stress (42,43). Similarly, postural modifications such as forward trunk-leaning seem effective in reducing PFJ stress (10,32,33), because trunk orientation during walking (18) or running (1,2,32,33) also significantly redistributes the mechanical demands of lower-limb joints. This is mainly because of changing the orientation (3) and position (28) of the ground reaction force vector relative to the lower-limb joints. ...
... Forward trunk-leaning has already been shown to mitigate PFJ stress during running on even (32,33) or sloped (15) surfaces. During even running (32,33), the reduction of PFJ stress because of forward trunk-leaning occurs without placing further mechanical stress on ankle plantar-flexors (32)(33)(34). ...
... Forward trunk-leaning has already been shown to mitigate PFJ stress during running on even (32,33) or sloped (15) surfaces. During even running (32,33), the reduction of PFJ stress because of forward trunk-leaning occurs without placing further mechanical stress on ankle plantar-flexors (32)(33)(34). This strategy differs to changing foot-strike pattern and step-rate in so much that the latter modifications shift biomechanical loading more distally (10,19,27), which may be associated with higher risks of ankle and foot injuries. ...
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Although decline surfaces or a more upright trunk posture during running increase the patellofemoral joint (PFJ) contact force and stress, less is known about these kinetic parameters under simultaneous changes to the running posture and surface height. This study aimed to investigate the interaction between Step (10-cm drop-step and level step) and Posture (trunk angle from the vertical: self-selected, ∼15°; backward, ∼0°; forward, ∼25°) on PFJ kinetics (primary outcomes) and knee kinematics and kinetics as well as hip and ankle kinetics (secondary outcomes) in 12 runners at 3.5 ms-1. Two-way repeated measures analyses of variance (α = 0.05) revealed no step-related changes in peak PFJ kinetics across running postures; however, a decreased peak knee flexion angle and increased joint stiffness in the drop-step only during backward trunk-leaning. The Step main effect revealed significantly increased peak hip and ankle extension moments in the drop-step, signifying pronounced mechanical demands on these joints. The Posture main effect revealed significantly higher and lower PFJ kinetics during backward and forward trunk-leaning, respectively, when compared with the self-selected condition. Forward trunk-leaning yielded significantly lower peak knee extension moments and higher hip extension moments, whereas the opposite effects occurred with backward trunk-leaning. Overall, changes to the running posture, but not to the running surface height, influenced the PFJ kinetics. In line with the previously reported efficacy of forward trunk-leaning in mitigating PFJ stress while even or decline running, this technique, through a distal-to-proximal joint load redistribution, also seems effective during running on surfaces with height perturbations.
... The decrease of the vertical amplitude of the CoM PACS with both trunk and head fixed to look at the ball reveals a lower limb pattern altered in PC. Numerous research studied the impact of the trunk posture on gait pattern, whether for medical purposes [42] or sport performance purposes [43,44]. These studies showed that a modification of trunk posture on the frontal and sagittal plane influences the bilateral lower limb kinematics and muscle activity. ...
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Team lifting is a complex and collective motor task comprising motor and cognitive components. The purpose of this research is to investigate how individual and collective performances are impacted during load transport combined with a cognitive task. Ten dyads performed a first condition in which they transported a load (CC), and a second one in which they transported the load while maintaining a ball on its top (PC). The recovery-rate, amplitude and period of the centre-of-mass (COM) trajectory were computed for the system (dyad + table = PACS). We analysed the forces and moments exerted at each joint of the upper limbs of the participants. We observed a decrease in the overall performance of the dyads during PC: (i) the velocity and amplitude of CoMPACS decreased by 1.7% and 5.8%, respectively, (ii) inter-participant variability of the Moment-Cost-Function and recovery rate decreased by 95%, and 19.2%, respectively during PC. Kinetic synergy analysis showed that the participants reorganized their coordination in the PC. We demonstrated that adding a precision task affects the economy of collective load carriage at the PACS level while the upper-limbs joint moments were better balanced across the paired participants for the PC.
... In contrast to these findings, there was no difference in trunk inclination between the n-IP and IP groups. The runners had not trained before the data acquisition, so fatigue was not an important factor [38,39]. The WalkerView can easily detect trunk inclination, and therefore, it can easily educate recreational runners to increase trunk flexion and reduce patellofemoral joint stress, as the literature suggests [34,35]. ...
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Running is a physical activity and the investigation of its biomechanical aspects is crucial both to avoid injuries and enhance performance. Recreational runners may be liable to increased stress over the body, particularly to lower limb joints. This study investigates the different running patterns of recreational runners by analyzing characteristics of the footwear impact peak, spatiotemporal, and kinematic parameters among those that present with a peak impact and those that do not, with a 3D markerless system. Thirty recreational runners were divided into two groups: impact peak group (IP) (n = 16) and no impact peak group (n = 14) (n-IP). Kinematic and spatiotemporal parameters showed a large Cohen’s d effect size between the groups. The mean hip flexion was IP 40.40° versus n-IP 32.30° (d = −0.82). Hip extension was IP 30.20° versus n-IP 27.70° (d = −0.58), and ankle dorsiflexion was IP 20.80°, versus n-IP 13.37° (d = −1.17). Stride length was IP 117.90 cm versus n-IP 105.50 cm (d = −0.84). Steps per minute was IP group 170 spm, versus n-IP 163 spm (d = −0.51). The heel-to-toe drop was mainly 10–12 mm for the IP group and 4–6 mm for the n-IP group. Recreational runners whose hip extension is around 40°, ankle dorsiflexion around 20°, and initial foot contact around 14°, may be predisposed to the presence of an impact peak.
... Previous studies report impaired trunk flexion with rotation strength [7] and kinematic changes in terms of increased trunk flexion during stair descent in participants with PFP [46]. The reason for this may lay in the fact that forward trunk lean during walking and running has been proposed as an effective strategy to reduce PFJ stress [47]. Although these conclusions may be important factors in designing rehabilitation programs, improvements in PFP symptoms seem to be more related to gains in strength than changes in kinematic behavior [48]. ...
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Patellofemoral pain (PFP) is a frequent knee condition. The aim of this study was to investigate strength, flexibility and postural control in people with and without PFP. Fifty-five participants between 14 and 54 years of age (PFP = 18, control group = 37) were included. Strength and flexibility for all trunk, hip, knee and ankle muscle groups were measured along with postural control outcomes. Analyses were conducted based on the “affected” and “non-affected” leg within-group and between-groups. Between-groups analysis demonstrated a statistically lower strength of trunk muscles (range: 35.8–29.3%, p < 0.001), knee extensors (20.8%, p = 0.005) and knee flexors (17.4%, p = 0.020) in PFP participants. Within-group analysis proved an 8.7% (p = 0.018) greater hip internal rotation strength and ankle extension flexibility (p = 0.032) of the “affected side” in PFP participants. This was, to our knowledge, the first study to investigate the strength of all trunk muscle groups. The results indicate that participants with PFP exhibit impaired strength of trunk muscle groups, along with knee muscle deficits, which may present a rehabilitation target. Clinicians should consider implementing trunk strengthening exercises into PFP programs along with knee-targeting exercise programs.
... 3,4 Identified causes of knee injury in sport are many and include diminished lower-extremity strength, 5,6 poor balance and/or proprioception, 7-10 and movement behaviors that increase knee loading. [10][11][12][13][14] With respect to movement behavior and knee injury, performing athletic tasks with elevated knee extensor moments increases load on the patellar tendon, 15 patellofemoral joint, 16 and the anterior cruciate ligament (ACL). 17,18 In addition, high knee extensor moments have been found to predict ACL injury. ...
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Given that increased use of the knee extensors relative to the hip extensors may contribute to various knee injuries, there is a need for a practical method to characterize movement behavior indicative of how individuals utilize the hip and knee extensors during dynamic tasks. The purpose of the current study was to determine whether the difference between sagittal plane trunk and tibia orientations obtained from 2D video (2D trunk–tibia) could be used to predict the average hip/knee extensor moment ratio during athletic movements. Thirty-nine healthy athletes (15 males and 24 females) performed 6 tasks (step down, drop jump, lateral shuffle, deceleration, triple hop, and side-step-cut). Lower-extremity kinetics (3D) and sagittal plane video (2D) were collected simultaneously. Linear regression analysis was performed to determine if the 2D trunk–tibia angle at peak knee flexion predicted the average hip/knee extensor moment ratio during the deceleration phase of each task. For each task, an increase in the 2D trunk–tibia angle predicted an increase in the average hip/knee extensor moment ratio when adjusted for body mass (all P < .013, R ² = .17–.77). The 2D trunk–tibia angle represents a practical method to characterize movement behavior that is indicative of how individuals utilize the hip and knee extensors during dynamic tasks.
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The purpose of this study was to determine the influence of frontal and transverse plane rotations of the femur and tibia on peak maximum principal stress in the patellar tendon. Using finite element modeling, patellar tendon stress profiles of 8 healthy individuals were obtained during a simulated squatting task (45° of knee flexion). The femur and tibia of each model were rotated 10° (in 2° increments) along their respective axes beyond that of the natural degree of rotation. This process was repeated for the transverse plane (internal and external rotation) and frontal plane (adduction and abduction). Quasi‐static loading simulations were performed to quantify peak maximum principal stress in patellar tendon. Internal and external rotations of the femur and tibia that exceeded 4 degrees beyond that of the natural rotation resulted in progressively greater patellar tendon stress (p<0.05). Incremental femur and tibia adduction and abduction resulted in an increase in patellar tendon stress, but only at the end range of motions evaluated. These results suggest that tibiofemoral rotations in the frontal and transverse planes have the potential to influence patellar tendon stress. In particular, patellar tendon stress is highly sensitive to small degrees of tibia and/or femur motions in the transverse plane. This article is protected by copyright. All rights reserved.
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Objective: To systematically review and synthesise patellofemoral joint reaction force (PFJRF) in healthy individuals and those with patellofemoral pain and osteoarthritis (OA), during everyday activities, therapeutic exercises and with physical interventions (eg, foot orthotics, footwear, taping, bracing). Design: A systematic review with meta-analysis. Data sources: Medline, Embase, Scopus, CINAHL, SportDiscus and Cochrane Library databases were searched. Eligibility criteria: Observational and interventional studies reporting PFJRF during everyday activities, therapeutic exercises, and physical interventions. Results: In healthy individuals, the weighted average of mean (±SD) peak PFJRF for everyday activities were: walking 0.9±0.4 body weight (BW), stair ascent 3.2±0.7 BW, stair descent 2.8±0.5 BW and running 5.2±1.2 BW. In those with patellofemoral pain, peak PFJRF were: walking 0.8±0.2 BW, stair ascent 2.5±0.5 BW, stair descent 2.6±0.5 BW, running 4.1±0.9 BW. Only single studies reported peak PFJRF during everyday activities in individuals with patellofemoral OA/articular cartilage defects (walking 1.3±0.5 BW, stair ascent 1.6±0.4 BW, stair descent 1.0±0.5 BW). The PFJRF was reported for many different exercises and physical interventions; however, considerable variability precluded any pooled estimates. Summary: Everyday activities and exercises involving larger knee flexion (eg, squatting) expose the patellofemoral joint to higher PFJRF than those involving smaller knee flexion (eg, walking). There were no discernable differences in peak PFJRF during everyday activities between healthy individuals and those with patellofemoral pain/OA. The information on PFJRF may be used to select appropriate variations of exercises and physical interventions.
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Background Traditional running gait analysis is limited to artificial environments, but whether treadmill running approximates overground running is debated. This study aimed to compare treadmill gait analysis using fixed video with outdoor gait analysis using drone video capture. Hypothesis Measured kinematics would be similar between natural outdoor running and traditional treadmill gait analysis. Study Design Crossover study. Level of Evidence Level 2. Methods The study population included cross-country, track and field, and recreational athletes with current running mileage of at least 15 km per week. Participants completed segments in indoor and outdoor environments. Indoor running was completed on a treadmill with static video capture, and outdoor segments were obtained via drone on an outdoor track. Three reviewers independently performed clinical gait analysis on footage for 32 runners using kinematic measurements with published acceptable intra- and interrater reliability. Results Of the 8 kinematic variables measured, 2 were found to have moderate agreement indoor versus outdoor, while 6 had fair to poor agreement. Foot strike at initial contact and rearfoot position at midstance had moderate agreement indoor versus outdoor, with a kappa of 0.54 and 0.49, respectively. The remaining variables: tibial inclination at initial contact, knee flexion angle initial contact, forward trunk lean full gait cycle, knee center position midstance, knee separation midstance, and lateral pelvic drop at midstance were found to have fair to poor agreement, ranging from 0.21 to 0.36. Conclusion This study suggests that kinematics may differ between natural outdoor running and traditional treadmill gait analysis. Clinical Relevance Providing recommendations for altering gait based on treadmill gait analysis may prove to be harmful if treadmill analysis does not approximate natural running environments. Drone technology could provide advancement in clinical running recommendations by capturing runners in natural environments.
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Team lifting is a complex and collective motor task that possesses both motor and cognitive components. The purpose of this study was to investigate to what extent the biomechanics of a collective load carriage is affected when a dyad of individuals is performing a carrying task with an additional accuracy constraint. Ten dyads performed a first condition in which they collectively transported a load (CC), and a second one in which they transported the same load while maintaining a ball in a target position on its top (PC). The recovery-rate, amplitude, and period of the center-of-mass (COM) trajectory were computed for the whole system (dyad + table = PACS). We analyzed the forces and moments exerted at each joint of the upper limbs of the subjects. We observed a decrease in the overall performance of the dyads when the Precision task was added, i.e., i) the velocity and amplitude of CoM PACS decreased by 1,7% and 5,8%, respectively, ii) inter-subject variability of the Moment-Cost-Function decreased by 95% and recovery rate decreased by 19,2% during PC. A kinetic synergy analysis showed that the subjects reorganized their coordination in the PC. Our results demonstrate that adding a precision task affects the economy of collective load carriage. Notwithstanding, the joint moments at the upper-limbs are better balanced and co-vary more across the paired subjects during the precision task. Our study results may find applications in domains such as Ergonomics, Robotics-developments, and Rehabilitation.
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The purpose of this study was to compare three different intervals for a between sets rest period during a common isokinetic knee extension strength-testing protocol of twenty older Brazilian men (66.30 ± 3.92 yrs). The volunteers underwent unilateral knee extension (Biodex System 3) testing to determine their individual isokinetic peak torque at 60, 90, and 120°s(-1). The contraction speeds and the rest periods between sets (30, 60 and 90 s) were randomly performed in three different days with a minimum rest period of 48 hours. Significant differences between and within sets were analyzed using a One Way Analysis of Variance (ANOVA) with repeated measures. Although, at angular velocity of 60°s(-1) produced a higher peak torque, there were no significant differences in peak torque among any of the rest periods. Likewise, there were no significant differences between mean peak torque among all resting periods (30, 60 and 90s) at angular velocities of 90 and 120°s(-1). The results showed that during a common isokinetic strength testing protocol a between set rest period of at least 30 s is sufficient for recovery before the next test set in older men. Key PointsThe assessment of muscular strength using isokinetics muscle contraction in older individuals is very important for exercise prescription and rehabilitation.The minimal time between intraset isokinetics knee extension assessment in older individuals need to be more investigated, however 30 s appear to besufficient time for strength recover.
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Study design: Observational. Objectives: To compare lower extremity negative joint work and vertical ground reaction force loading rates in rearfoot-striking (RS) and Chi runners. Background: Alternative running styles such as Chi running have become a popular alternative to RS running. Proponents assert that this running style reduces knee joint loading and ground reaction force loading rates. Methods: Twenty-two RS and 12 Chi runners ran for 5 minutes at a self-selected speed on an instrumented treadmill. A 3-D motion analysis system was used to obtain kinematic data. Average vertical ground reaction force loading rate and negative work of the ankle dorsiflexors, ankle plantar flexors, and knee extensors were computed during the stance phase. Groups were compared using a 1-way analysis of covariance for each variable, with running speed and age as covariates. Results: On average, RS runners demonstrated greater knee extensor negative work (RS, -0.332 J/body height × body weight [BH·BW]; Chi, -0.144 J/BH·BW; P<.001), whereas Chi runners demonstrated more ankle plantar flexor negative work (Chi, -0.467 J/BH·BW; RS, -0.315 J/BH·BW; P<.001). RS runners demonstrated greater average vertical ground reaction force loading rates than Chi runners (RS, 68.6 BW/s; Chi, 43.1 BW/s; P<.001). Conclusion: Chi running may reduce vertical loading rates and knee extensor work, but may increase work of the ankle plantar flexors.
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Increasing step rate has been shown to elicit changes in joint kinematics and kinetics during running, and has been suggested as a possible rehabilitation strategy for runners with patellofemoral pain. The purpose of this study was to determine how altering step rate affects internal muscle forces and patellofemoral joint loads, and then to determine what kinematic and kinetic factors best predict changes in joint loading. We recorded whole body kinematics of 30 healthy adults running on an instrumented treadmill at three step rate conditions (90%, 100%, and 110% of preferred step rate). We then used a 3D lower extremity musculoskeletal model to estimate muscle, patellar tendon, and patellofemoral joint forces throughout the running gait cycles. Additionally, linear regression analysis allowed us to ascertain the relative influence of limb posture and external loads on patellofemoral joint force. Increasing step rate to 110% of preferred reduced peak patellofemoral joint force by 14%. Peak muscle forces were also altered as a result of the increased step rate with hip, knee and ankle extensor forces, and hip abductor forces all reduced in mid-stance. Compared to the 90% step rate condition, there was a concomitant increase in peak rectus femoris and hamstring loads during early and late swing, respectively, at higher step rates. Peak stance phase knee flexion decreased with increasing step rate, and was found to be the most important predictor of the reduction in patellofemoral joint loading. Increasing step rate is an effective strategy to reduce patellofemoral joint forces and could be effective in modulating biomechanical factors that can contribute to patellofemoral pain.
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Elevated patellofemoral joint stress is thought to contribute to the development and progression of patellofemoral pain syndrome. The purpose of this study was to determine if running barefoot decreases patellofemoral joint stress in comparison to shod running. Lower extremity kinematics and ground reaction force data were collected from 22 trained runners during overground running while barefoot and in a neutral running shoe. The kinematic and kinetic data were used as input variables into a previously described mathematical model to determine patellofemoral joint stress. Knee flexion angle, net knee extension moment and the model outputs of contact area, patellofemoral joint reaction force and patellofemoral joint stress were plotted over the stance phase of the gait cycle and peak values compared using paired t tests and standardised mean differences calculated. Running barefoot decreased peak patellofemoral joint stress by 12% (p=0.000) in comparison to shod running. The reduction in patellofemoral joint stress was a result of reduced patellofemoral joint reaction forces (12%, p=0.000) while running barefoot. Elevated patellofemoral joint stress during shod running might contribute to patellofemoral pain. Running barefoot decreases patellofemoral joint stress.
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Purpose: Knee pain and Achilles tendinopathies are the most common complaints among runners. The differences in the running mechanics may play an important role in the pathogenesis of lower limb overuse injuries. However, the effect of a runner's foot strike pattern on the ankle and especially on the knee loading is poorly understood. The purpose of this study was to examine whether runners using a forefoot strike pattern exhibit a different lower limb loading profile than runners who use rearfoot strike pattern. Methods: Nineteen female athletes with a natural forefoot strike (FFS) pattern and pair-matched women with rearfoot strike (RFS) pattern (n = 19) underwent 3-D running analysis at 4 m·s⁻¹. Joint angles and moments, patellofemoral contact force and stresses, and Achilles tendon forces were analyzed and compared between groups. Results: FFS demonstrated lower patellofemoral contact force and stress compared with heel strikers (4.3 ± 1.2 vs 5.1 ± 1.1 body weight, P = 0.029, and 11.1 ± 2.9 vs 13.0 ± 2.8 MPa, P = 0.04). In addition, knee frontal plane moment was lower in the FFS compared with heel strikers (1.49 ± 0.51 vs 1.97 ± 0.66 N·m·kg⁻¹, P =0.015). At the ankle level, FFS showed higher plantarflexor moment (3.12 ± 0.40 vs 2.54 ± 0.37 N·m·kg⁻¹; P = 0.001) and Achilles tendon force (6.3 ± 0.8 vs 5.1 ± 1.3 body weight; P = 0.002) compared with RFS. Conclusions: To our knowledge, this is the first study that shows differences in patellofemoral loading and knee frontal plane moment between FFS and RFS. FFS exhibit both lower patellofemoral stress and knee frontal plane moment than RFS, which may reduce the risk of running-related knee injuries. On the other hand, parallel increase in ankle plantarflexor and Achilles tendon loading may increase risk for ankle and foot injuries.