Journal of Athletic Training 201449(6):723732 [603245]

Journal of Athletic Training 2014;49(6):723–732
doi: 10.4085/1062-6050-49.3.29
/C211by the National Athletic Trainers’ Association, Inc
www.natajournals.orgoriginal research
Altered Knee and Ankle Kinematics During Squatting
in Those With Limited Weight-Bearing–Lunge Ankle-
Dorsiflexion Range of Motion
Karli E. Dill, MA, ATC*; Rebecca L. Begalle, PhD, ATC †; Barnett S. Frank, MA,
LAT, ATC*; Steven M. Zinder, PhD, ATC ‡; Darin A. Padua, PhD, ATC*
*Department of Exercise and Sport Science, University of North Carolina at Chapel Hill; †School of Kinesiology and
Recreation, Illinois State University, Normal; ‡Department of Orthopaedics and Sports Medicine, Morsani College ofMedicine, University of South Florida, Tampa
Context: Ankle-dorsiflexion (DF) range of motion (ROM)
may influence movement variables that are known to affect
anterior cruciate ligament loading, such as knee valgus andknee flexion. To our knowledge, researchers have not studiedindividuals with limited or normal ankle DF-ROM to investigatethe relationship between those factors and the lower extremitymovement patterns associated with anterior cruciate ligament
injury.
Objective: To determine, using 2 different measurement
techniques, whether knee- and ankle-joint kinematics differ
between participants with limited and normal ankle DF-ROM.
Design: Cross-sectional study.
Setting: Sports medicine research laboratory.
Patients or Other Participants: Forty physically active
adults (20 with limited ankle DF-ROM, 20 with normal ankle
DF-ROM).
Main Outcome Measure(s): Ankle DF-ROM was assessed
using 2 techniques: (1) nonweight-bearing ankle DF-ROM withthe knee straight, and (2) weight-bearing lunge (WBL). Kneeflexion, knee valgus-varus, knee internal-external rotation, andankle DF displacements were assessed during the overhead-squat, single-legged squat, and jump-landing tasks. Separate 1-
way analyses of variance were performed to determine whetherdifferences in knee- and ankle-joint kinematics existed between
the normal and limited groups for each assessment.
Results: We observed no differences between the normal
and limited groups when classifying groups based on non-
weight-bearing passive-ankle DF-ROM. However, individuals
with greater ankle DF-ROM during the WBL displayed greaterknee-flexion and ankle-DF displacement and peak knee flexionduring the overhead-squat and single-legged squat tasks. In
addition, those individuals also demonstrated greater knee-
varus displacement during the single-legged squat.
Conclusions: Greater ankle DF-ROM assessed during the
WBL was associated with greater knee-flexion and ankle-DF
displacement during both squatting tasks as well as greaterknee-varus displacement during the single-legged squat. As-sessment of ankle DF-ROM using the WBL provided important
insight into compensatory movement patterns during squatting,
whereas nonweight-bearing passive ankle DF-ROM did not.Improving ankle DF-ROM during the WBL may be an importantintervention for altering high-risk movement patterns commonly
associated with noncontact anterior cruciate ligament injury.
Key Words: knee flexion, knee valgus, knee varus, anterior
cruciate ligament, squat, jump landing
Key Points
/C15Nonweight-bearing ankle-dorsiflexion range of motion was not associated with changes in ankle or knee kinematics
during the overhead-squat, single-legged squat, or jump-landing task.
/C15Greater ankle-dorsiflexion range of motion during the weight-bearing lunge resulted in greater sagittal-plane motionat the knee and ankle during the squatting tasks but not the jump landing.
/C15Compared with nonweight-bearing passive measures, ankle-dorsiflexion range of motion during the weight-bearinglunge may be a more sensitive measure for identifying those with high-risk movement patterns.
An estimated 350 000 anterior cruciate ligament
(ACL) reconstructions are performed annually in
the United States,1with most of those injuries
occurring during sport participation by individuals between15 and 25 years old.
2,3Recent estimates have illustrated a
national increase in ACL injuries of 67.8% during a 10-yearperiod.
4In addition to those concerning numbers, 70% of
ACL injuries result from noncontact mechanisms , defined as
no contact with another player or piece of equipment, such asplant-and-cut maneuvers, landing from a jump, and deceler-ating.
5,6The high incidence of noncontact ACL injury is
driving researchers to investigate possible biomechanical andneuromuscular factors that may contribute to ACL injury.
Dynamic maneuvers, such as the overhead-squat (OHS),
7
single-legged squat (SLS),8and jump-landing (JL)9tasks,
have been used in laboratory and clinical settings toelucidate faulty lower extremity movement patterns and to
identify individuals potentially at risk for ACL injury.
Some of the key patterns of movement identified are side-to-side (frontal-plane) or rot ational (transverse-plane)
Journal of Athletic Training 723

movements at the knee because those movements place the
greatest load on the ACL in combination with an anteriortibial shear force (sagittal plane).
10Anterior cruciate
ligament loading is exacerbated when the knee is in aminimally flexed or hyperextended position in conjunctionwith a large quadriceps muscle contraction.
11,12Noncontact
ACL injury mechanisms are often described as landing in arelatively extended knee position (sagittal plane) combinedwith frontal- and transverse-plane loading.
12Movement at
adjacent joints also influences knee loading. Research-ers
7,13,14have identified a potential relationship between
limited dorsiflexion range of motion (DF-ROM) in theankle and knee kinematics, such as medial knee displace-ment, which may increase the risk of ACL injury. Ideally,those squatting and JL movements would include primarily
sagittal-plane motion at all lower extremity joints to
perform properly and absorb and dissipate the landingforces.
15Restrictions in the ability to move through ankle
DF during weight bearing can interfere with performanceby potentially increasing the plantar-flexion moment whenthe ankle is dorsiflexed
16and restricting the forward
rotation of the shank at the ankle when the foot is incontact with the ground.
17Limitations in ankle-DF
displacement are often accompanied by less sagittal-planemotion at proximal joints, such as the knee and trunk.
15,18
Therefore, ankle-DF restrictions may contribute to limitedsagittal-plane motion at the knee and thereby contribute tocompensatory increases in frontal- and transverse-planemotions that are potentially injurious to the ACL.
Less DF-ROM assessed passively in a nonweight-bearing
(NWB) position has been associated with greater medial-knee displacement during a variety of tasks.
7,14Bell et al7
studied individuals with medial-knee displacement, whichis a clinical observation of dynamic valgus collapse, andobserved that participants who displayed medial-kneedisplacement during an OHS had approximately 20% lessNWB, passive ankle DF than did those participants withoutmedial-knee displacement. Furthermore, the medial-kneedisplacement observed during the OHS was corrected whena 2-in (5.08-cm) lift was placed under the heel; thecorrection may have occurred because of the increasedtibial angle in the anterior direction. Less passive DF-ROMassessed in NWB movements has also been associated with
greater frontal-plane knee excursion during a double-legged
drop-landing in young female soccer players
14and with
decreased knee-flexion displacement during a jump-landingtask.
19
Other authors have investigated ankle-DF motion during
dynamic movements in relation to knee kinematics, withcontrasting findings. Compared with men, women withgreater DF-ROM measured during SLS
20and double-
legged drop landings21demonstrated greater maximum
knee-valgus angles. This body of research suggests thatankle DF-ROM may contribute to the amount of kneevalgus (frontal plane) and knee flexion (sagittal plane) an
individual uses during dynamic movement, but the
relationship is unclear and requires further investigation.
Previous examinations
7,14,19of the relationship between
ankle DF-ROM and knee kinematics may be limitedbecause of the NWB, passive assessments that were oftenused. Weight-bearing measures of ankle DF-ROM mayprovide a better representation of the available ROM duringfunctional, weight-bearing tasks.
22However, previousauthors have not, to our knowledge, investigated the
relationship between knee kinematics during dynamicmovement and separate weight-bearing and NWB ankle
DF-ROM assessments. In addition, no previous researchers,
to our knowledge, have intentionally recruited a participant
population with known limitations in ankle DF-ROM.
Therefore, the purpose of our study was to investigate knee
and ankle kinematics during dynamic tasks in participants
who were identified as having limited ankle DF-ROM andto compare the results with those of participants who had
normal ankle DF-ROM. Ankle-DF motion was assessed
passively through both weight-bearing and NWB tech-
niques before testing, and total displacement during
dynamic movement was calculated. The goal of comparing
the ROM of normal and limited groups was to find an
assessment that could be used clinically to indicate how an
individual will perform during a more functional task. We
hypothesized that individuals with less DF-ROM, bothNWB and weight bearing, would display kinematics
associated with ACL loading (less sagittal-plane motion
and greater frontal-plane motion) during an OHS, SLS, and
JL task.
METHODS
Participants
Initial group allocation was determined through a
screening process performed by the primary researcher
(K.E.D.) using an NWB measure of passive ankle DF-ROMwith the knee extended. We chose this measurement for
participant recruitment because we had identified cutoff
angles derived from Moseley et al,
17based on their data
classifying individuals as normal (11.2 8–25.08) or inflexible
(4.38–11.28). We wanted a clear separation between our
participant groups, so we initially used the high (25 8) and
low (5 8) values as our criteria. However, through pilot
testing, we found it very difficult to locate individuals with
258of ankle DF-ROM assessed with the knee extended and
lowered the cutoff point to 15 8for this study. These cutoff
points (normal, /C21158; limited, /C2058) allowed us to create
groups with distinctly different and nonoverlapping pas-
sive-ankle DF-ROM during participant recruitment. In a
separate testing session, ankle DF-ROM was assessed using
2 techniques: (1) NWB knee extended and (2) weight-
bearing lunge to reclassify participants into normal andlimited groups to investigate differences in knee and ankle
kinematics during functional tasks. The measurements
obtained during the testing session are reported.
Forty physically active participants, 20 men and 20
women, were identified through a larger screening of 67individuals who volunteered to participate in this research
study and met the inclusion criteria. In total, 10 men and 10
women were allocated to both the normal and limited-
motion groups.
Participant demographics are depicted in Table 1. All
participants were physically active , which was defined as
30 minutes of moderate physical activity at least 3 times perweek. Volunteers were excluded from this study if they had
a NWB, passive-ankle DF-ROM measurement between 6 8
and 14 8; a history of any lower extremity surgical
procedure; a history of a lower extremity injury during
the previous 6 months that limited their physical activity for
724 Volume 49 /C15Number 6 /C15December 2014

2 or more days; or a known neurologic disorder. Before
data collection, each participant read and signed aninformed consent document approved by the university’sinstitutional review board (which also approved the study)and completed a general medical history form to verifyinclusion criteria.
Instrumentation
We took NWB ankle DF-ROM measures with a standard,
19-in (0.48-m), plastic goniometer for the screening andagain during the testing session.
23Ankle DF-ROM during
the weight-bearing lunge (WBL) was measured using adigital inclinometer (The Saunders Group, Chaska, MN).
22
Knee and ankle kinematics were captured using an
electromagnetic motion-tr acking system (Motion Star;
Ascension Technology Corporation, Milton, VA) at asampling frequency of 140 Hz. All kinematic and kineticdata were processed using MotionMonitor Software(Innovative Sports Training, Inc, Chicago, IL) and wereexported into a customized software program (MATLAB11; MathWorks, Natick, MA) for data reduction. We used a
nonconductive force plate (Bertec Corp, Columbus, OH) to
collect kinetic data sampled at 1400 Hz to determine initialcontact during the JL task.
Screening Session
For screening, each potential participant’s NWB ankle
DF-ROM was assessed for the dominant leg with theparticipant lying supine on a treatment table (Figure 1). The
dominant leg was defined as the leg used to kick a ball for
maximum distance, and all testing was performed on thatextremity. The examiner moved the ankle into plantar
flexion and then placed the ankle in a subtalar-neutral
position using palpation. He or she passively dorsiflexed theankle, while maintaining a subtalar-neutral position, until
the point of first resistance. At that point, the examiner
measured the angle formed by the shaft of the fibula and thelateral midline of the foot using a standard goniometer.
24
That assessment was performed with the subtalar joint in
neutral to avoid movement compensations at the subtalar
and midtarsal joints and to effectively evaluate talocruraljoint motion. The participants who met the inclusioncriteria (normal, /C21158; limited, /C2058) were asked to
schedule a separate testing session.
Testing Procedures
Once participants were identified and assigned to a group
through the initial screening, they reported to the laboratoryfor a single testing session with the primary researcher
(K.E.D.). She recorded height and body mass for each
participant, who then completed a 5-minute, upper body,cardiovascular warm-up on a stationary bicycle at moderate
intensity as determined by a rate of perceived exertion of 3
of 10. An upper-body warm-up was chosen so that theROM assessments would not be influenced by pedaling abicycle with the lower extremities.
Ankle DF-ROM was assessed using both an NWB
method and a WBL method performed in randomizedorder. The NWB ankle DF-ROM method involved the same
testing procedure used in the screening session. Three trials
were recorded for the dominant leg, and the arithmeticmean was used for data analysis. The measurements
recorded during this testing session confirmed group
allocation and were used for data analysis; ie, allmeasurements were taken on the same day.
The weight-bearing method used the WBL test (Figure
2). To perform the WBL, the participant was asked to placethe foot perpendicular to the wall with the second toe and
midline of the heel placed directly on a piece of guide tape
placed on the floor. He or she was then instructed to lungethe knee forward toward the wall until maximum ankle DF
was reached, which was identified as the heel lifting off the
ground. If the knee contacted the wall, the foot was moved
posteriorly until the maximum range of DF was achieved.The examiner placed a digital inclinometer distal to theTable 1. Participant Demographics by Groupa
CharacteristicAssessment
Nonweight-Bearing Position Weight-Bearing Lunge
Normal (n ¼20) Limited (n ¼20) Normal (n ¼20) Limited (n ¼20)
Ankle-dorsiflexion criteria, 8 /C2115 /C205 /C2144 /C2043
Mean 6SD
Age, y 20.70 61.98b19.45 61.40b20.70 61.95b19.45 61.43b
Height, cm 172.33 69.73 171.12 68.64 170.22 69.77 173.23 68.34
Mass, kg 70.13 613.80 70.42 612.50 67.77 614.10 72.78 611.60
Ankle-dorsiflexion range of motion, 8 16.78 62.16c1.6362.58c50.84 65.16c38.91 63.48c
aTwelve of 40 participants (30%) switched groups (70% remained in the same group).
bGroup differences, P,.05.
cGroup differences, P,.001.
Figure 1. Nonweight-bearing ankle-dorsiflexion range-of-motion
assessment.
Journal of Athletic Training 725

tibial tuberosity to measure the angle of the tibia relative to
vertical with the heel in contact with the ground.22The
position of the subtalar joint was not controlled during this
assessment, which is similar to the way the test is often
performed clinically. The examiner took the measurement 3
times on the dominant leg and recorded the arithmetic mean
for data analysis. Before testing, we established the
intrarater reliability for the investigator performing all
measurements (K.E.D.) and demonstrated excellent reli-
ability for the NWB DF-ROM (intraclass correlationcoefficient [3,k], 0.988; standard error of measurement,
0.888) and WBL (intraclass correlation coefficient [3,k],
0.953; standard error of measurement, 1.61 8) tests.
After the examiner recorded the ROM measurements, she
prepared the participant for motion-analysis data collection.
Electromagnetic tracking sensors were placed on the skin
with double-sided tape and secured with prewrap and
athletic tape. The sensors were placed unilaterally on thedominant leg over the midshaft of the second-third
metatarsals of the foot, anteromedial aspect of the proximal
tibia, lateral aspect of the thigh, and the spinous process of
L5. The shoe was unlaced, and the tongue was pulled
forward and fastened to the top of the shoe with double-
sided tape to expose the dorsum of the foot and allow
sensor placement. The shoe was then relaced up the side, sothat no laces crossed over to the opposite side and
potentially touched the sensor. The shoelace was tied
together once it reached the top of the shoe to ensure proper
fit. This procedure was performed as in previous research
25
to allow space for the sensor on the foot and to permit theparticipant to wear an athletic shoe to perform the double-
legged JL. Participants wore their own athletic shoes but
did not wear socks so the sensor could be firmly attached to
the skin. The shoes were removed for the SLS and OHS bysimply untying the top bow and sliding the foot out, without
disrupting the sensor placement, to allow for barefoot
completion of those 2 tasks. The space gained by removing
the tongue of the sneaker was ample for the sensor, which
was approximately 8 mm by 20 mm, so that no disruption
of the sensor occurred. The sensor data, which indicated the
orientation and position of each sensor relative to astandard-range transmitter, were conveyed back to a
personal computer. The dominant limb was modeled by
digitizing 6 additional landmarks to define the hip-, knee-,
and ankle-joint centers. The knee-joint center was definedas the midpoint between the digitized medial and lateral
femoral condyles, and the ankle-joint center was defined as
the midpoint between the medial and lateral malleoli. Leftand right sides of the anterior-superior iliac spine weredigitized to determine the hip-joint center of rotation usingthe Bell et al
26method. Global and segment axis systems
were established with the x-axis designated as positive inthe anterior direction from the participant, the y-axispositive to the left, and the z-axis positive in the upwarddirection.
Each participant completed OHS, SLS, and JL tasks in a
randomized order. The OHS task was performed with thefeet shoulder-width apart, arms raised vertically overhead,heels on the ground, and squatting to at least 60 8of knee
flexion.
7The SLS was performed with the hands on the
hips, opposite leg raised in front of the participant with thefoot approximately 10 cm off the ground, squatting to atleast 60 8of knee flexion.
27A metronome set at 60 beats/
min was used to ensure similar cadences of the squatting
task for each participant. The examiner instructed partic-
ipants to descend as far as possible for 2 beats and to returnto the starting position in 2 beats.
27She ensured that each
participant reached at least 60 8of knee flexion and returned
to the starting position by viewing the knee-flexion curve inthe MotionMonitor immediately after each set of squats.The starting position for participants was in the sagittal-plane resting position during double-legged and single-legged stances for the OHS and SLS, respectively.Therefore, some participants were slightly hyperextended,and some were slightly flexed to start. The mean knee-
flexion angle in the starting position was 8 8for the OHS and
128for the SLS for both the normal and limited ROM
groups. There were no differences between groups forknee-flexion starting angles, regardless of the DF-ROMassessment used for grouping. Not all participants may havereturned to exactly 0 8, but the examiner ensured they
consistently returned to their starting positions because ourgoal was to capture the natural movement. Squat trials wereconsidered successful if the participant reached at least 60 8
of knee flexion, returned to the starting position, maintainedthe hands overhead or on the hips (OHS, SLS), maintained
the metronome cadence, and was able to maintain balance
during the SLS. Each participant performed 5 consecutivetrials of the OHS and SLS; the 3 middle trials were used fordata analysis. If necessary, the participant performedadditional trials of the task to ensure 3 successful trialswere captured.
The JL task consisted of the participant jumping from a
30-cm box placed at a distance of 50% of the standing
height away from the force plate, landing on the force plate,and immediately jumping vertically as high as possible. Heor she jumped horizontally from the box to the force plate.
9
The examiner orally instructed each participant on how tocomplete each task and allotted up to 5 practice trials ofeach task before collecting data. No additional oralinstructions were given during the data-collection trials. AJL trial was considered successful if the participant pushedequally off both feet when leaving the box, landed with thedominant foot in the center of the force plate, and did not
hesitate before jumping vertically for maximum height. The
investigator confirmed those criteria visually. Each partic-ipant performed 5 JL trials, and the middle 3 trials were
Figure 2. Weight-bearing lunge test.
726 Volume 49 /C15Number 6 /C15December 2014

used for data analysis. All participants were able to perform
3 successful trials.
A 1-minute rest period was allotted between the practice
trials and data-collection trials. Thirty seconds of rest wereprovided between trials of a task, and then 1 minute of rest
was provided between tasks.
Data Reduction and Analysis
We estimated 3-dimensional coordinates of the lower
extremity bony landmarks using the MotionMonitorsoftware. An embedded, right-handed, Cartesian-coordinate
system was defined for the foot, shank, thigh, and pelvis
segments to describe the 3-dimensional position andorientation of those segments. All kinematic data were
smoothed with a Butterworth fourth-order, zero-phase lag,
low-pass digital filter at 14.5 Hz.
9Kinematic and kinetic
data were reduced using custom MATLAB software. We
calculated 3-dimensional knee- and ankle-joint angles usinga Euler-angle sequence, rotating in an order of (1) flexion-
extension (y-axis), (2) valgus-varus (x-axis), and (3)
internal-external rotation (z-axis). Data were analyzed
during the descent phase of each task. During the squat
tasks, the descent phase was operationally defined as thetime from initiation of knee-flexion motion until the time of
peak knee flexion for each trial. During the JL, the descent
phase was operationally defined as the period from the first
time the vertical ground-reaction force exceeded 10 N until
the time of peak knee flexion. We calculated jointdisplacements during the descent phase of all tasks for
the following motions: knee flexion, knee valgus, knee
varus, knee internal rotation, knee external rotation, and
ankle DF. Joint-displacement values were calculated as the
difference between the peak angle achieved during thedescent phase and the starting angle or angle at initial
ground contact for the squat tasks and JL, respectively. The
joint-displacement values were calculated for each of themiddle 3 trials, and the arithmetic mean of those values was
used for analyses.
Statistical Analysis
We conducted separate 1-way analyses of variance, 1 for
each task, to analyze differences in knee- and ankle-kinematic displacements and peak values between groups
based on the NWB ankle DF-ROM measure (normal, n ¼
20; limited, n ¼20).
The 50th percentile was calculated for the WBL
measurements to determine the cutoff point that would
categorize all participants into 2 equal groups representing
normal and limited ROMs for this population. Separate 1-way analyses of variance, 1 for each task, were performed
to analyze differences in knee- and ankle-kinematic
displacements and peak values between groups based on
the WBL measure (normal, 20; limited, 20). Ankle DF-
ROM cutoff points for each group, along with means andstandard deviations, are depicted in Table 1. Most
participants (70%; 28 of 40) remained in the same group
(normal or limited) for both ankle DF-ROM assessments.
Six of the 40 participants (15%) were limited on NWB but
normal on WBL, whereas 6 other participants (15%) werenormal on NWB but limited on WBL.We set the a priori alevel at P¼.05 for all analyses. All
statistical analyses were performed using SPSS (version19.0; SPSS Inc, Chicago, IL).
RESULTS
No significant differences were observed between the
NWB DF-ROM groups before data collection in average
height ( P¼.68) or body mass ( P¼.95). The groups were
different in age (normal, 21 62 years; limited, 20 61
years; P¼.03); however, the mean difference in age was
1.25 years. Similarly, no height ( P¼.30) or body mass ( P¼
.23) differences were evident when we grouped participants
based on the WBL test. Means and standard deviations for
participant demographics for both group classifications are
reported in Table 1.
The NWB Ankle DF-ROM Group Classification
We observed no significant differences between the
normal and limited groups during the OHS (Table 2), SLS
(Table 3), or JL tasks (Table 4) for any joint-displacement
variable when participants were classified based on the
NWB ankle DF-ROM measure with the knee extended. No
significant differences were noted for peak joint angles.
The WBL Ankle DF-ROM Group Classification
Means, standard deviations, 95% confidence intervals,
and effect sizes for all joint-displacement variables during
the OHS, SLS, and JL tasks are reported in Tables 2
through 4, respectively. During the OHS (Table 2), the
normal group (WBL /C2144.028) displayed greater knee-
flexion displacement (mean difference, 14.94 8;F1,39¼
12.65; P¼.001) and greater ankle DF displacement (mean
difference, 7.89 8;F1,39¼21.21; P,.001) compared with
the limited group (WBL /C2044.018). During the SLS (Table
3), the normal group demonstrated greater knee-flexion
displacement (mean difference, 12.39 8;F1,39¼13.19; P¼
.001), greater ankle DF displacement (mean difference ¼
6.448;F1,39¼15.88; P,.001), and greater knee-varus
displacement (mean difference, 5.50 8;F1,39¼4.16; P¼
.048;) than the limited group.
Additionally, the normal group demonstrated greater
peak knee flexion during the OHS (normal, 112.71 86
13.488; limited, 97.45 8614.348; mean difference, 15.26 8;
F1,39¼12.02; P¼.001) and SLS (normal, 88.71 8612.738;
limited, 77.09 8610.208; mean difference, 11.62 8;F1,39¼
10.15; P¼.003) in comparison with the limited group. We
observed no group differences between knee-flexion angles
at the starting position for the OHS (normal, 8.04 867.848;
limited, 8.57 865.228; mean difference, 0.53 8;F1,39¼0.07;
P¼.800) or SLS (normal, 12.35 866.358; limited, 13.12 8
64.478; mean difference, 0.77 8;F1,39¼0.20; P¼.660). No
group differences were noted during the JL tasks (Table 4).
DISCUSSION
Our most important finding was that individuals with
limited ankle DF-ROM during the WBL demonstrated
altered knee- and ankle-joint kinematics. Specifically, thosewith limited ankle DF-ROM during the WBL displayed less
knee-flexion and ankle-DF displacement during the squat-
ting tasks. In addition, those same individuals showed
Journal of Athletic Training 727

Table 2. Overhead-Squat Lower Extremity Kinematics for Groups Based on the Nonweight-Bearing–Position and Weight-Bearing–Lunge Assessments
DisplacementaAnkle-Dorsiflexion Range of Motion
Nonweight-Bearing Position Weight-Bearing Lunge
Mean 6SD (95% Confidence Interval)
Effect SizeMean 6SD (95% Confidence Interval)
Effect Size Normal (n ¼20) Limited (n ¼20) Normal (n ¼20) Limited (n ¼20)
Knee flexion 100.38 613.73 (93.68, 107.08) 92.56 615.79 (85.87, 99.26) 0.53 103.94 611.79b(98.42, 109.46) 89.00 614.62b(82.16, 95.85) 1.31
Knee valgus /C02.3663.86 (/C03.72,/C01.00) /C01.2961.72 (2.65, 0.07) 0.38 /C01.7263.60 (/C03.40,/C00.03) /C01.9362.37 (/C03.04,/C00.82) 0.07
Knee varus 13.41 610.47 (7.95, 18.87) 17.14 613.48 (11.68, 22.61) 0.31 15.47 69.09 (11.22, 19.73) 15.08 614.69 (8.20, 21.96) 0.03
Knee external rotation /C05.5967.82 (/C08.38,/C02.81) /C03.6063.80 (/C06.38,/C00.81) 0.34 /C04.6667.82 (/C08.32,/C01.00) /C04.5264.07 (/C06.43,/C02.62) 0.02
Knee internal rotation 14.87 614.92 (8.63, 21.11) 11.11 612.56 (4.87, 17.36) 0.27 16.17 613.03 (10.07, 22.27) 9.82 614.02 (3.25, 16.38) 0.47
Ankle dorsiflexion /C030.03 67.45 (/C032.96, /C027.11) /C026.14 65.28 (/C029.06, /C023.21) 0.61 /C032.03 66.36b(/C035.01, /C029.05) /C024.14 64.27b(/C026.14, /C022.15) 1.49
aKinematic sign convention: ț, knee flexion, knee varus, and knee internal rotation; /C0, knee valgus, knee external rotation, and ankle dorsiflexion.
bGroup differences, P/C20.001.
Table 3. Single-Legged Squat Lower Extremity Kinematics for Groups Based on the Nonweight-Bearing–Position and Weight-Bearing–Lunge Assessment s
DisplacementaAnkle-Dorsiflexion Range of Motion
Nonweight-Bearing Position Weight-Bearing Lunge
Mean 6SD (95% Confidence Interval)
Effect SizeMean 6SD (95% Confidence Interval)
Effect Size Normal (n ¼20) Limited (n ¼20) Normal (n ¼20) Limited (n ¼20)
Knee flexion 75.58 611.00 (67.02, 78.13) 67.74 613.42 (62.20, 73.30) 0.64 76.36 611.02b(71.20, 81.52) 63.97 610.55b(57.07, 67.64) 1.51
Knee valgus /C02.4462.74 (/C03.38,/C01.50) /C01.1561.08 (/C02.10,/C00.21) 0.67 /C01.8362.23 (/C02.87,/C00.78) /C01.7762.14 (/C02.76,/C00.77) 0.03
Knee varus 11.25 610.96 (7.19, 15.32) 10.45 66.40 (6.39, 14.52) 0.09 13.60 610.28c(8.80, 18.41) 8.10 66.32c(5.14, 11.06) 0.66
Knee external rotation /C06.3665.46 (/C08.74,/C03.97) /C05.3265.07 (/C07.71,/C02.94) 0.20 /C04.7963.96 (/C06.64,/C02.94) /C06.8966.18 (/C09.78,/C03.40) 0.41
Knee internal rotation 5.90 65.38 (3.84, 7.95) 4.04 63.51 (1.98, 6.09) 0.42 6.30 65.16 (3.89, 8.72) 3.63 63.56 (1.97, 5.30) 0.61
Ankle dorsiflexion /C029.02 65.84 (/C031.68, /C026.36) /C025.89 65.90 (/C028.54, /C023.23) 0.53 /C030.67 65.67b(/C033.33, /C028.02) /C024.23 64.49b(/C026.33, /C022.13) 1.86
aKinematic sign convention: ț, knee flexion, knee varus, and knee internal rotation; /C0, knee valgus, knee external rotation, and ankle dorsiflexion.
bGroup differences, P/C20.001.
cGroup differences, P,.05.
728 Volume 49 /C15Number 6 /C15December 2014

greater knee-varus displacement during the SLS. However,
we found no differences in knee and ankle displacement
between normal and limited groups when classifyinggroups based on NWB ankle DF-ROM measures. Gener-ally, these results support our hypothesis that restrictedankle DF-ROM results in altered lower extremity move-ment patterns during functional tasks, such as squatting;however, this does not appear to be the case for JL tasks.The method used to assess ankle DF-ROM influenced thestudy’s results as group differences in knee and anklekinematics during squattin g were only present when
identifying participants as limited based on WBL ankle
DF-ROM measurements.
Nonweight-bearing ankle DF-ROM measures have been
shown to influence lower extremity kinematics duringfunctional tasks. Thus, we were surprised to see nodifferences in lower extremity kinematics between normaland limited groups when classifying participants using theNWB ankle DF-ROM method. Fong et al
19observed
greater NWB ankle DF-ROM (assessed with the knee
straight) associated with greater knee flexion during a JLtask. Differences in the JL task performed may explain thecontrasting results between studies. In our study, partici-pants performed a landing from a 30-cm box followed byan immediate countermovement jump for maximal height.The participants in the research by Fong et al
19also
performed a similar landing from a box, but they did notincorporate a maximal vertical jump. Incorporating thecountermovement jump after the box landing may havelimited the amount of ankle-DF displacement after
impacting the ground because participants were attempting
to immediately recoil and jump for maximal vertical height,thus limiting our ability to detect group differences. Inaddition, Fong et al
19studied healthy, physically active
individuals with no known ROM restrictions and reported14.3865.58of DF-ROM assessed with the knee extended.
In the current study, we intentionally recruited individualswith known restrictions as well as individuals with normalROM. Our values for the same assessment were muchsmaller for our limited group (1.63 862.588) and larger for
our normal group (16.78 86 2.168). Those differences in
sample populations could certainly have contributed to
differences in the study results.
It is not clear why we did not see differences in lower
extremity kinematics during the squatting tasks whenclassifying participants based on NWB ankle DF-ROMmeasures. Bell et al
7reported decreased NWB ankle DF-
ROM in those who displayed medial knee displacement
(knee-valgus collapse) during a double-legged squat
compared with those who did not. Mauntel et al27observed
similar findings in those who demonstrated medial kneedisplacement during an SLS task. The NWB ankle DF-ROM measure and squat tasks we used were nearlyidentical to those reported by Bell et al
7and Mauntel et
al.27However, these previous authors based group assign-
ment on the visual observation of medial knee displace-ment, whereas we classified groups based on NWB ankleDF-ROM. This suggests that the visual observation ofmedial knee displacement is associated with limited NWB
ankle DF-ROM; yet, limited ankle DF-ROM does not
necessarily result in altered movement patterns at the knee,such as medial knee displacement.Table 4. Jump-Landing Lower Extremity Kinematics for Groups Based on the Nonweight-Bearing–Position and Weight-Bearing–Lunge Assessments
DisplacementaAnkle-Dorsiflexion Range of Motion
Nonweight-Bearing Position Weight-Bearing Lunge
Mean 6SD (95% Confidence Interval)
Effect SizeMean 6SD (95% Confidence Interval)
Effect Size Normal (n ¼20) Limited (n ¼20) Normal (n ¼20) Limited (n ¼20)
Knee flexion 76.14 614.72 (69.59, 82.70) 74.38 614.23 (67.83, 80.93) 0.12 75.34 614.84 (68.40, 82.29) 75.18 614.16 (68.55, 81.81) 0.01
Knee valgus /C01.5462.48 (/C02.45,/C00.64) /C00.7761.37 (/C01.68, 0.14) 0.4 /C00.7361.14 (/C01.26, 0.20) /C01.5862.58 (/C02.80,/C00.37) 0.46
Knee varus 11.80 68.87 (8.18, 15.43) 12.99 67.03 (9.36, 16.62) 0.15 11.14 67.41 (7.67, 14.61) 13.65 68.42 (9.71, 17.59) 0.32
Knee external rotation /C03.7865.03 (/C05.74,/C01.81) /C01.7963.51 (/C03.75, 0.18) 0.47 /C02.2664.35 (/C04.30,/C00.23) /C03.3064.50 (/C05.41,/C01.20) 0.24
Knee internal rotation 15.70 615.83 (9.75, 21.65) 12.12 69.76 (6.17, 18.07) 0.28 16.82 614.49 (10.03, 23.60) 11.00 611.18 (5.77, 16.23) 0.45
Ankle dorsiflexion /C052.02 619.11 ( /C060.03, /C044.02) /C052.71 616.14 ( /C060.72, /C044.71) 0.04 /C050.24 619.63 ( /C059.42, /C041.05) /C054.50 615.20 ( /C061.62, /C047.39) 0.24
aKinematic sign convention: ț, knee flexion, knee varus, and knee internal rotation; /C0, knee valgus, knee external rotation, and ankle dorsiflexion.
Journal of Athletic Training 729

It is possible that other neuromuscular alterations, in
addition to limited NWB ankle DF-ROM, are present inindividuals with altered lower extremity movement pat-terns. Padua et al
28recently evaluated the neuromuscular
characteristics of the lower extremity muscles in the sameparticipants who demonstrated medial knee displacementduring the double-legged squat, which was eliminated witha 2-in (5.08-cm) heel lift.
7The medial-knee–displacement
group displayed significantly greater muscle activation ofthe hip adductor, gastrocnemius, and tibialis anteriormuscles in comparison with the control group. The heellift not only eliminated medial knee displacement but alsodecreased muscle activation during the descent phase of thesquat in the gastrocnemius and tibialis anterior muscles by32% and 55%, respectively. In a population displayingmedial knee displacement, increasing the tibial angle in theanterior direction with a heel lift was successful in
improving knee mechanics. However, hip-adductor muscle
activation, which contributes to medial knee displacement,was not altered with the heel lift. Knee kinematics areaffected by both proximal and distal influences. Ourparticipants had restricted ankle DF-ROM but not neces-sarily medial knee displacement. Therefore, it is likely theneuromuscular characteristics were different in the samplepopulations. The combination of altered muscle activa-tion
27,28and limited NWB ankle DF-ROM7,27may be
necessary to ultimately facilitate altered lower extremitykinematics.
Limited ankle DF during movement may facilitate
compensations at the foot and ankle joints but may notaffect the knee in some individuals. The participants in ourstudy had limited ankle DF but no history of lower
extremity surgery and no musculoskeletal injury in the
previous 6 months. Limited motion in healthy, physicallyactive individuals can be due to a variety of factors,including soft tissue tightness (gastrocnemius, soleus,Achilles tendon), osteokinematic restrictions of the bonesand joints (flexion-extension), arthrokinematic restrictions(roll, glide, spin), or even frequently wearing high-heeledshoes, among others. Previous researchers
29,30have sug-
gested that limited ankle DF contributes to excessive rear-foot pronation, calcaneal eversion, and talar-head adductionand plantar flexion. Essentially, because of limited sagittal-plane motion, the foot moves more in the frontal plane toachieve stability and successful movement. Talar-headmovement during pronation may cause internal rotation ofthe tibia and medial displacement at the knee. However, itis possible that not all individuals with ankle DF-ROMrestrictions compensate in that manner. We did not quantifyfoot kinematics, so we can only speculate.
In contrast to NWB measures, ankle DF-ROM assessed
during the WBL differentiated lower extremity kinematicsbetween the normal and limited groups. Individuals whoseWBL ankle DF-ROM was limited displayed less sagittal-plane displacement at the knee and ankle during thesquatting tasks as well as smaller peak knee-flexion angles.We consider those differences in knee and ankle displace-ments to be large and clinically meaningful because theassociated effect sizes ranged from 1.31 to 1.86 (Tables 2and 3). Our findings are consistent with those of Macrum etal,
13who noted that altering the ankle DF starting position
resulted in reduced knee-flexion displacement during adouble-legged squat. Macrum et al
13placed a 12 8wedgeunder the participant’s forefoot to position the ankle in
greater DF and ultimately reduce the available amount of
DF motion (restricted ankle DF) during a double-leggedsquat task. That resulted in decreased peak knee flexion andoverall knee-flexion displacement compared with perform-ing the double-legged squat without a forefoot wedge inplace (ie, unrestricted ankle DF). Additionally, Hoch andMcKeon
31reported that the WBL ankle DF-ROM predicted
anterior-reach distance during the Star Excursion BalanceTest ( R
2¼0.28). Single-legged squat depth, which is
largely influenced by knee-flexion displacement, is a key
factor contributing to the anterior-reach distance during theStar Excursion Balance Test. Thus, these combinedfindings demonstrate the importance of WBL ankle DF-ROM as a factor influencing knee-flexion displacement.
Frontal-plane knee motion was also different in those
with limited ankle DF-ROM during the WBL. Specifically,
those with greater ankle DF-ROM during the WBLdemonstrated increased knee-varus displacement duringthe SLS. This observation is in agreement with the resultsof Sigward et al,
14who reported a significant association
between greater frontal-plane knee valgus motion andlesser DF-ROM.
These findings may provide insight for ACL injury and
injury-prevention strategies given the alterations in sagittal-plane displacements (decreased knee flexion) in those withlimited ankle DF-ROM during the WBL and frontal-planeknee motion (increased knee varus) in those with greaterDF-ROM during the WBL. Video analyses have repeatedlyshown the body to be in an erect posture (decreased knee
flexion) when noncontact ACL injuries occur.
32,33De-
creased knee flexion may also be important, given how itinfluences ACL loading: less knee flexion results in a largerpatellar tendon–tibial shaft angle, thus producing greateranterior tibial shear force during quadriceps contrac-tion.
34,35In addition, the ability of the hamstrings to offset
anterior tibial shear forces and reduce ACL loading isreduced in positions of less knee flexion.
35Increased knee-
valgus motion and loading are also associated with a higher
risk of ACL injury and are observed during ACL injury
mechanisms.33,36,37Individuals with greater ankle DF-ROM
during the WBL did not demonstrate knee-valgus motionbut, rather, displayed greater knee-varus displacement thanthose with limited ankle DF-ROM during the WBL. Thus,interventions aimed at increasing ankle DF-ROM duringthe WBL may facilitate increased knee-flexion and -varusdisplacements and help minimize anterior shear force andknee-valgus–related ACL loading, respectively.
Limitations
Previous researchers have shown that participants who
demonstrate medial knee displacement during an OHS7and
medial knee excursion during a drop landing14also have
less ankle DF ROM assessed in NWB with 30 8of knee
flexion. One potential limitation of our study is that weevaluated and categorized individuals based on an NWBassessment with the knee in full extension. However, wealso measured ankle DF-ROM with the knee flexed duringour data-collection session (normal, 22.27 86 4.498;
limited, 8.52 86 3.768). We performed a Pearson product
moment correlation coefficient analysis among the 3assessments (knee flexed, knee extended, WBL) and found
730 Volume 49 /C15Number 6 /C15December 2014

a strong association between both NWB measures ( r¼
0.919; P,.001). This indicates that our kinematic results
would have been similar had we grouped participants basedon an NWB measure with the knee flexed. We alsocalculated the 50th percentile cutoff point (16 8) in the same
manner as we did for the WBL test and noted similar groupmeans (normal, 22.30 64.45; limited, 8.48 63.69). One
participant switched from the limited group to the normalgroup, and 1 participant switched from the normal group to
the limited group. Therefore, we feel confident that the
kinematic data would be the same as our current resultsregardless of grouping participants using the NWB measurewith the knee extended or flexed.
Inherent differences exist in the measurement techniques
for the 2 DF-ROM assessments used in this study. Often,
when clinicians measure ankle DF-ROM in an NWBposition, they maintain the subtalar joint in neutral positionto confirm they are measuring true DF at the talocruraljoint. However, the WBL is typically performed efficientlyin the clinic without controlling subtalar position. Thepotential benefit of this assessment is that it better evaluatesfunctional movement of the entire foot and ankle complex.We do not control for subtalar-joint position during
movement-screening sessions using the OHS, SLS, and
JL, so we felt comfortable performing the WBL assessmentin this manner. The amounts of available motion duringthese 2 assessments are very different, with greater motionachieved when subtalar position is not controlled. Althoughthis may be a potential limitation of this study, we did notdirectly compare the 2 measures; therefore, we do not feelthis is a limitation of our findings.
Peak joint angles were identified during the descent phase
of each task. However, we do know when, during thedescent phase of each task, the peak angle occurred. We areunsure whether the peak knee-flexion angle occurredsimultaneously with the peak ankle-DF angle. The various
timings of peak angles may have an influence on injury.
Finally, we were not blinded to the participants’ group
assignment, which may have caused unintentional biasduring ROM measurements. Yet the measurement tech-niques were standardized with good reliability. Our results
are generalizable only to healthy, college-aged individuals.
Therefore, whether results would be similar in an injuredpopulation is unclear. Additionally, we did not assessmuscle activation or muscle strength as variables in thisstudy, but it would be beneficial to investigate them in thefuture.
Recommendations for Future Research
Future researchers should continue to investigate the
influence of ankle DF-ROM on lower extremity kinematics.
Intervention studies would be beneficial to determinewhether altering ankle DF ROM, through addressing softtissue or arthrokinematic restrictions, results in alteredlower extremity kinematics in a way that is beneficial forrehabilitation and injury prevention.
CONCLUSIONS
Our results suggest that ankle DF-ROM during the WBL
may be a more sensitive measure for identifying those at
risk for high-risk movement patterns compared with NWBpassive-ankle DF-ROM measures. Ankle DF-ROM isreported to be restricted in physically active individuals
and after lower extremity injury; however, those measure-ments typically use passive NWB measurements.
38Al-
though those passive measurements remain important, our
findings suggest that including the WBL in the assessment
of ankle DF-ROM is also important and may better identify
those at risk for dysfunctional movement patterns during
functional tasks.
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Address correspondence to Rebecca L. Begalle, PhD, ATC, School of Kinesiology and Recreation, Illinois State University, 251F
McCormick Hall, Campus Box 5120, Normal, IL 61790. Address e-mail to rbegall@ilstu.edu .
732 Volume 49 /C15Number 6 /C15December 2014