Validity and inter-rater reliability of

ankle motion observed during a single

leg squat
Paloma Guillén-Rogel1 ,2 , Cristina San Emeterio1 ,2 and Pedro J. Marín3
1
Institute of Biomedicine (IBIOMED), León University, León, Spain
2
Faculty of Health Sciences, Miguel de Cervantes European University, Valladolid, Spain
3
CYMO Research Institute, Valladolid, Spain

ABSTRACT
Background. The single leg squat (SLS) test is a clinical functional test commonly used
to evaluate clinically aberrant movement patterns of the knee. The SLS could be an
interesting option to analyze ankle control in the frontal plane during dynamic load
analysis. However, to date, there are no studies that have analyzed the associations
between the increased subtalar joint pronation by navicular drop (ND) test and ankle
control with single leg squat (SLSankle ) using a three-point scale. The purpose of this
study was to evaluate the reliability of a clinical observation method to assess and
determine the relationship between navicular drop (ND) and ankle control on the
SLSankle score.
Methods. A total of fifty-five healthy, physically active (31 females and 24 males)
volunteers participated in this study. The degree of subtalar pronation was assessed
through the ND test, and the ankle control was defined as the ankle displacement in
the frontal plane during the SLS.
Results. We found good intra-rater and inter-rater agreement during SLSankle , with
Kappa values from 0.731 to 0.750. The relationship between the SLSankle and ND was
significant ; the Spearman’s rank correlation coefficient was 0.504 (p < 0.05).
Conclusions. The SLSankle score supplied the clinical practice with a reliable and valid
alternative for quantifying foot mobility in comparison to the ND test.
Submitted 10 December 2021
Accepted 2 February 2022
Subjects Biomechanics, Sports Injury, Sports Medicine
Published 15 February 2022
Keywords Navicular drop, Navicular motion, Foot kinematics, Pronation, Visual assessment,
Corresponding author Medial longitudinal arch
Pedro J. Marín, pjmarin@cymori.com
Academic editor
Emiliano Cè INTRODUCTION
Additional Information and The single leg squat (SLS) test is a clinical functional test commonly used to evaluate
Declarations can be found on
page 8
movement patterns of the lower limbs to assist clinicians with screening and diagnosis
(Weeks, Carty & Horan, 2012). Visual observation movement screening tests offer an
DOI 10.7717/peerj.12990
inexpensive, readily accessible, and easily applied assessment of the movement system in a
Copyright clinical setting.
2022 Guillén-Rogel et al.
The SLS test is a tool to assess the risk of lower extremity injury (Ugalde et al., 2015),
Distributed under such as anterior cruciate ligament (ACL) injury (Yamazaki et al., 2010; Yokoyama et al.,
Creative Commons CC-BY 4.0
2021), patellofemoral pain (Herrington, 2014; Gwynne & Curran, 2018), and non-arthritic
OPEN ACCESS hip pain (McGovern et al., 2020).

How to cite this article Guillén-Rogel P, San Emeterio C, Marín PJ. 2022. Validity and inter-rater reliability of ankle motion observed
during a single leg squat. PeerJ 10:e12990 http://doi.org/10.7717/peerj.12990
 The movement patterns are used with visual rating scales (Harris-Hayes et al., 2014).
The observer assesses the degree of medial–lateral knee motion during a single limb squat.
Often, medial knee motion during the squat is indicative of hip abductor and/or external
rotation muscle dysfunction (Ageberg et al., 2010; Crossley et al., 2011). Foot and ankle
movement and mechanics, along with the hip musculature, may also have an impact on
the kinematics of the lower extremity.
During closed-chain activities, restricted ankle dorsiflexion (DF) range of motion (ROM)
is often accompanied by decreased sagittal plane motion of the knee, hip, and trunk, as well
as increased frontal plane motion of the lower extremity (Bell, Padua & Clark, 2008). For
example, during a squat, restricted DF ROM may result in excessive subtalar joint pronation
and midtarsal dorsiflexion (Fong et al., 2011) tibial and femoral internal rotation, medial
knee displacement, knee valgus (Macrum et al., 2012; Dill et al., 2014) and pelvis drop
(Wilczyński, Zorena & Ślęzak, 2020). Decreased DF ROM was also associated with reduced
quadriceps activation and increased soleus activity during the descent portion of a squat
(Macrum et al., 2012). Thus, the ankle is important for evaluation during the single leg
squat and plays as it has a stabilizing performance during the closed chain task (Warner et
al., 2019).
The navicular drop (ND) test described by Brody (1982) is a clinical test used to evaluate
rearfoot and midfoot pronation and assess the function of the medial longitudinal arch.
The integrity of the medial longitudinal arch (MLA) is an important factor in kinematics
and function of the lower extremities during weight bearing (Nilsson et al., 2012).
ND is measured by recording the difference (in millimeters) between navicular tuberosity
height in standing weight bearing and resting standing foot position (Shrader et al., 2005).
Firstly, the subject was the sitting position with both knees in 90◦ flexion, with the foot on
the floor and then the navicular tuberosity was palpated and market. Clinical measures the
distance from the navicular tuberosity to the floor. Secondly, the participant standing with
weight equally distributed on both feet, clinician measures distance from the navicular
tuberosity to the floor (Brody, 1982; Mulligan & Cook, 2013; Elataar et al., 2020; Allam et
al., 2021).
The navicular drop test demonstrates excellent reliability, with intra-rater and inter-rater
interclass correlation coefficient values ranging from 0.914 to 0.945 (Spörndly-Nees et al.,
2011; Zuil-Escobar et al., 2018). An ND ≥ 10 mm is considered an excessive amount of foot
pronation (Headlee et al., 2008). Furthermore, excessive pronation of the foot has been
associated with increased risk of lower extremity injuries in military cadets (Levy et al.,
2006) and athletes (Michelson, Durant & McFarland, 2002).
In contrast, dynamic weight-bearing task analysis is very important to reproduce
activities of daily living. The SLS could be an interesting option to analyze ankle control in
the frontal plane during dynamic load analysis. However, to date, there are no studies that
have analyzed the associations between the increased subtalar joint pronation by ND test
and ankle control with single leg squat (SLSankle ) using a three-point scale.
Therefore, the aims of this study were to (1) evaluate the reliability of a clinical
observation method of assessment, and (2) determine the relation between the assessment

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 2/13

 of ankle control during SLSankle and the navicular test. We hypothesized that a higher ND
score would correlate with the lateral malleolus displacement during the SLS.

MATERIALS & METHODS

An a priori power analysis was conducted to estimate the sample size. G*Power software
(G*Power 3.1.9.6 Kiel University, Kiel, Germany) (Faul et al., 2007) estimated a sample
size of 34 subjects (significance level = 0.05; required power = 0.80; correlation among
repeated measures = 0.30). A pilot study with 6 subject was used to estimate the sample
size.

Study design
An observational study was performed between April and June 2019. The study was
conducted according to the guidelines of the Declaration of Helsinki and approved by
the CyMO Research Institute (Valladolid, Spain: 1.200.553). All the participants read and
signed an approved, written informed consent document before data collection.

Participants
Overall, fifty-five healthy, physically active adult volunteers, 31 females (21.3 ± 5.7
yrs., 163.5 ± 7.4 cm, 59.7 ± 7.7 kg) and 24 males (27.4 ± 12.7 yrs., 177.6 ± 7.9 cm,
76.8 ± 10.3 kg), were recruited for this study. All participants were healthy, reporting
no injuries. Participants were excluded if they had any joint pathology in the hip, knee,
or ankle that caused pain or restricted movement, neuromuscular disease, recent heel or
knee pain, or a history of recent lower extremity trauma or elective surgery in the last six
months.

Procedures & measurements

Participants completed three laboratory sessions in this study (one familiarization session
and two test sessions) at one-week intervals. All sessions were performed at the same time of
day to minimize the effect of circadian rhythms. All participants were instructed to refrain
from exercising for 48 h prior to testing to reduce the potential influence of post-exercise
muscle soreness or fatigue on performance in the SLSankle test. During the testing session,
participants carried out the following tests in a randomized order: the ND test and the
SLSankle test.

Navicular drop
Each subject was asked to stand barefoot, with weight distributed evenly over each foot.
The navicular tuberosity was palpated and marked with a washable marker. With the
subtalar joint in the neutral position, the distance between the navicular tuberosity and the
floor was measured, in millimeters, with a caliper (Mulligan & Cook, 2013; Okamura et al.,
2021).
The procedure was repeated three times for each participant. One measurement is
subtracted from the other. In the cases in which this difference, expressed in millimeters,
is ≥10 mm, the ND signifies an excessive pronation of the foot (Brody, 1982; Cote et al.,
2005).

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 3/13

 Figure 1 SLSankle score. (A) ‘‘0’’ point; (B) ‘‘1’’ point; (C) ‘‘2’’ points.
Full-size DOI: 10.7717/peerj.12990/fig-1

Single leg squat

The SLS was evaluated with the Leg MOtion R system (Leg Motion R , Check your Motion,
Albacete, Spain) in a weight-bearing position. The Leg Motion R system (Check your
Motion R , Albacete, Spain) is a valid portable, and easy to use alternative to the weight-
bearing lunge test to assess ankle dorsiflexion ROM in healthy participants (Calatayud et al.,
2015; Romero Morales et al., 2017; Moreno-Pérez et al., 2020). A digital camera (FDR-AX33,
Sony, Tokyo, Japan) registered, through video recording, the lateral displacement of the
ankle. The camera was placed on a tripod 3 m in front of the participant, at a height of
approximately 0.9 m from the ground. This height was aligned approximately to the level of
the participants’ pelvis. Video recording were made at 50 frames per second at a resolution
of 1,920 × 1,080 pixels.
Participants stood barefoot with their feet shoulder-width apart, hips and knees extended,
toes facing forward, and equal weight on both feet, and a marking strip made of masking
tape (a rectangle with measures 30 × 10 millimeters) were applied to the skin over the
lateral malleolus (Fig. 1).
Participants then placed one foot on the Leg MOtion platform with the second toe
close to a corresponding starting line. Frontal plane ankle control was evaluated by visual
observation (Junge et al., 2012) with a metal stick. A metal stick was placed along the line
of the 2nd toe to indicate movement in the frontal plane during the SLSankle . Ankle control
was defined as the ankle displacement in the frontal plane during the SLSankle .
Participants performed a SLS as far down as comfortably possible in four seconds
(Nakagawa et al., 2012), keeping their trunk upright, their arms out to the side, and flexing
their knee to at least 60◦ (Wyndow et al., 2016; Guillén-Rogel et al., 2021). In a previous
study there are a consensus about the depth of the squat that a must be performed to at
least 60◦ of knee flexion to be clinically rated as good (Crossley et al., 2011). Adequate knee
flexion was visually confirmed by a researcher (Schmidt, Harris-Hayes & Salsich, 2019).
Prior to testing, a researcher provided a visual demonstration of the test. Participants

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 4/13

 performed 10 practice trials with each limb to become comfortable with the task. After a
3-minute rest, each participant performed five repetitions of the SLSankle test with each
lower extremity, which was videotaped.
After a 15-day wash-out period (Streiner & Norman, 2008), two examiners (a
physiotherapist and an athletic trainer) were sent the video recordings to assess the
motion and rate the degree of ankle control. The examiners were trained to observe each
video no more than two times without any pausing or slow motion, and each had more
than 10 years of video-analysis experience. The sequence of the recording was randomized
with a web-based research randomizer to minimize bias (Urbaniak & Plous, 2007).
Ankle control was scored using a three-point scale (0—good ankle control, 1—reduced
and 2—poor) based on the distance from the metal stick to the lateral malleolus during
the SLS movement (Fig. 1). A score of 0 was recorded when raters observed that the
distance between the lateral malleolus and the metal stick was unchanged from the single
leg standing to squatting position. A score of 1 was given when the raters observed that the
distance from the lateral malleolus to the metal stick decreased from the single leg standing
to squat position. A score of 2 was recorded when the marker on the lateral malleolus was
aligned with the metal stick. The subjects were rated by their poorest test performance
among the five trials.

Statistical analysis
Cohen’s kappa test was used to determine the intra-rater and inter-rater reliabilities. The
kappa values were defined as poor if kappa was 0.20, fair for values of 0.21 to 0.40, moderate
for 0.41 to 0.60, good for 0.61 to 0.80, and very good for 0.81 to 1.00 (Ashby, 1991).
One-way analysis of variance (ANOVA) was used to compare the ND test scores among
the ankle control groups (good, reduced, or poor).
Spearman’s rank correlation coefficient was used to determine the correlation between
the subjective assessment of ankle control with the scale of ‘‘good’’, ‘‘reduced’’, or ‘‘poor’’
and the ND test. All statistical analyses were conducted using SPSS (Version 22.0, IBM,
Armonk, NY, USA). Effect sizes (d) were analyzed to determine the magnitude of an effect
independent of sample size (the difference between the means divided by the pooled SD).
A score of 0.5 and below was considered a low d, 0.51–0.8 considered a medium d, and 0.81
and above a large d (Cohen, 2013). Statistical significance was established at p < 0.05.

RESULTS
Intra-rater reliability for the ankle control assessment
We found good agreement between the first and second test during SLSankle , with kappa
values of 0.750 for the right side and 0.731 for the left side.

Inter-rater reliability for the ankle control assessment

The kappa values for the agreement between raters were 0.744 for the right side and 0.732
for the left side.
ANOVA showed significant differences (p < 0.05) for the ND test among the all SLSankle
scores (Fig. 2).

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 5/13

 Figure 2 SLSankle and ND test. *Significantly different to good and poor SLSankle score (p < 0.05). **Sig-
nificantly different to good and reduced SLSankle score (p < 0.05).
Full-size DOI: 10.7717/peerj.12990/fig-2

Additionally, the relationship between the ankle control during SLSankle and ND tests
were investigated using the Spearman’s rho correlation. The Spearman’s rank correlation
coefficient was 0.504 (p < 0.05).

DISCUSSION
The aim of this study was to evaluate the reliability of a clinical observation method to
assess and determine the relationship between navicular drop (ND) and ankle control
on the single leg squat ankle score (SLSankle ). We found good intra-rater and inter-rater
agreement during SLSankle . The results determined that a higher ND score was correlated
with lateral malleolus displacement during the SLS.
This study compared the reliability of a physiotherapy rater and athletic trainer rater;
therefore, the experience level of these examiners is more likely to be an indicator of
reliability (Weeks, Carty & Horan, 2012). Nevertheless, Tate et al. (2015) indicate excellent
expert and novice test–retest reliability in measuring the frontal plane knee alignment
during SLS.
Two-dimensional measurements of a lower extremity during a SLS, such as the frontal
plane projection angle and visual evaluation, is suggested to be more cost effective and
can easily be conducted in clinical settings as an alternative to three-dimensional motion
capture (Hansen, Lundgaard-Nielsen & Henriksen, 2021). We found good intra- and inter-
rater agreement for SLSankle score. Similarly, Stensrud et al. (2011) conducted an assessment

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 6/13

 using a two-dimensional video analysis during SLS in healthy participants and established
excellent inter-rater reliability.
Various scoring systems have been used to assess dynamic alignment in the literature.
Ressman, Grooten & Rasmussen Barr (2019) found that the analysis scales with a ≤ three-
point rating scale show a higher inter-rater reliability compared with ≥ four-point rating
scales of visual assessment of movement in the SLS test. However, there are no previous
studies that have analyzed ankle control during a SLS using a three-point scale. The SLSankle
score shows the visual assessment scores of good, reduced, and poor on a three-point scale.
However, Perrott et al. (2012) conducted analysis of foot alignment with a two-point scale
(good and poor). The primary differences between the current study and Perrott et al.
(2012) and Perrott et al. (2021) were not related to the degree of pronation.
Foot pronation was described a predictor of altered joint kinetics and injuries (Brund et
al., 2017), such as medial stress syndrome (Hamstra-Wright, Bliven & Bay, 2015; Menéndez
et al., 2020). In addition, the alteration of the MLA can influence the biomechanics of
the lower extremities. Therefore, from an injury prevention perspective, it is important
to assess the deficits in active foot stabilization during dynamic pronation (Tourillon,
Gojanovic & Fourchet, 2019).
The clinical implications of the test resemble the conditions of daily life, require no
expensive or advanced equipment, and the experienced examiners can conduct a reliable
visual assessment of the frontal plane of the ankle during an SLS test. Therefore, the use of
SLSankle score is a simple screening tool that can reduce the need for health practitioners to
conduct another test of pronation.
A clear strength of the test used in this study is that it is easy to use and quickly performed,
which gives it strength as a clinical test where both time and reliable evaluation are essential
for diagnostics. The SLS test can allow us to simultaneously make an overall assessment of
the motor control of the ankle, knee, hip, and trunk. The Leg Motion R system provides a
standardized device to perform the foot position during the SLSankle . On the other hand,
it should be noted that it may also be valid to conduct the evaluation using the malleoli
instead of the navicular bone as a landmark (Kanai et al., 2020).
There are some limitations of the current study. Only healthy individuals were included,
while participants with plantar heel pain or joint pathology in the hip, knee, or ankle
that caused pain were excluded. Contrastingly, despite the potential benefits of using
the ND test, another limitation of the study is the ND test only capable of measuring
displacement in the sagittal plane, while the movement of the navicular takes place in all
three planes simultaneously (Vinicombe, Raspovic & Menz, 2001). Therefore, the evaluation
of pronation movement was conducted without three-dimensional analyses; however, we
aimed exclusively at assessing the reliability of the test assessments.

CONCLUSIONS
The findings of this study reveal that ankle displacement is a reliable tool to assess a single
leg squat. A poor rating on the SLS test is associated with higher pronation in the ND test.
The SLSankle score has demonstrated good inter-rater and intra-rater reliability for
two examiners. Therefore, the ankle assessment should be considered during dynamic

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 7/13

 assessment and supplies clinical practice with a valid alternative to quantify foot mobility
in comparison to the ND test.

ACKNOWLEDGEMENTS
The authors wish to thank the participants of this study for their cooperation.

ADDITIONAL INFORMATION AND DECLARATIONS

Funding
The authors received no funding for this work.

Competing Interests
We have conflicts of interest to disclose. Pedro J. Marín patented the LegMotion R system
(CheckyourMOtion R , Albacete, Spain).

Author Contributions
• Paloma Guillén-Rogel and Cristina San Emeterio conceived and designed the
experiments, performed the experiments, analyzed the data, authored or reviewed
drafts of the paper, and approved the final draft.
• Pedro J. Marín conceived and designed the experiments, performed the experiments,
analyzed the data, prepared figures and/or tables, authored or reviewed drafts of the
paper, and approved the final draft.

Human Ethics
The following information was supplied relating to ethical approvals (i.e., approving body
and any reference numbers):
CyMO Research Institute.

Patent Disclosures
The following patent dependencies were disclosed by the authors:
Leg Motion R , Check your Motion, Albacete, Spain.

Data Availability
The following information was supplied regarding data availability:
The raw measurements are available in the Supplementary File.

Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.12990#supplemental-information.

REFERENCES
Ageberg E, Bennell KL, Hunt MA, Simic M, Roos EM, Creaby MW. 2010. Validity and
inter-rater reliability of medio-lateral knee motion observed during a single-limb
mini squat. BMC Musculoskeletal Disorders 11:265
DOI 10.1186/1471-2474-11-265.

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 8/13

 Allam HH, Muhsen A, Al-walah MA, Alotaibi AN, Alotaibi SS, Elsayyad LK. 2021.
Effects of plyometric exercises versus flatfoot corrective exercises on postural control
and foot posture in obese children with a flexible flatfoot. Applied Bionics and
Biomechanics 2021:Article 3635660 DOI 10.1155/2021/3635660.
Ashby D. 1991. Practical statistics for medical research. Douglas G. Altman, Chapman
and Hall, London. Statistics in Medicine 10:1635–1636
DOI 10.1002/sim.4780101015.
Bell DR, Padua DA, Clark MA. 2008. Muscle strength and flexibility characteristics of
people displaying excessive medial knee displacement. Archives of Physical Medicine
and Rehabilitation 89:1323–1328 DOI 10.1016/j.apmr.2007.11.048.
Brody DM. 1982. Techniques in the evaluation and treatment of the injured runner. The
Orthopedic Clinics of North America 13:541–558
DOI 10.1016/S0030-5898(20)30252-2.
Brund RBK, Rasmussen S, Nielsen RO, Kersting UG, Laessoe U, Voigt M. 2017. Medial
shoe-ground pressure and specific running injuries: a 1-year prospective cohort
study. Journal of Science and Medicine in Sport 20:830–834
DOI 10.1016/j.jsams.2017.04.001.
Calatayud J, Martin F, Gargallo P, García-Redondo J, Colado JC, Marín PJ. 2015. The
validity and reliability of a new instrumented device for measuring ankle dorsiflexion
range of motion. International Journal of Sports Physical Therapy 10:197–202.
Cohen J. 2013. Statistical power analysis for the behavioral sciences. New York: Routledge
DOI 10.4324/9780203771587.
Cote KP, Brunet ME, Gansneder BM, Shultz SJ. 2005. Effects of pronated and supinated
foot postures on static and dynamic postural stability. Journal of Athletic Training
40:41–46.
Crossley KM, Zhang W-J, Schache AG, Bryant A, Cowan SM. 2011. Performance on the
single-leg squat task indicates hip abductor muscle function. The American Journal of
Sports Medicine 39:866–873 DOI 10.1177/0363546510395456.
Dill KE, Begalle RL, Frank BS, Zinder SM, Padua DA. 2014. Altered knee and an-
kle kinematics during squatting in those with limited weight-bearing–lunge
ankle-dorsiflexion range of motion. Journal of Athletic Training 49:723–732
DOI 10.4085/1062-6050-49.3.29.
Elataar FF, Abdelmajeed SF, Abdellatif NMN, Mohammed MM. 2020. Core muscles’
endurance in flexible flatfeet: a cross-sectional study. Journal of Musculoskeletal &
Neuronal Interactions 20:404–410.
Faul F, Erdfelder E, Lang A-G, Buchner A. 2007. G*Power 3: a flexible statistical power
analysis program for the social, behavioral, and biomedical sciences. Behavior
Research Methods 39:175–191 DOI 10.3758/BF03193146.
Fong C-M, Blackburn JT, Norcross MF, McGrath M, Padua DA. 2011. Ankle-
dorsiflexion range of motion and landing biomechanics. Journal of Athletic Training
46:5–10 DOI 10.4085/1062-6050-46.1.5.
Guillén-Rogel P, Barbado D, Franco-Escudero C, San Emeterio C, Marín PJ. 2021.
Are core stability tests related to single leg squat performance in active females?

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 9/13

 International Journal of Environmental Research and Public Health 18:5548
DOI 10.3390/ijerph18115548.
Gwynne CR, Curran SA. 2018. Two-dimensional frontal plane projection angle can
identify subgroups of patellofemoral pain patients who demonstrate dynamic knee
valgus. Clinical Biomechanics 58:44–48 DOI 10.1016/j.clinbiomech.2018.06.021.
Hamstra-Wright KL, Bliven KCH, Bay C. 2015. Risk factors for medial tibial stress
syndrome in physically active individuals such as runners and military personnel: a
systematic review and meta-analysis. British Journal of Sports Medicine 49:362–369
DOI 10.1136/bjsports-2014-093462.
Hansen R, Lundgaard-Nielsen M, Henriksen M. 2021. Visual assessment of dynamic
knee joint alignment in patients with patellofemoral pain: an agreement study. PeerJ
9:e12203 DOI 10.7717/peerj.12203.
Harris-Hayes M, Steger-May K, Koh C, Royer NK, Graci V, Salsich GB. 2014. Classifica-
tion of lower extremity movement patterns based on visual assessment: reliability
and correlation with 2-dimensional video analysis. Journal of Athletic Training
49:304–310 DOI 10.4085/1062-6050-49.2.21.
Headlee DL, Leonard JL, Hart JM, Ingersoll CD, Hertel J. 2008. Fatigue of the plantar
intrinsic foot muscles increases navicular drop. Journal of Electromyography and
Kinesiology 18:420–425 DOI 10.1016/j.jelekin.2006.11.004.
Herrington L. 2014. Knee valgus angle during single leg squat and landing in
patellofemoral pain patients and controls. The Knee 21:514–517
DOI 10.1016/j.knee.2013.11.011.
Junge T, Balsnes S, Runge L, Juul-Kristensen B, Wedderkopp N. 2012. Single leg mini
squat: an inter-tester reproducibility study of children in the age of 9–10 and 12–
14 years presented by various methods of kappa calculation. BMC Musculoskeletal
Disorders 13:203 DOI 10.1186/1471-2474-13-203.
Kanai Y, Mutsuzaki H, Watanabe M, Takeuchi R, Mataki Y, Endo Y, Yozu A. 2020. Use
of malleoli as an indicator for flatfoot in patients with Down syndrome: development
of a simple and non-invasive evaluation method through medial longitudinal arch.
Journal of Physical Therapy Science 32:315–318 DOI 10.1589/jpts.32.315.
Levy JC, Mizel MS, Wilson LS, Fox W, McHale K, Taylor DC, Temple HT. 2006.
Incidence of foot and ankle injuries in west point cadets with pes planus com-
pared to the general cadet population. Foot & Ankle International 27:1060–1064
DOI 10.1177/107110070602701211.
Macrum E, Bell DR, Boling M, Lewek M, Padua D. 2012. Effect of limiting ankle-
dorsiflexion range of motion on lower extremity kinematics and muscle-
activation patterns during a squat. Journal of Sport Rehabilitation 21:144–150
DOI 10.1123/jsr.21.2.144.
McGovern RP, Martin RL, Phelps AL, Kivlan BR, Nickel B, Christoforetti JJ. 2020.
Conservative management acutely improves functional movement and clinical
outcomes in patients with pre-arthritic hip pain. Journal of Hip Preservation Surgery
7:95–102 DOI 10.1093/jhps/hnz075.

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 10/13

 Menéndez C, Batalla L, Prieto A, MÁ Rodríguez, Crespo I, Olmedillas H. 2020.
Medial tibial stress syndrome in novice and recreational runners: a systematic
review. International Journal of Environmental Research and Public Health 17:7457
DOI 10.3390/ijerph17207457.
Michelson JD, Durant DM, McFarland E. 2002. The injury risk associated with pes
planus in athletes. Foot & Ankle International 23:629–633
DOI 10.1177/107110070202300708.
Moreno-Pérez V, Del Coso J, Raya-González J, Nakamura FY, Castillo D. 2020. Effects
of basketball match-play on ankle dorsiflexion range of motion and vertical jump
performance in semi-professional players. The Journal of Sports Medicine and Physical
Fitness 60(1):110–118 DOI 10.23736/S0022-4707.19.09918-3.
Mulligan EP, Cook PG. 2013. Effect of plantar intrinsic muscle training on medial
longitudinal arch morphology and dynamic function. Manual Therapy 18:425–430
DOI 10.1016/j.math.2013.02.007.
Nakagawa TH, Moriya ET, Maciel CD, Serrão FV. 2012. Trunk, pelvis, hip, and knee
kinematics, hip strength, and gluteal muscle activation during a single-leg squat
in males and females with and without patellofemoral pain syndrome. Journal of
Orthopaedic & Sports Physical Therapy 42:491–501
DOI 10.2519/jospt.2012.3987.
Nilsson MK, Friis R, Michaelsen MS, Jakobsen PA, Nielsen RO. 2012. Classification of
the height and flexibility of the medial longitudinal arch of the foot. Journal of Foot
and Ankle Research 5:3 DOI 10.1186/1757-1146-5-3.
Okamura K, Egawa K, Ikeda T, Fukuda K, Kanai S. 2021. Relationship between
foot muscle morphology and severity of pronated foot deformity and foot
kinematics during gait: a preliminary study. Gait & Posture 86:273–277
DOI 10.1016/j.gaitpost.2021.03.034.
Perrott MA, Pizzari T, Opar M, Cook J. 2012. Development of clinical rating criteria
for tests of lumbopelvic stability. Rehabilitation Research and Practice 2012:1–7
DOI 10.1155/2012/803637.
Perrott MA, Pizzari T, Opar MS, Cook J. 2021. Athletes with a clinical rating of
good and poor lumbopelvic stability have different kinematic variables during
single leg squat and dip test. Physiotherapy Theory and Practice 37:906–915
DOI 10.1080/09593985.2019.1655823.
Ressman J, Grooten WJA, Rasmussen Barr E. 2019. Visual assessment of move-
ment quality in the single leg squat test: a review and meta-analysis of inter-
rater and intrarater reliability. BMJ Open Sport & Exercise Medicine 5:e000541
DOI 10.1136/bmjsem-2019-000541.
Romero Morales C, Calvo Lobo C, Rodríguez Sanz D, Sanz Corbalán I, Ruiz Ruiz BB,
López López D. 2017. The concurrent validity and reliability of the Leg Motion
system for measuring ankle dorsiflexion range of motion in older adults. PeerJ
5:e2820 DOI 10.7717/peerj.2820.
Schmidt E, Harris-Hayes M, Salsich GB. 2019. Dynamic knee valgus kinematics
and their relationship to pain in women with patellofemoral pain compared to

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 11/13

 women with chronic hip joint pain. Journal of Sport and Health Science 8:486–493
DOI 10.1016/j.jshs.2017.08.001.
Shrader JA, Popovich JM, Gracey GC, Danoff JV. 2005. Navicular drop measurement
in people with rheumatoid arthritis: interrater and intrarater reliability. Physical
Therapy 85:656–664 DOI 10.1093/ptj/85.7.656.
Spörndly-Nees S, Dåsberg B, Nielsen RO, Boesen MI, Langberg H. 2011. The navicular
position test—a reliable measure of the navicular bone position during rest and
loading. International Journal of Sports Physical Therapy 6:199–205.
Stensrud S, Myklebust G, Kristianslund E, Bahr R, Krosshaug T. 2011. Correlation
between two-dimensional video analysis and subjective assessment in evaluating
knee control among elite female team handball players. British Journal of Sports
Medicine 45:589–595 DOI 10.1136/bjsm.2010.078287.
Streiner DL, Norman GR. 2008. Biases in responding. In: Health measurement scales.
Oxford: Oxford University Press, 103–134
DOI 10.1093/acprof:oso/9780199231881.003.0006.
Tate J, True H, Dale B, Baker C. 2015. Expert versus novice interrater and intrarater
reliability of the frontal plane projection angle during a single-leg squat. International
Journal of Athletic Therapy and Training 20:23–27 DOI 10.1123/ijatt.2014-0116.
Tourillon R, Gojanovic B, Fourchet F. 2019. How to evaluate and improve foot
strength in athletes: an update. Frontiers in Sports and Active Living 1:46
DOI 10.3389/fspor.2019.00046.
Ugalde V, Brockman C, Bailowitz Z, Pollard CD. 2015. Single leg squat test and its
relationship to dynamic knee valgus and injury risk screening. PM & R 7:229–235
DOI 10.1016/j.pmrj.2014.08.361.
Urbaniak GC, Plous S. 2007. Research randomizer (version 4.0) [computer software].
Vinicombe A, Raspovic A, Menz HB. 2001. Reliability of navicular displacement
measurement as a clinical indicator of foot posture. Journal of the American Podiatric
Medical Association 91:262–268 DOI 10.7547/87507315-91-5-262.
Warner MB, Wilson DA, Herrington L, Dixon S, Power C, Jones R, Heller MO,
Carden P, Lewis CL. 2019. A systematic review of the discriminating biomechan-
ical parameters during the single leg squat. Physical Therapy in Sport 36:78–91
DOI 10.1016/j.ptsp.2019.01.007.
Weeks BK, Carty CP, Horan SA. 2012. Kinematic predictors of single-leg squat perfor-
mance: a comparison of experienced physiotherapists and student physiotherapists.
BMC Musculoskeletal Disorders 13:207 DOI 10.1186/1471-2474-13-207.
Wilczyński B, Zorena K, Ślęzak D. 2020. Dynamic knee valgus in single-leg movement
tasks. Potentially modifiable factors and exercise training options. A Literature
Review. International Journal of Environmental Research and Public Health 17:8208
DOI 10.3390/ijerph17218208.
Wyndow N, De Jong A, Rial K, Tucker K, Collins N, Vicenzino B, Russell T, Crossley
K. 2016. The relationship of foot and ankle mobility to the frontal plane pro-
jection angle in asymptomatic adults. Journal of Foot and Ankle Research 9:3
DOI 10.1186/s13047-016-0134-9.

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 12/13

 Yamazaki J, Muneta T, Ju YJ, Sekiya I. 2010. Differences in kinematics of sin-
gle leg squatting between anterior cruciate ligament-injured patients and
healthy controls. Knee Surgery, Sports Traumatology, Arthroscopy 18:56–63
DOI 10.1007/s00167-009-0892-z.
Yokoyama S, Fukuda W, Ikeno Y, Kataoka Y, Horan SA. 2021. Lower limb kinematics of
single-leg squat performance in patients with anterior cruciate ligament deficiency.
Journal of Physical Therapy Science 33:429–433 DOI 10.1589/jpts.33.429.
Zuil-Escobar JC, Martínez-Cepa CB, Martín-Urrialde JA, Gómez-Conesa A. 2018.
Medial longitudinal arch: accuracy, reliability, and correlation between navicular
drop test and footprint parameters. Journal of Manipulative and Physiological
Therapeutics 41:672–679 DOI 10.1016/j.jmpt.2018.04.001.

Guillén-Rogel et al. (2022), PeerJ, DOI 10.7717/peerj.12990 13/13