Does squat technique matter? - Back squat kinetic and kinematic analysis Stefán Ingi Jóhannsson - Skemman
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Does squat technique matter?
Back squat kinetic and kinematic analysis
Stefán Ingi Jóhannsson
Thesis for the degree of Master of Science in Physical Therapy
June 2021
Does squat technique matter?
Back squat kinetic and kinematic analysis
Stefán Ingi Jóhannsson
Thesis for the degree of Master of Science in Physical Therapy
Number of credits: 30
Supervisor: Atli Ágústsson
Department of Physical Therapy
Faculty of Medicine
School of Health Sciences
June 2021
Skiptir hnébeygjutækni máli?
Lífaflfræðileg greining bakstöðu hnébeygju
Stefán Ingi Jóhannsson
Ritgerð til meistaragráðu í sjúkraþjálfun
Fjöldi eininga: 30
Umsjónarkennari: Atli Ágústsson
Námsbraut í sjúkraþjálfun
Læknadeild
Heilbrigðisvísindasvið Háskóla Íslands
Júní 2021
Thesis for Master's degree in Physiotherapy at the University of Iceland. No part of this publication may be reproduced in any form without the prior permission of the copyright holder. © Stefán Ingi Jóhannson, 2021 Printing by: Háskólaprent Reykjavík, Iceland 2021
Abstract
Introduction: The back squat is considered safe if performed correctly. However, there is a
disagreement in current literature about correct squat performance.
Aim: The primary goal of this research is to compare knee, hip, and trunk moments between
normal and hip-hinge squat, which are two different technical variations of the back squat that have
recently been recommended. This study also aims to determine which squat technique should be
recommended based on load distribution between body structures.
Methods: Ten male (n =10; 27.4 years ± 4.5 years; 180.4 cm ±7.5; 85kg ± 8kg; mean ± SD )
CrossFit athletes with over five years of squat weightlifting training participated in the research. Each
participant performed loaded (20kg, 60kg, and 100kg) high bar back squats with both techniques.
Markers were placed on pre-determined anatomical landmarks. Kinetic and kinematic data from the
descent and ascent phase of the high-bar back squats was gathered to form results. 3D motion analysis
was used to collect and analyze data. A multiple linear mixed model was used for statistical analysis.
Results: Knee moment was higher in normal squat during descent phase at all knee flexion
angles (p
Ágrip Inngangur: Hnébeygja er talinn örugg æfing ef hún framkvæmd rétt. Hinsvegar er ágreiningur á milli fræðigreina um hvernig rétt hnébeygja er framkvæmd. Markmið: Megin markmið rannsóknarinnar er að bera saman hné, mjaðmar og bol kraftvægi milli normal og hip-hinge hnébeygja, sem eru tvær tækniútærslur af bakhnébeygju sem hefur nýlega verið mælt með að nota. Markmið rannsóknarinnar er einnig að ákveða hvor hnébeygjutæknin ætti að vera mælt með byggt því hvor tæknin dreyfir álaginu betur á milli líkamshluta. Aðferðir: Tíu karlkyns (n =10; 27.4 ár ± 4.5 ár; 180.4 cm ±7.5; 85kg ± 8kg; meðaltal ± SD ) CrossFit íþróttarmenn með yfir fimm ára reynslu í lyftingar þjálfun tóku þátt í rannsókninni. Hver einstaklingur framkvæmdi þyngdar (20kg, 60kg, 100kg) há stangar bakstöðu hnébeygjur með báðum tækni útfærslum. Endurskinskúlur voru settar á valin landamerki. Safnað var gögnum um kraftvægi og hreyfiferla liða úr niður og uppfasa hnébeygjana. Þrívítt hreyfigreiningarkerfi var notað til að safna gögnum og greina. Við tölfræðigreiningu var notast við línulega fjölþáttargreiningu. Niðurstöður: Munur var á hnévægi á milli tækniútfærsla í niðurfasa hnébeygjunnar í öllum beygju gráðum hnés (p
Acknowledgment
The following parties are thanked for their assistance provided to this thesis for a Master's degree in
physical therapy at the University of Iceland.
Atli Ágústsson lector at the physical therapy program, for initial idea and supervision of the
project, statistical analysis, overread, and other factors related to the project.
Emil Karel Einarsson fellow student, for good collaboration in conducting the research.
Guðni Rafn Harðarson assistant at the physical therapy program, for invaluable assistance in
the data processing.
Participants for giving their time to take part in the study.
Physical therapy program for the use of equipment.
World Class for lending squat rack, barbell, and plates.
v
Table of contents
Abstract.................................................................................................................................................... iii
Ágrip ........................................................................................................................................................ iv
Acknowledgment ...................................................................................................................................... v
Table of contents ..................................................................................................................................... vi
List of figures .......................................................................................................................................... vii
List of tables ........................................................................................................................................... vii
Introduction ..........................................................................................................................................1
1.1 Squat techniques ........................................................................................................................ 2
1.2 Normal and Hip hinge squat ....................................................................................................... 3
1.3 CrossFit ....................................................................................................................................... 3
Aims .....................................................................................................................................................5
Methods ...............................................................................................................................................6
3.1 Design ......................................................................................................................................... 6
3.2 Participants ................................................................................................................................. 6
3.3 Infection control:.......................................................................................................................... 6
3.4 Equipment and setup .................................................................................................................. 6
3.5 Setup of markers......................................................................................................................... 7
3.6 Squat instructions ....................................................................................................................... 7
3.7 Data collection ............................................................................................................................ 8
3.8 Data processing and statistical analysis ..................................................................................... 9
3.9 Ethics ........................................................................................................................................ 12
Results ...............................................................................................................................................13
4.1 20kg barbell .............................................................................................................................. 13
4.2 60kg barbell .............................................................................................................................. 16
4.3 100kg barbell ............................................................................................................................ 19
Discussion ..........................................................................................................................................22
5.1 Main results ............................................................................................................................... 22
5.2 Knee, hip, and trunk moment difference between the two techniques ..................................... 22
5.3 Knee position ............................................................................................................................ 24
5.4 Limitations ................................................................................................................................. 25
5.5 Implications ............................................................................................................................... 25
5.6 Future research......................................................................................................................... 26
Conclusion .........................................................................................................................................27
References .............................................................................................................................................28
Appendix I ...............................................................................................................................................31
Appendix II ..............................................................................................................................................32
vi
List of figures
Figure 1. Markers arrangement in back view from V3D .......................................................................... 7
Figure 2. Markers arrangement in front view from V3D. ......................................................................... 7
Figure 3. Example of position when 30° knee flexion were marked ..................................................... 10
Figure 4. Example of position when 60° knee flexion were marked ..................................................... 10
Figure 5. Example of position when 90° knee flexion were marked ..................................................... 11
Figure 6. Example of position when 120° knee flexion were marked ................................................... 11
Figure 7: Knee moment during the ascent and descent phase of the 20kg squats. ............................. 14
Figure 8. Hip moment during the ascent and descent of the 20kg squats ............................................ 15
Figure 9. Trunk moment during the ascent and descent phase of the 20kg squats ............................. 15
Figure 10. Knee moment during the ascent and descent phase of the 60kg squats ............................ 17
Figure 11. Hip moment during ascent and descent phase of the 60kg squats ..................................... 18
Figure 12. Trunk moment during ascent and descent phase of the 60kg squat. .................................. 18
Figure 13. Knee moment during ascent and descent phase of the 100kg squats ................................ 20
Figure 14. Hip moment during the ascent and descent phase of the 100kg squats ............................. 21
Figure 15. Trunk moment during the ascent and descent phase of the 100kg squat ........................... 21
List of tables
List of tables
Table 1. Technique 1, Normal squat stance, descent phase, and ascent phase instructions ................ 8
Table 2. Technique 2, Hip-hinge squat stance, descent phase, and ascent phase instructions ............ 8
Table 3. Fixed effect multiple linear mixed model, 20 kg squat moments ............................................ 13
Table 4. Estimated marginal means, 20kg squat moments .................................................................. 13
Table 5. 20kg squat mean moment difference ...................................................................................... 14
Table 6. Fixed effect multiple linear mixed model, 60 kg squat moments ............................................ 16
Table 7. Estimated marginal means, 60kg squat moments .................................................................. 16
Table 8. 60kg squat mean moment difference ...................................................................................... 17
Table 9. Fixed effect multiple linear mixed model, 100 kg squat moments .......................................... 19
Table 10. Estimated marginal means, 100kg squat moments .............................................................. 19
Table 11. 100kg squat mean moment difference ................................................................................. 20
vii
Introduction
The squat is a popular exercise to improve lower body strength and function. The squat is often a part
of in and off-session programming in many sports and is also part of a weightlifting, powerlifting, and
CrossFit competition. Besides the obvious health benefits of regular resistance training (Westcott, 2012),
the squat has been considered superior to other exercises to improve functional strength (Rossi et al.,
2018; Padulo et al., 2017; Clark et al., 2012). Increased squat strength has also been linked to enhanced
sports performance, like sprint speed and vertical jump height (Wisløff et al., 2004).
Depending on the purpose and context, squats are performed at various depths and with or
without external load. Squat depths have numerous definitions in the literature. They are often
characterized according to knee flexion angle reached in the squat descent phase. Common squat depth
definitions are; Quarter squat (40-60° knee flexion), Parallel squat (100° knee flexion), and deep or full
squat (greater than 100° knee flexion) (Pallarés et al., 2020; Rhea et al., 2016; Schoenfeld, 2010). The
squat can be broken into two phases. First, the descending phase, primarily eccentric muscle
contraction, is from the erect position to the deepest knee or hip flexion angle. Second, the ascending
phase, mainly concentric muscle contraction, is from the deepest knee or hip flexion angle to erect
standing position (Myer et al., 2014). Most commonly, barbells are used to apply external weight to the
squat in one of two ways. 1: the barbell is placed in front of the neck on the shoulders and/or the chest,
called the “front squat.” 2: the barbell is placed behind the neck on the shoulders/upper back, called the
“back squat” (Russel & Phillips, 1989) . There are two different variations of back squat; "high-bar back
squat" and "low-bar back squat." A High-bar back squat is when the barbell is centered across the
shoulders just below the spinous process of the C7 vertebra. The low-bar back squat is when the barbell
is centered further down the back across the spine of the scapula (WRETENBERG et al., 1996). Here,
the back squat will be discussed further.
Back squat is considered safe to use for its various benefits when performed correctly (Hartmann et
al., 2013). For example, in weightlifting and powerlifting, where athletes undergo squat training regularly
with heavy loads, the injury rate is lower than in contact sports (Aasa et al., 2017). But there is a
disagreement in the literature on correct back squat performance. Back squat has been extensively
researched in the past decades. Kinetics, kinematics, and biomechanics of back squat performance at
various depths and barbell positions have mostly been the area of interest. Based on results from
decades of research, several published papers have recently come forward with recommendations on
"correct" squat performance or techniques, which are not consistent with each other (Comfort et al.,
2018; Myer et al., 2014; Schoenfeld, 2010). The subject of this research is to study knee, hip, and trunk
moment when high-bar back squats are performed with two recently recommended back squat
techniques.
11.1 Squat techniques
Schoenfeld et al. (2010) reviewed the literature and provided recommendations on squat performance
based on the existing ankle, knee, hip, and spine kinetic and kinematic data. The author states that
these recommendations ensure optimal squatting performance and safety and can be summarized as
follows. Squat depth, bar position, and stance should be in context with the purpose of the exercise and
individual variance. The feet should be positioned in a comfortable setting that allows the knees to move
in line with the toes. The lifter should sit back into the squat during the descent and resist pushing the
knees forward with no varus or valgus motion throughout exercise performance. There should be no
posterior pelvic tilt during the squat performance. Attempts should be made to keep the trunk as upright
as possible with no lateral trunk movement (Schoenfeld, 2010). Limitation to these recommendations
is the assumption that it applies to all barbell positions (e.g., front squat, high-bar back squat, and low-
bar back squat). It is well known that there are biomechanical differences between barbell positions, so
one technical approach perhaps does not apply to all squat variations (Glassbrook et al., 2019;
Glassbrook et al., 2017; Yavuz et al., 2015).
Myer et al. (2014) came forth with a Back Squat Assessment screening tool to assist
practitioners in systematically assessing back squat performance. The purpose of the screening tool is
to identify deficits from desired back squat technique. When implemented, the individual performs ten
high-bar back squats with stance position approximately shoulder-width apart and toes pointing forward
or slightly outward. Descriptions of the desired high-bar back squat technique regarding the performance
of the squat descent and ascent phase are thorough but can be summarized as follows. The descent
phase is initiated by breaking at the hips and sitting back as if sitting on a chair that is slightly too far
away. The goal should be to keep their rear as far away from their ankles while maintaining an upright
torso. During the ascent, the torso should remain upright, and the shoulders and hips should rise at the
same pace. Throughout the squat, the knee should track in line with toes with no medial or lateral
movement, and the trunk should be kept in neutral alignment (Myer et al., 2014). There is a similarity
between Myer et al. (2014) and Schoenfeld et al. (2010) squat techniques. Both authors recommend
initiating the squat by sitting back and reducing knee forward movement by either resisting pushing the
knees forward or maintaining the rear as far from the ankles as possible. They also recommend keeping
an upright trunk position throughout the squat. To be able to sit back during squat, knee forward
movement must be reduced. When forward knee movement is reduced, compensatory hip flexion or
trunk flexion must be made to prevent backfall (Fry et al., 2003; List et al., 2013; Lorenzetti et al., 2012).
So, an attempt to reduce forward knee movement and maintaining as upright trunk position as possible
during a back squat performance is contradictory.
Comfort et al. first published back squat technical recommendations in 2007, and they revisited
the article in 2018 with similar findings. Their recommendations are based on evidence from existing
literature about knee forces, trunk position, muscle activation, and effects of squat depth on joints and
performance. They concluded an optimal back squat technique that minimizes the risk of injury and
ensures maximal activation of the lower limb muscles. The technique is summarized as follows. Natural
stance width and foot positioning, with unrestricted movement of the knees. Squat to full depth if the
spine is maintained in a neutral position with knees tracking in line with the toes and no knee valgus
2(Comfort et al., 2018). The limitation to these recommendations is that there is no specific guidance
about the performance of the ascending phase. It is also unclear what the authors mean by unrestricted
knee forward movement. Their argument is based on research by Fry et al.(2003), which shows that if
knees are not allowed to come over the toes, it dramatically increases hip moment and lumbar shear
force by greater trunk inclination (Fry et al., 2003). Therefore, unrestricted knee forward movement can
be interpreted as necessary knee forward movement to maintain an upright trunk position.
1.2 Normal and Hip hinge squat
Authors of aforementioned back squat technical recommendations agree on stance width, foot
positioning, and spine/trunk alignment (Comfort et al., 2018; Myer et al., 2014; Schoenfeld et al., 2010).
They disagree on how the squat descending phase should be initiated and if forward knee movement
should be resisted or unrestricted. Most likely, the authors agree that the ascending phase should be
performed by extending the hips and knees simultaneously and maintaining an upright trunk position by
not allow hips to rise or shoulders to drop forward.
The recommendations can be interpreted as two technical variations which will be referred to
as "normal" and "hip hinge" squat techniques in this manuscript. Normal squat focuses on sitting straight
down to full depth and allowing necessary knee forward movement to maintain an upright trunk position.
Hip hinge squat focuses on initiating the squat by breaking at the hips and sitting back and down to full
depth, resisting pushing the knees forward by sitting back but maintaining as upright trunk position as
possible. Both variations have the same stance, feet position, and trunk alignment. That is feet shoulder
with apart, toes pointing forward, or slightly outward and neutral trunk alignment. Both techniques also
focus on extending the knees and hips simultaneously and maintaining upright trunk position by not
allowing hips to rise or shoulders to drop forward.
1.3 CrossFit
CrossFit is: "constantly varied, high – intensity functional movement." (CrossFit, 2019a) CrossFit is both
a sport and a method to get into or maintain a healthy physical shape. Athletes who compete in CrossFit
at the highest level must both be physically strong and have tremendous endurance to excel in the sport.
On top of that, CrossFit athletes must have the flexibility and skill to perform complex gymnastic and
weightlifting movements. Weightlifting is a large part of CrossFit athlete's strength program, and they
incorporate high-bar back squats in their training to enhance performance (Crossfit, 2019a). CrossFit
competition events include squats in many variations (i.e., front squats, back squats, overhead squats,
bodyweight squats, single-leg squats, cleans, and snatches. The training volume and intensity are high
in those competition events. That is, many repetitions are completed in as short time as possible. For
example, the top 10 male competitors competing at the 2019 CrossFit Games, which the best CrossFit
athletes in the world compete in, did 232-297 squat repetitions over four days and 12 workouts. The
load was light (single leg squat) to heavy (143kg -172kg squat cleans). The standard for a valid squat
in CrossFit competition is that hip crease bellow parallel to the knee in the bottom position, and then
3hips and knees are fully extended to finish the repetition (Crossfit, 2019b). Valid squat depth standard
falls into a deep squat definition mentioned earlier.
To coach and teach others CrossFit in a licensed CrossFit affiliate, you must clear a CrossFit
Level 1 Trainer Course. In the level 1 course training guide manual, under "How to Squat," 22 cues to a
proper squat are labeled. During the descent phase of the squat, "send your butt down and back" and
"delay the knees forward travel as much as possible" are among those cues (CrossFit, 2019a). Those
ques are similar to the hip hinge squat technique.
Injury prevalence among CrossFit athletes and practitioners has been an increasing area of
interest in the literature. According to a recent systematic review, shoulders, knee, and spine is the most
commonly injured body parts in CrossFit (Rodríguez et al., 2021). Perhaps in sports like CrossFit, which
often includes high repetition squat movements with varying loads, correct or most efficient squat
technique is even more warranted to reduce the risk of injury.
4Aims
The primary goal of this research is to compare knee, hip, and trunk moments between normal and hip-
hinge squat, which are two different technical variations of the back squat that have recently been
recommended. This study also aims to determine which squat technique should be recommended
based on load distribution between body structures. Knee, hip, and trunk moments were examined in
the sagittal plane and compared at different knee flexion angles between normal and hip-hinge squat
techniques during both the descent and ascent phase of the squat. The research question is: Are knee,
hip, and trunk moments different when high-bar back squats are performed with normal and hip-hinge
squat techniques?
The research was conducted with the following hypothesis in mind:
1. Normal squat distributes the load more evenly between knees, hip, and trunk.
2. Hip-hinge squat reduces the load on knees minimally compared to how it increases the load on
hips and trunk during the squat descent phase.
5Methods
3.1 Design
The study design is a cross-sectional study. Each participant performed deep-loaded high-bar back
squats with two different squat techniques (see tables 1 and 2). Results were formed by comparing the
two techniques based on a knee, hip, and trunk moment at different knee flexion angles. Data collection
took place in the Research Center for Movement Sciences at the University of Iceland from the 7th of
August 2020 to the 3rd of September 2020.
3.2 Participants
Data were collected from 10 male crossfitters, aged 21-31 years and 10 basketball players. Data
collected from the basketball players will not be discussed further in this research (see Emil Karel
Einarsson master thesis, 2021). Participants discussed in this research had over five years of
purposeful CrossFit and weightlifting training. Participants were identified by searching CrossFit gyms
in Reykjavík, Iceland, and asked to take part in the study. Participants needed to be injury-free so squat
performance would not be affected. It was important that participants were experienced with the high-
bar back squat movement and capable of squatting 100kgs with minimal effort.
3.3 Infection control:
Measurements stood over the Covid-19 pandemic. Therefore, it was an urgent need to respect
published infection control guidance. All participants were given masks and rubber gloves at arrival and
asked to keep on during the measurements. All contact surfaces were cleaned after the participant left
the research lab.
3.4 Equipment and setup
Participants performed the high-bar back squats on two force plates (Amti, Watertown, MA, US). Around
the force plates were 8 Qualysis Oqus 300 3D cameras (Qualsisys, Göteborg, Sweden) that recorded
the squats at the frequency 400 Hz. In front of the force plates was a squat rack adjusted to an
appropriate height for each participant. On the squat rack rested Rogue 2.0 bar (Rogue, Columbus, OH,
USA) and, four 20kg Eleiko (Eleiko, Halmstad, Sweden) plates were used to load the barbell to 60 and
100kgs. Reflective markers were placed on each participant at pre-determined anatomical locations. A
wand was used to calibrate the area where the squats were performed. Height meter and weight scale
were also used.
63.5 Setup of markers
To define the position and location of joints and
barbell were 58 reflective markers used. The
reflective markers were placed evenly on each
participant's body half on pre-determined
anatomical landmarks. C-Motion Marker Set
Guidelines (C-motion, 2015) were used for
placement of markers to define foot, shin, thigh,
hip, spine, vertebral column, and shoulder girdle.
The arrangement is shown in figure 1 and figure 2
and was as follows: manubrium of the sternum,
T10, inferior angle the scapula, acromion, iliac
crest, anterior superior iliac spine, sacrum, Figure 2. Markers arrangement in front view from V3D.
posterior superior iliac spine, greater trochanter,
medial femoral condyle, lateral femoral condyle,
medial malleolus, lateral malleolus, upper and
lower calcaneus, first metatarsal, second
metatarsal, and fifth metatarsal. Also, two clusters
with four markers were placed on the mid-shin and
thigh. The bar was defined with eight markers, six
spread evenly along the length of the bar and two
on mid scapula below where the bar rested on the
participant's shoulders. Placements of the bar's
markers were determined after testing, but no
model or instructions were found for this research.
Figure 1. Markers arrangement in back view from V3D
The markers were on the participant during the
measure and were only taken off after the measurement was completed.
3.6 Squat instructions
Instructions were given and showed to participants before they warmed up to practice the techniques
as needed. In all squat technique's participants were instructed to begin with hips and knees fully
extended, squat to full depth, and finish the repetition with hips and knees fully extended. For a squat to
be valid, it needed to begin and end with hips and knees fully extended, and hips required to at least
creep bellow parallel to the knee in the sagittal plane. All squats were high-bar back squats and
performed barefooted.
Each participant performed three high-bar back squats with five different squat techniques with 20kg,
60kg, and 100kg loaded barbell, a total of 45 squats. Squat instructions about stance, foot position,
descent, and ascent phase are shown in tables 1 and 2 and Appendix II. Only data from technique 1
(normal squat) and technique 2 (hip-hinge squat) were used in this research.
7Table 1. Technique 1, Normal squat stance, descent phase, and ascent phase instructions
Instructions
Stance Keep feet shoulder with apart, and toes pointed forward or
slightly outward.
Descent phase Focus on sitting straight down and allow knees to come
forward as needed to maintain upright trunk position. Maintain
complete contact with your feet on the floor and do not allow
heels to rise.
Ascent phase When you reach full depth, stand straight up, and do not allow
shoulders to fall forward or hips to rise too fast.
Table 2. Technique 2, Hip-hinge squat stance, descent phase, and ascent phase instructions
Instructions
Stance Keep feet shoulder with apart, and toes pointed forward or
slightly outward.
Descent phase Focus on breaking at the hips and sit back and down. Resist
pushing the knees forward but try to stay as upright as you
can. Maintain complete contact with your feet on the floor and
do not allow heels to rise.
Ascent phase When you reach full depth, stand straight up, and do not allow
shoulders to fall forward or hips to rise too fast.
3.7 Data collection
Measurements were performed at the Research Center for Movement Sciences at the University of
Iceland. All measurements for each participant were completed in a single session that took around 45
minutes.
At arrival was each participant asked to read and sign an informed consent to partake in the study.
Next, each participant was height and weight measured, and information listed down. Squat instructions
were then given to the participant (see tables 1,2, and appendix II), and the participant was given time
8to warm up as he would typically do before squatting. Participants were allowed to practice the different
squat techniques as they pleased. When the participant was ready to begin and researchers approved
the performance of the squats, reflective makers were placed on the participant.
Measurements started with an empty 20kg barbell. The participant unracked the bar and
walked onto the force plates, and a static measurement was taken. The purpose of static measurement
was so Qualisys Tracking Manager (Qualisys, Göteborg, Sweden) motion capture program could use
the reflective markers to define body parts, joint center and acquire a 3D position of each participant.
Qualisys Tracking Manager also sampled data from the cameras and force plates. After static
measurement was recorded, the participant stepped of the force plates to get ready for squat
measurements. In all squat measurements, participants were asked to step in front of the force plates
and were then counted down to step onto plates, begin squatting and step of the force plates as soon
as three valid repetitions were completed. This was repeated until the participant had finished three valid
squats with all five squat techniques. Then the bar was loaded to 60kg and lastly 100kg and the flow
repeated. Participants were allowed to rerack the bar between each set of 3 squats and rest as needed.
3.8 Data processing and statistical analysis
Data digitizing started in Qualisys Tracking manager, where it was made sure that anatomical landmarks
were marked as intended, both in static measurements and squat measurements. Then data was
opened in Visual 3D (V3D) software (C-motion Germantown, MD, US), a specialized program for kinetic
and kinematic data processing. In V3D, the height and weight of the participants and the weight of the
barbell were added to each static measurement. Kinetic and kinematic parameters were calculated out
of 3D data in V3D. Looked was to X-axis in the kinetic and kinematic data processing. The X-axis (e.g.,
sagittal plane) represents flexion and extension angles and moments during the squat performance.
Knee flexion and extension angles at 30°,60°,90° and 120° were marked in all measurements in V3D
(see figure 3-6). Knee, hip, and trunk moment were then exported out of V3D at 30°,60°,90°, and 120°
knee flexion and extension. Exported data was opened Excel for organizing and preparation for
statistical analysis.
Jamovi, a statistical spreadsheet software which is built on top of the R statistical language, was used
for statistical analysis (The jamovi project, 2021). A multiple linear mixed model was used to estimate
the parameters of a linear relationship between the moment and the independent variables. Fixed effect
Omnibus tests were used to see a statistical difference in main effects and interactions between squat
techniques and degrees of knee flexion. One-way repeated ANOVA was used to look for statistical
differences in knee, trunk, and hip moment between squat techniques at different knee flexion angles.
Holm Post Hoc Test was used to explore interactions or statistical differences further. The criterion for
the statistical difference was set at (pFigure 3. Example of position when 30° knee flexion were marked
in V3D. Left is normal squat, right is the hip-hinge squat.
Figure 4. Example of position when 60° knee flexion were marked
in V3D. Left is normal squat, right is the hip-hinge squat.
10Figure 5. Example of position when 90° knee flexion were marked
in V3D. Left is normal squat, right is the hip-hinge squat.
Figure 6. Example of position when 120° knee flexion were marked
in V3D. Left is normal squat, right is the hip-hinge squat.
113.9 Ethics
Participants needed to receive information about the purpose, reasoning, and content of this research
so they could make an informed decision to participate. No participant was injured or harmed in this
study. All participants signed an informed consent where all personal data would be discarded, and they
could drop out at any time and without reasoning. Science Ethics Committee approved the research
(Reference number of approval from the Science Ethics Committee is VSNb2020050022/03.01).
Participants were insured during measurements.
12Results
Ten male crossfiters participated in the study with a mean age of 27,4 years (SD ± 4.5 years), the mean
height of 1.80 m (SD ± 7.5 cm), and a mean weight of 85kg (SD ± 8kg).
4.1 20kg barbell
There was a difference in all moments between the two techniques (normal and hip-hinge), both in
the descent and ascent phase of the squats (see table 3 and 4). There was interaction in both trunk and
hip moment between squat techniques and degrees of knee flexion during the descent phase of the
squats (see table 3). Knee moment was higher in the normal squat compared to hip hinge squat in both
ascent and descent phase of the squats (see table 5). Trunk and hip moments were higher in hip hinge
squat than normal squat in both descent and ascent phase of the squats (see table 5). To graphically
see the linear curve of moments at increasing and decreasing knee angles, see figure 7-9.
Table 3. Fixed effect multiple linear mixed model, 20 kg squat moments. a) Squat = difference in moment
between normal and hip hinge squat, b) Degree = changes in moment with increasing knee
flexion angle, c) Repetition = difference in moment between repetitions d) Squat✻ degree =
interaction between squat technique moments in relation to knee flexion angles.
Knee moment Hip moment Trunk moment
Descent Ascent Descent Descent
Ascent phase Ascent phase
phase phase phase phase
F p F p F p F p F p F p
Squat 55 < .001 9 < .003 202 < .001 20.8Table 5. 20kg squat mean moment difference (MD) between techniques at different knee flexion angles.
Orange color (normal – hip-hinge), Blue color = (hip-hinge – normal)
Knee moment Hip moment Trunk moment
Descent Ascent Descent Ascent Descent Ascent
phase phase phase phase phase phase
Knee flexion MD p MD p MD p MD p MD p MD p
30° 0.09 0.007 0.01 0.871 0.43Figure 8. The graph shows the hip moment during the ascent and descent phase of the 20kg squats.
Mean hip moment and 95% confidence intervals are shown. According to the Holm Post Hoc
test, was mean hip moment 0.32 Nm/kg (p4.2 60kg barbell
There was a difference in moments between the two squat techniques. Knee moment was different
during descent phase, hip and trunk moment was different in both descent and ascent phase (see table
6 and 7). There was interaction in both hip and trunk moment between squat techniques and degrees
of knee flexion (see table 6). Table 8 shows the difference in moments between techniques at different
knee flexion angles. To graphically see the linear curve of mean moments at increasing and decreasing
knee angles, see figure 10-12.
Table 6. Fixed effect multiple linear mixed model, 60 kg squat moments. a) Squat = difference in moment
between normal and hip hinge squat, b) Degree = changes in moment with increasing knee
flexion angle, c) Repetition = difference in moment between repetitions d) Squat✻ degree =
interaction between squat technique moments in relation to knee flexion angles.
Knee moment Hip moment Trunk moment
Descent Ascent Descent Ascent Descent Ascent
phase phase phase phase phase phase
F p F p F p F p F p F p
Squat 129 < .001 3.68 0.057 184 < .001 8.7 0.004 216 < .001 11.9 < .001
Degree 738 < .001 880.5Table 8. 60kg squat mean moment difference (MD) between techniques at different knee flexion angles.
Orange color (normal – hip-hinge), Blue color = (hip-hinge – normal)
Knee moment Hip moment Trunk moment
Descent Ascent Descent Ascent Descent Ascent
phase phase phase phase phase phase
Knee flexion MD p MD p MD p MD p MD p MD p
30° 0.14Figure 11. The graph shows hip moment during the ascent and descent phase of the 60kg squats.
Mean hip moment and 95% confidence intervals are shown. According to the Holm Post Hoc
test, was mean hip moment 0.46 Nm/kg (p4.3 100kg barbell
Knee and hip moment were different in the squat descent phase between the two techniques (see table
9 and 10). The trunk moment was different, both in the descent and ascent phase of the squat between
the two techniques (see table 9). There was interaction in both hip and trunk moment between squat
techniques and degrees of knee flexion during the descent phase of the squats (see table 9). Table 11
shows the mean moment difference between squat techniques at different knee flexion angles. To
graphically see the linear curve of mean moments at increasing and decreasing knee angles, see figure
7-9.
Table 9. Fixed effect multiple linear mixed model, 100 kg squat moments. a) Squat = difference in
moment between normal and hip hinge squat, b) Degree = changes in moment with increasing
knee flexion angle, c) Repetition = difference in moment between repetitions d) Squat✻ degree
= interaction between squat technique moments in relation to knee flexion angles.
Knee moment Hip moment Trunk moment
Descent Ascent Descent Ascent Descent Ascent
phase phase phase phase phase phase
F p F p F p F p F p F p
Squat 102Table 11. 100kg squat mean moment difference (MD) between techniques at different knee flexion
angles. Orange color (normal – hip-hinge), Blue color = (hip-hinge – normal)
Knee moment Hip moment Trunk moment
Descent Ascent Descent Ascent Descent Ascent
phase phase phase phase phase phase
Knee
MD p MD P MD p MD p MD p MD p
flexion
30° 0.14 0.003 0.06 0.263 0.93Figure 14. The graph shows hip moment during the ascent and descent phase of the 100kg squats.
Mean hip moment and 95% confidence intervals are shown. According to the Holm Post Hoc
test, was hip moment 0.55 Nm/kg (pDiscussion
5.1 Main results
The main findings of this study are that there was a difference in the knee, hip, and trunk moment
between the two squat techniques. Mean knee moment was significantly higher in the normal squat
when compared to hip hinge squat during the whole descending phase, independent of barbell weight.
Trunk and hip moment were significantly higher in hip hinge squat when compared to normal squat
during the first 90° knee flexion of the descending phase, independent of barbell weight. There was an
interaction between the trunk and hip moment and degrees, independent of barbell weight. The most
considerable mean trunk and hip moment difference between the two techniques was during the first
60° knee flexion. The ascending phase was more similar between the two techniques, and the difference
got smaller with increasing barbell weight. There were fewer interactions between moment and degrees
of knee flexion and minimal difference in the mean knee, trunk, and hip moment between the two squat
techniques compared to the descending phase. Hypothesis 1 was accepted that normal squat
distributes the load more evenly between knee, hip, and trunk. Hypothesis 2, that hip hinge squat
reduces the load on the knees minimally compared to the load it adds on hips and trunk, was also
accepted.
5.2 Knee, hip, and trunk moment difference between the two techniques
Knee moment during a squat has been found to increase with knee flexion and reduce with knee
extension (Cotter et al., 2013; ESCAMILLA et al., 1998; Krzyszkowski & Kipp, 2020; Lander et al., 1986;
Lorenzetti et al., 2012; Wu et al., 2011). Knee moment has also been found to increase with forwarding
knee movement (Chiu et al., 2017; Fry et al., 2003; Hirata & Duarte, 2007; Lorenzetti et al., 2012). When
the knees come forward during squat by ankle dorsiflexion, the weight shifts anteriorly. That anterior
weight shift increases knee extension muscle activity demand to maintain position and control the
descent. Results from this study show that as the knees move anteriorly, the knee moment rises. Knee
moment was higher in normal squat throughout the squat descent phase in all barbell weights. A minor
moment difference was at 30° knee flexion, but from 60°-120° the moment difference was relatively
equal, which explains why there was no interaction between knee moment and degrees. Since all
moments are compared at the same knee flexion angle, the difference in knee moment between the
techniques is mainly explained by increased knee forward movement in the normal squat. The most
considerable difference in knee moment between the techniques was with 100kg barbell and ranged
from 0.14 Nm/kg – 0.32 Nm/kg.
A primary factor that increases trunk moment during a squat has previously been found to be
trunk inclination. (Potvin et al., 1991; Russell & Phillips, 1989) The further the trunk leans forward during
a squat, the more back extension muscle activity demand is needed to maintain trunk alignment. Our
results show that the most significant trunk moment difference between the two techniques in all barbell
weights was in the first 60° of knee flexion. The trunk moment difference then drastically reduced as the
knee progressively flexed, and at 120° knee flexion was no or minimal difference in trunk moment. Hip-
22hinge squat trunk moment increased rapidly from 0° to 60° knee flexion and then increased minimally in
the remaining of the descent, but normal squat trunk moment increased progressively throughout the
descent (see figure 9,12,15). This difference in trunk moment rise between the two techniques explains
the interaction between trunk moment and degrees of knee flexion. The main explanation for this large
difference between techniques at the beginning of the descent is by the nature of the hip hinge squat
technique. When the squat is initiated by breaking at the hips and sitting back, increased trunk inclination
is needed to maintain balance and prevent backfall. That results in significantly more back extension
demand at the beginning of the descending phase. The most significant trunk moment difference was
with the 100kg barbell. There the difference peaked at 1.2Nm/kg at 30° knee flexion.
Hip moments during a squat have previously been found to increase with hip flexion
(Krzyszkowski & Kipp, 2020; Lorenzetti et al., 2012). The hip moment has also been found to have a
relationship with forwarding knee movement (Fry et al., 2003; Krzyszkowski & Kipp, 2020; Lorenzetti et
al., 2012; McLaughlin et al., 1978). When forward knee movement is restricted or reduced, the weight
shifts to the rear and increased hip flexion is needed to keep weight within the base of support.
Therefore, reduced knee forward movement yields increased hip extension muscle activity demand to
maintain balance and position. Our results show that hip moment was significantly higher in hip hinge
squat when compared to normal squat in the first 90° knee flexion of the descending phase in all barbell
weights. But at 120° knee flexion of the descending phase, there was no difference in the hip moment
between the two techniques. The hip moment followed a similar linear curve as the trunk moment. In
hip hinge squat, the hip moment also increased rapidly in the first 60° of knee flexion but grew little in
the remaining of the descent phase (see figure 8,11,14). In the normal squat, the hip moment
progressively increased throughout the descending phase, explaining the interaction between hip
moment and degrees of knee flexion. The most considerable difference in the hip moment between the
techniques was 0.93 Nm/kg at 30° knee flexion of the descending phase with 100kg barbell. As in trunk
moment, the nature of the hip hinge squat technique explains this significant difference in the hip
moment between the two techniques. Initiating squat by breaking at the hip, sitting back, and resisting
pushing knees forward shifts the weight to the rear and increases hip flexion. Therefore, increased trunk
inclination at the beginning of the descent is needed to maintain balance and position. The result is
significantly more extension muscle activity demand of hips and trunk.
Squat instructions most likely explain the similarity in the ascending phase between the two
techniques. The instructions were identical in both techniques, so similarity was to be expected. There
was some difference in moments between techniques in the ascending phase with 20 kg and 60 kg
barbell. However, with 100kg barbell, the ascending phase was almost identical between the two
techniques. It indicates that participants maintained reduced knee forward movement during the
ascending phase in the hip hinge squats with lighter weights. Therefore, increased hip flexion was
needed, which resulted in a difference between the two techniques. But with 100kg barbell, there was
almost no difference in the knee, trunk, and hip moments between the two techniques. Either
participants felt more comfortable performing the ascending phase in a certain way with heavier weights
or could not maintain a difference in position.
235.3 Knee position
Our results demonstrate the importance of knee position during a high-bar back squat. When forward
knee movement is reduced, even at small knee flexion angles, it affects hip and trunk position, resulting
in higher muscle activity demand for those body structures to maintain balance and position. Restriction
to forward knee movement during a back squat has been studied and compared to unrestricted knee
forward movement and show similar results (Chiu et al., 2017; Fry et al., 2003; Hirata & Duarte, 2007;
List et al., 2013). Forward knee movement was either limited with a fixed object in front of the knees or
a visual cue. That led to hip moment difference at the end of descending phase, which is not consistent
with the results of this study. In hip hinge squat, forward knee movement was not restricted but instructed
to be resisted. That means that during hip hinge squat, knees came forward at the end of the descent
to prevent the trunk from falling forward, highlighting the importance of knee position during the squat.
Back squat recommendations similar to hip-hinge squat instructions in this study have been considered
optimal or desired back squat technique (Kushner et al., 2015; Myer et al., 2014; Schoenfeld, 2010).
The basis for the recommendation is when forward knee movement is reduced, either by resisting it or
sitting back motion, allows the load to be supported by the posterior chain, and reduces the load on
knees during the squat descent. The need to reduce the load on knees is not in compliance with
documented squat knee forces. A recent extensive review of squat knee and trunk forces demonstrates
that knee forces do not harm the knees during a deep squat performance (Hartmann et al., 2013). The
author also states that instructions about the limitation to forward knee movement should be strictly
avoided, and a misinterpretation of existing data and should be removed from future practical literature.
That is consistent with results from Comfort, McMahon et al. (2018), who recommend back squat to be
performed with unrestricted knee forward movement and an upright trunk position should be maintained,
which is similar to normal squat instructions in this study. It seems necessary to allow the knees to come
forward as needed to maintain an upright trunk position and distribute the load evenly between the knee,
hips, and tunk throughout the squat descending phase. Also, breaking at the hips and sitting back seems
to decrease the load on the knees minimally compared to how it increases the load on the trunk and
hips at the beginning of the descent phase.
245.4 Limitations
A larger sample size would have increased the statistical power of the research. One of the admission
requirements was to be experienced with high bar back squats and capable of lifting 100kg with minimal
effort. Even though participants had currently been training CrossFit and weightlifting for over five years,
it does not mean they were equally strong. Information about high bar back squat one repetitions
maximum was neither established nor noted. Stricter admission requirements, for example, all
participants need to have one repetition maximum in a high bar back squat within 20kgs from 200kgs,
would have made the performance of the squats more equal and results of the research clearer.
Performing squats after specific instructions on their leads to measurement error. The
participants were either more experience with one of the squat techniques, or their own technique lies
somewhere between. A squat is a complicated movement, and squatting with a new technique,
especially after external guidance, is hard to implement consistently. There was some variability
between repetitions, even though it was not statistically significant.
There was no requirement to rest for a certain period before participating in this research. It's
unlikely that participants considered participation in the study a workout after receiving information about
what was required of them. Even though barbell weights were light for the participants, the volume was
high. If a participant was sore or tired after a hard training week at arrival, fatigue could have affected
consistency in performance.
As mentioned before, there was no model found for the definition of the barbell. If the barbell
can be defined more precisely, it could affect the results of this study. Finally, only kinematic data from
the knee joint was used. Differences in moments between techniques are explained with assumptions
from other research results. A more holistic approach would include kinematic data about the ankle,
trunk, and hip angles to support results.
5.5 Implications
Normal and hip-hinge squat techniques were compared based on the knee, hip, and trunk moments at
different knee flexion angles. Extensive kinetic and kinematic data were collected, but only data about
knee flexion, knee moment, hip moment, and trunk moment were used. Results indicate that a normal
squat is more efficient in distributing load between knee, hip, and trunk. Hip hinge squat loads the hips
and especially trunk a lot more at the beginning of the descent phase, potentially leading to unnecessary
injury. Results can be exploited by guiding athletes and the public in high bar back squat performance
to reduce the risk of injury.
Physical therapists must be informedabout the utility and risk of high bar back squat as an
exercise to increase lower body strength and function. Professionals should also be informed about how
structures are loaded when a high bar back squat is performed and how it can be manipulated to suit
individual needs. Part of the physical therapist's care is to guide athletes and the public in selecting
exercises for each individual. If a high-bar back squat brings the individual closer to their own and goals
of care, physical therapists need to be able to instruct them in its implementation and execution.
255.6 Future research
As mentioned earlier, data about the ankle, hip, and trunk angles was not used in this study. It would be
interesting if the integration of that data would change the results of this study. Future research could
also compare the techniques at different planes. For example, see if either technique increases/reduces
medial or lateral stability of the knees. It would also be interesting to compare the techniques when
squats are performed with different barbell positions, for example, front squats or low-bar back squats.
It would be informative to repeat this study on women at the same age. Possibly would have other
stance, and foot positions show different results. Future research could, for example, compare the
techniques at wider stance and toes pointed out. Interesting as well would be to study the techniques
where participants would squat with and without lifting shoes. Lastly, it's worth noting that information
about inner joint forces, like shear and compression forces in mentioned squat techniques, could be a
valuable appendix to this research.
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