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Int J Sports Phys Ther
Int J Sports Phys Ther
2159
International Journal of Sports Physical Therapy
2159-2896
NASMI Website: International Journal of Sports Physical Therapy

38576836
94600
10.26603/001c.94600
Clinical Commentary/Current Concept Review
A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice
Straub Rachel K
Powers Christopher M
Corresponding Author: Christopher M. Powers, PT, PhD, FACSM, FAPTA USC Division of Biokinesiology & Physical Therapy 1540 E. Alcazar St. CHP-155 Los Angeles, CA 90089-9006 Phone: 323.442.1928 Fax: 323.442.1515 Email: powers@usc.edu
1 4 2024
2024
19 4 490501
29 11 2023
7 2 2024
© The Author(s)
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (4.0) which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

The squat is one of the most frequently prescribed exercises in the rehabilitative setting. Performance of the squat can be modified by changing parameters such as stance width, foot rotation, trunk position, tibia position, and depth. An understanding of how the various squatting techniques can influence joint loading and muscular demands is important for the proper prescription of this exercise for various clinical conditions. The purpose of this clinical commentary is to discuss how the biomechanical demands of the squat can be influenced by various modifiable parameters. General recommendations for specific clinical conditions are presented.

Level of Evidence

5

kinetics
kinematics
biomechanics
squatting
clinical commentary
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pmcINTRODUCTION

Squatting is an essential movement pattern for activities of daily living (i.e., toileting and getting into or out of a chair) and various athletic tasks. As such, the squat exercise is commonly used in rehabilitation and sport performance settings to strengthen the primary lower extremity muscle groups (i.e., hip extensors and knee extensors).1–5 In addition, the squat exercise requires a high level of recruitment from the trunk muscles to provide stabilization for the spine and torso.4,6,7

The squat exercise can be highly variable in its execution. For example, the squat can be adapted by modifying trunk position, tibia position, foot rotation, stance width, and depth. Given that each modifiable factor can influence the biomechanics of the squat (i.e., muscular demands, joint loading, etc.), it is not surprising that the literature is conflicting when recommending various squatting techniques for different clinical situations.4,8 Interpretation of research related to squatting is difficult owing to the fact that many studies fail to control for the various modifiable parameters when assessing the influence of a specific variable.

It is important that clinicians be mindful of the various interactions among the modifiable parameters so that correct clinical recommendations can be made. As such, the purpose of this clinical commentary is to discuss how the biomechanical demands of the squat can be influenced by various modifiable parameters. General recommendations for specific clinical conditions are presented. It is hoped that the information presented will assist clinicians in the appropriate prescription of the squat exercise for patients with various diagnoses.

MODIFIABLE SQUAT PARAMETERS

Trunk Inclination

The moments at the hip and knee during squatting are highly influenced by the orientation of the trunk, which in turn affects the center of mass of the body.9,10 During a typical squat, the resultant ground reaction force vector passes anterior to the hip and posterior to the knee, thereby creating flexion moments at both joints (Figure 1).9 Muscular actions of the hip and knee extensors are required to generate extensor moments to counteract these external moments. Moving the trunk from a more upright position (Figure 1A) to more forward position (Figure 1B) shifts the resultant ground reaction force vector anteriorly, resulting in an increase in the hip flexion moment while simultaneously decreasing the knee flexion moment.11 Conversely, moving the trunk from a forward position (Figure 1B) to more upright position (Figure 1A) shifts the resultant ground reaction force vector posteriorly, thereby decreasing the hip flexion moment while simultaneously increasing the knee flexion moment.11

198462 Figure 1. Sagittal plane orientation of the trunk influences the external moments at the hip and knee.

Squatting with the trunk in a more upright position increases the knee flexion moment while decreasing the hip flexion moment. (B) Moving the trunk forward increases the hip flexion moment while decreasing the knee flexion moment.

Apart from its influence on the hip and knee flexion moments, squatting with a forward trunk has an impact on the lumbar spine flexion moment. Generally speaking, the greater the forward trunk inclination, the greater the muscular demand on the back extensors to stabilize the trunk.12 It should be noted however, that forward inclination of the trunk can be obtained through flexion of the hip or flexion of the lumbar spine (Figure 2).13 Attainment of a forward trunk position using lumbar spine flexion (Figure 2A) results in decreased tolerance to compressive loads14 and lumber spine anterior shear forces as compared to when forward trunk inclination is achieved with a neutral spine position (Figure 2B).15 Maintaining a neutral spine position increases the moment arm for the spinal extensors thereby allowing better control of compressive loads and shear forces.14,15

198463 Figure 2. Forward inclination of the trunk that is achieved by spine flexion (A) results in decreased tolerance to compressive loads and less control of anterior shear forces as compared to when forward trunk inclination is achieved with a neutral spine position (B).

Tibia Inclination

Compared to trunk inclination, inclination of the tibia during squatting has an opposite influence on the knee flexion moment.9,10,16–18 Moving the tibia from a more upright position (Figure 3A) to more forward position (Figure 3B) shifts the knee joint center further away from the resultant ground reaction force vector, thereby increasing the knee flexion moment. Conversely, moving the tibia from a forward position (Figure 3B) to more upright position (Figure 3A) shifts the knee joint center closer to the resultant ground reaction force vector, thereby decreasing the knee flexion moment.

198464 Figure 3. Sagittal plane orientation of the tibia influences the external moment at the knee.

Squatting with the tibia in a more upright position decreases the knee flexion moment. (B) Moving the tibia forward increases the knee flexion moment.

Forward tibia inclination can be achieved by either ankle dorsiflexion (with the foot flat on the floor) or squatting with the heels off the floor (i.e., using an external lift under the rearfoot or weightlifting shoes with an elevated heel).19 In general, elevating the heels during squatting facilitates a greater degree of forward tibia inclination, thereby increasing the knee flexion moment and the demand on the quadriceps.19,20 It should be noted however, that the forward tibia position when squatting with the heels elevated can occur without a corresponding increase in ankle dorsiflexion.

Foot Rotation

The degree of foot rotation during squatting can be accomplished by hip external rotation, knee external rotation, or a combination of both. The degree of toe out influences the frontal and transverse plane moments at the knee while having a negligible effect on the sagittal plane moments. For example, rotating the feet outward 30° has been reported to decrease the valgus moment at the knee by 50% while simultaneously increasing the varus moment by 80%.21 In addition, rotating the feet outward 30° decreases the external rotation moment at the knee by 20% when compared to a neutral stance.21

From a muscle recruitment standpoint, rotation of the foot outward 30° has no effect on activation of the quadriceps, hamstrings, or gastrocnemius when compared to a neutral foot position.2,22 Similarly, varying rotations of the tibia and femur from 30° inward to 80° outward has no effect on quadriceps activity.23 However, squatting with the hip externally rotated 30° to 50° has been reported to increase hip adductor activity compared to a neutral stance by 17% and 23% respectively (neutral: 13% of maximum voluntary isometric contraction [MVIC] vs. 17% and 23% MVIC for 30° and 50° rotation, respectively).24

Stance Width

For the purposes of this perspective, the authors operationally define stance width as narrow (75% to 100% shoulder width), medium (100% to 150% shoulder width), or wide (150% to 200% shoulder width). With respect to the frontal and transverse planes, a wide stance results in greater knee valgus moments (23%)25 and higher hip external rotation moments (19%-37%) when compared to narrow/medium stance squats.26 In terms of the sagittal plane, however, the impact of stance width is conflicting.25–27 Compared to a narrow/medium stance, the knee flexion moment during wide stance squatting has been reported to be higher (69%-80%),27 lower (11%),25 or not different.26 Similarly, the hip flexion moment during wide stance squatting has been reported to be higher (10%-48%)26,27 or not different compared to narrow/medium stance squatting.25 The conflicting results among studies can be explained by how authors controlled for other modifiable factors such as trunk and tibia orientation. For example, performing a wide stance squat with the trunk inclined would yield a different result than if the squat was performed with the trunk more upright.

From a muscle recruitment standpoint, a medium/wide stance squat has been reported to result in higher gluteus maximus activity (13%-61%)28,29 and 18% lower gastrocnemius activity (14% vs. 17% MVIC) compared to narrow/medium stance squats.2 Stance width does not appear to influence hamstring,28,29 quadriceps,28,29 or gluteus medius activity.29 In regards to hip adductor recruitment, stance width does not influence overall muscle activation.29 However, if the descending and ascending phases are analyzed separately, a wider stance increases hip adductor activity during the accent phase of squatting compared to the descent phase by approximately 50%.28

Squat Depth

For the purposes of this perspective, the authors operationally define squat depth as partial/shallow (0°-90° knee flexion), medium (90°-110° knee flexion or thigh parallel to floor), or full/deep (110°-135° knee flexion). Generally speaking, the knee flexion moment tends to steadily increase from an upright position to maximum knee flexion during squatting.30–32 Similarly, the hip flexion moment also increases with squat depth.32 However, the increase in the knee flexion moment with greater squat depth is not consistent across studies,33,34 and can be affected by the trunk and tibia orientation. For example, if the increase in trunk inclination with increasing depth is more pronounced than the increase in tibia inclination, this could potentially result in a relatively higher hip flexion moment relative to the knee flexion moment at higher depths. Conversely, if the increase in tibia inclination with increasing depth is more pronounced than the increase in trunk inclination, this could potentially result in a higher knee flexion moment relative to the hip flexion moment at greater squatting depths.

Apart from the influence of squat depth on hip and knee moments, studies examining muscle recruitment with increasing depth are conflicting. In regards to quadriceps activity, some studies have reported an increase in EMG activity with squat depth (29%),35 while others have not.1,5,36 Similarly, evidence related to hamstring activity also is conflicting, as studies have reported no change1,5,35 or a slight decrease in activation (absolute difference: 12% MVIC) with increasing squat depth.36 With respect to gluteus maximus, activity has been shown to increase from shallow to medium depth squatting by 65%1 but what happens thereafter is controversial. Compared to medium depth squats, gluteus maximus activity has been reported to be similar,5 or 25% greater with deep squats (28% vs. 35% MVIC).1 When comparing partial to deep squats, gluteus maximus activity has been reported to be higher with partial depths (absolute difference: 29% MVIC).36 As noted above, failure to account for trunk and tibia position with deep squatting likely underlies the inconsistent findings among studies.

From a joint motion standpoint, the primary limitation to deep squatting is the amount of available hip flexion. When end range of hip flexion is reached during squatting, a posterior pelvic tilt will occur (Figure 4). The posterior rotation of the pelvis is the result of the femur compressing into the acetabulum.37 Given that posterior pelvic tilt is coupled with lumbar spine flexion,37,38 compressive and shear forces occur at the lumbar spine.14,15,39 The fact that lumbar erector spinae activity does not increase beyond 90° of knee flexion,36 suggests that passive structures (i.e., posterior longitudinal ligament) provide the resistance to the spine flexion moment.

198465 Figure 4. Squatting to a depth that exceeds available hip flexion results in a posterior pelvic tilt.

KNEE VS. HIP EXTENSOR BIASED SQUATTING

As noted above, inclination of the trunk and tibia have opposite effects on the knee flexion moments and therefore the demand on the quadriceps. Forward inclination of the tibia increases the knee flexion moment, while forward trunk inclination decreases the knee flexion moment. As such, considering the degree of tibia inclination without considering the degree of trunk inclination can result in erroneous interpretation of the biomechanical demand at the knee. For example, the increase in the knee flexion moment resulting from inclination of the tibia could be offset by forward inclination of the trunk.10 Therefore, the relationship between trunk and tibia inclination may be a better way to characterize the biomechanical demands of the knee extensors during squatting.

Evidence in support of this premise is provided by Barrack et al., who demonstrated that the relative demand of the hip and knee extensors during squatting could be predicted based on the relative inclination of the trunk and tibia.11 Specifically, the authors reported that the difference between sagittal plane inclination of the trunk and sagittal plane inclination of the tibia (i.e., trunk-tibia angle) at peak knee flexion was predictive of the average hip/knee flexion moment ratio during the decent phase of squatting. The regression model indicated that a trunk-tibia angle of -8° resulted in a hip/knee flexion moment ratio equal to 1.0.11 When the degree of trunk inclination exceeded the degree of tibia inclination (i.e., trunk-tibia angle > 0), a hip extensor bias squat was observed (i.e., hip/knee flexion moment ratio > 1.0). Conversely, when tibia inclination exceeded trunk inclination (by at least 8°), the squat became knee extensor biased (i.e., hip/knee flexion moment ratio < 1.0).11

Based on the findings of Barrack et al., it is possible to characterize the relative demand of the hip and knee extensors using the trunk-tibia inclination difference.11 When the degree of trunk inclination exceeds the degree of tibia inclination by 10°, a hip extensor bias can be inferred (Figure 5A). When the degree of tibia inclination exceeds the degree of trunk inclination by 10°, a knee extensor bias squat can be inferred (Figure 5B). In situations where the degree of trunk and tibia inclination are within 10° or each other, the relative demands on the hip and knee extensors can be considered equal (i.e., neutral bias) (Figure 5C).

198466 Figure 5. Trunk-tibia angle (bottom left).

Hip extensor bias with trunk-tibia angle > 10°; (B) Knee extensor bias with trunk-tibia angle < -10°; (C) Neutral bias with -10° ≤ trunk-tibia angle ≤ 10°.

The orientation of the trunk relative to the tibia (and therefore the hip/knee flexion moment ratio) can be influenced by the location of the applied load. For example, when the load is placed anteriorly (i.e., barbell front squat or goblet squat), the trunk is typically held in a more upright position. Conversely, a traditional barbell back squat typically is performed with greater trunk flexion.4,40 Therefore, it is not surprising that studies have reported differing muscular demands during these squat types. Back squats are associated with higher hip flexion moments, whereas front squats exhibit higher knee flexion moments, assuming the same absolute load.40

CLINICAL APPLICATIONS

When prescribing the squat as a therapeutic exercise, the desired clinical outcome needs to be considered. For example, knee extensor bias squatting may be indicated for patients with quadriceps weakness. In contrast, performing the squat with a hip extensor bias may be preferred if the goal is to the increase strength of the hip musculature. Based on the literature reviewed above, recommendations for performing the squat exercise for various clinical conditions are presented below (Table 1).

198467 Table 1. Summary of Squat Parameters for Clinical Conditions

Patellofemoral pain	Avoid deep squats (limits patellofemoral joint stress)

Outward toe rotation (decreases knee valgus moment)

Acute Phase (hip bias)

Trunk-Tibia angle >10°

Wider stance

External band resistance around thighs

Sub-Acute Phase (progress to neutral and/or knee bias squat)

-10° <= Trunk-Tibia angle <= 10° (neutral bias) OR Trunk-Tibia angle < -10° (knee bias)

Narrow/medium stance

	
Post Anterior Cruciate Ligament Reconstruction	Outward toe rotation (decreases knee valgus moment and knee transverse moment)

Medium stance preferred over wide (decreases knee valgus moment)

Acute Phase (hip bias)

Trunk-Tibia angle >10°

External band resistance around thighs

Avoid deep squats

Sub-Acute Phase (progress to knee bias squat)

Trunk-Tibia angle < -10°

Deeper squats

Narrow/medium stance

	
Femoroacetabular impingement	Trunk-Tibia angle >10° (hip bias)

Wider stance (hip bias)

External band resistance around thighs (hip bias)

Avoid deep squats (protects against hip impingement)

Outward toe rotation to promote hip external rotation (protects against hip impingement)

	
Low Back Pain	Minimize trunk inclination (protects against lumbar muscle strain)

Trunk-Tibia angle >10° (hip bias)

Wider stance (minimizes lumbar loading)

External band resistance around thighs (hip bias)

Avoid deep squats (facilitates neutral spine)

	
Tibiofemoral Osteoarthritis	Avoid deep squats (minimizes tibiofemoral compressive forces)

Outward toe rotation (if lateral compartment osteoarthritis)

Neutral foot (if medial compartment osteoarthritis)

Acute Phase (hip bias)

Trunk-Tibia angle >10°

Wider stance

External band resistance around thighs

Sub-Acute Phase (progress to knee bias squat)

Trunk-Tibia angle < -10°

Narrow/medium stance

	

Patellofemoral pain (PFP)

Clinical guidelines for persons with PFP advocate for hip and knee extensor strengthening.41 During the acute phase of the rehabilitation process, hip biased squats should be considered to reduce the demand on the quadriceps. This is important as quadriceps force contributes directly to patellofemoral joint reaction force and patellofemoral joint stress.42 During the sub-acute or recovery phase, squats can be progressed as tolerated to be more neutral biased or even quadriceps biased by modifying the trunk-tibia relationship.

During the acute phase, gluteus maximus activation should be emphasized as this muscle controls hip adduction and internal rotation, motions known to contribute to patellofemoral joint stress and PFP.43,44 Increased gluteus maximus activation can be achieved through the use of wider stance squats,26–29 as well as external band resistance around the thighs.45,46 However, a squat stance that exceeds 150% shoulder width may result in elevated knee valgus moments.25 During the sub-acute or recovery phase, transitioning to more narrow/medium stance squats will promote greater tibial inclination47 and a quadriceps bias. Regardless of phase, a toe out position should be considered as this will result in a decrease in the knee valgus moment.21

Another important consideration for the patient with patellofemoral pain is squat depth. Patellofemoral joint stress steadily increases from partial to medium depth squatting (0° to 90°).42 The increase in patellofemoral joint stress is the result of a steadily increasing patellofemoral joint reaction force that is more pronounced than the increase in contact area as the knee flexes.42 Generally speaking, shallow-medium depth squats should be prescribed for the patient with patellofemoral pain to minimize joint stress. Furthermore, there is evidence that shallow squats may be more desirable for gluteus maximus activation compared to deep squats.36

Post Anterior Cruciate Ligament (ACL) Reconstruction

Clinical guidelines for persons post ACL reconstruction advocate for the restoration of knee extensor strength and symmetry.48,49 Patients with patellar tendon or quadriceps tendon autografts regain quadriceps strength more slowly and are more prone to anterior knee pain.50 Thus, slow and progressive loading of the quadriceps should be the focus. For patients with donor-site pain, slower rates of loading/tempo may be better tolerated to stimulate tendon remodeling and muscular strengthening.50 Given that patients post ACL reconstruction are susceptible to anterior knee pain, hip biased squatting should be considered to lower the demand on the quadriceps using the trunk-tibia relationship recommendations above. Secondary considerations for hip bias squatting early in the recovery process include external band resistance around the thighs to promote gluteus maximus and gluteus medius activation45,46 and avoidance of deep squats (i.e., recommendations highlighted above for PFP). Medium stance squats are preferred over wide stance squats to minimize the knee valgus moment.

As tolerance to donor site loading improves, squats should be modified to progressively emphasize quadriceps loading (i.e., knee biased squatting). This can be achieved by either modifying the trunk position (more upright), promoting greater tibial inclination, or a combination of both. Secondary considerations for the introduction of more knee bias squatting include the use of deeper squats to increase quadriceps demands (moments)30,32 and narrow/medium stance widths. Regardless of squat type utilized (hip vs. knee bias), care should be taken to avoid valgus and transverse plane moments at the knee by promoting some degree of toe out.21

Femoroacetabular impingement (FAI)

FAI, or abutment or impingement of the femoral neck against the acetabular labrum, can result in chondrolabral damage, thereby contributing to early onset of hip osteoarthritis.51,52 Persons with FAI exhibit impaired mobility at the hip (specifically hip flexion) and deficits in gluteal muscle activation.51,53 As such, selecting squatting mechanics that emphasize gluteus maximus and medius activation is prudent by optimizing the trunk-tibia relationship, utilizing a wider stance, and external band resistance around the thighs (see recommendations above).

Squat depth should be limited to avoid hip flexion beyond the patient’s available range of motion. This is important as patients with FAI have limited ability to posteriorly tilt the pelvis during squatting, which places them at greater risk for impingement.54 Deep squats (even if pain free) should be avoided. Although up to 25% of patients with FAI can perform deep squats without pain,55 it is important to note that deep squats impose large amplitudes of hip joint stress56 and increase the requirements for hip flexion and hip internal rotation,54,57 the hallmark movements that contribute to impingement. A toe out stance also should be considered as this will promote a greater degree of hip external rotation and gluteal activation, thereby minimizing the potential for impingment.54,58

Low Back Pain

Hip weakness (abductors, adductors, and extensors) is a common finding in persons with low back pain.59 As such, squatting recommendations for low back pain should aim to minimize the compressive and shear loads on the lumbar spine, while simultaneously promoting adequate hip muscle activation. However, trunk inclination should be limited to avoid excessive lumbar muscle strain. To obtain a hip bias squat with limited forward trunk lean, a wider stance width can be used. A wider stance will reduce ankle dorsiflexion,47 which will facilitate a more favorable trunk-tibia relationship to produce a hip bias. Additionally, a wider stance during squatting reduces lumbar loading26 and permits a more upright lumbar (less kyphosis).60 Secondary considerations for hip bias squatting include external band resistance around the thighs to promote gluteus maximus and gluteus medius activation.45,46

Similar to what was described above for FAI, squat depth should be limited to avoid flexing the hip beyond the available range of motion, thereby limiting posterior pelvic tilt. That is, squat depth should be limited to a depth in which a neutral spine can be maintained. As noted above, posterior pelvic tilt is coupled with lumbar spine flexion,37,38 resulting in compressive and shear forces occur at the lumbar spine.14,15,39

Tibiofemoral Osteoarthritis

Osteoarthritis is the most common joint disease,61 primarily affecting the tibiofemoral joint.62,63 Lower-extremity strength deficits are common in patients with knee osteoarthritis,64 highlighting the importance of appropriate squatting for overall lower extremity strength. High compressive loads in the tibiofemoral joint can worsen osteoarthritis by increasing stress/strain on internal structures (e.g., articular cartilage and menisci).65,66 Therefore, squatting recommendations for tibiofemoral osteoarthritis should prioritize lower extremity strengthening while reducing tibiofemoral loading. Similar to PFP and ACL recommendations above, patients with tibiofemoral joint arthritis should progress from a hip bias to knee bias using the trunk-tibia relationship recommendations.

As for the tibiofemoral joint, compressive forces steadily increase when squatting from a partial to a deep position.3,67 Since tibiofemoral contact area decreases with increasing knee flexion, contact stresses also increase.68,69 Therefore, deep squats should be avoided. Additional considerations for hip bias squatting early in the rehabilitation process to improve gluteal activation include external band resistance around the thighs45,46 and a wider stance.28,29 However, tibiofemoral compressive forces during a wide squat (compared to narrow squat) are approximately 15% higher.2

Considerations for knee bias squatting later in the rehabilitation process include transitioning to more narrow/medium stance squats to promote greater tibial inclination47 and a quadriceps bias. Regardless of squat type (hip vs. knee bias), outward foot rotation may need to be limited in the presence of medial compartment osteoarthritis but advised in the presence of lateral compartment osteoarthritis. An outwardly rotated foot decreases loading in the lateral compartment (by decreasing the knee valgus moment) but increases loading in the medial compartment (by increasing the knee varus moment).21

CONCLUSION

The squat can be a safe and effective exercise if properly executed for both rehabilitation and sport performance purposes. However, selection of specific squatting parameters requires a thorough understanding of their impact on muscle activity and joint loading. The preceding review examines these factors in detail and provides evidence to guide clinical decision making. It is important for clinicians to prescribe appropriate squatting parameters based on the individual needs of the patient to maximize the effectiveness of the exercise. Additional work is necessary to establish the appropriateness and effectiveness of squat exercise for patients with various musculoskeletal conditions. While the current review summarizes important research in this area, it should be noted that comparisons across the numerous studies cited (particularly those related to EMG) should be approached with caution owing to differences in data reduction/analysis (including normalization) and how various confounding factors were controlled.

Conflicts of interest

The authors report no conflicts of interest.
==== Refs
The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles J Strength Cond Res Caterisano A. Moss R.F. Pellinger T.K.. 2002
16 3 428 32 12173958
Effects of technique variations on knee biomechanics during the squat and leg press Medicine & Science in Sports & Exercise Escamilla RAFAEL F. Fleisig GLENN S. Zheng NAIQUAN LANDER JEFFERY E. BARRENTINE STEVEN W. ANDREWS JAMES R. BERGEMANN BRIAN W. MOORMAN CLAUDE T. III Ovid Technologies (Wolters Kluwer Health) 9 2001
33 9 1552 1566 0195-9131 10.1097/00005768-200109000-00020 10.1097/00005768-200109000-00020 11528346
Knee biomechanics of the dynamic squat exercise Medicine and Science in Sports and Exercise Escamilla RAFAEL F. Ovid Technologies (Wolters Kluwer Health) 1 2001
33 1 127 141 0195-9131 10.1097/00005768-200101000-00020 10.1097/00005768-200101000-00020
Kinematic and EMG activities during front and back squat variations in maximum loads Journal of Sports Sciences Yavuz Hasan Ulas Erdağ Deniz Amca Arif Mithat Aritan Serdar Informa UK Limited 29 1 2015
33 10 1058 1066 0264-0414 10.1080/02640414.2014.984240 10.1080/02640414.2014.984240
A Comparison of Gluteus Maximus, Biceps Femoris, and Vastus Lateralis Electromyography Amplitude in the Parallel, Full, and Front Squat Variations in Resistance-Trained Females Journal of Applied Biomechanics Contreras Bret Vigotsky Andrew D. Schoenfeld Brad J. Beardsley Chris Cronin John Human Kinetics 2 2016
32 1 16 22 1065-8483 10.1123/jab.2015-0113 10.1123/jab.2015-0113
Trunk muscle activation during dynamic weight-training exercises and isometric instability activities The Journal of Strength and Conditioning Research Hamlyn Nicolle Behm David G. Young Warren B. Ovid Technologies (Wolters Kluwer Health) 2007
21 4 1108 12 1064-8011 10.1519/r-20366.1 10.1519/r-20366.1 18076231
Muscle activation and strength in squat and Bulgarian squat on stable and unstable surface International Journal of Sports Medicine Andersen V. Fimland M.S. Brennset Ø. Haslestad L. Lundteigen M. Skalleberg K. Saeterbakken A. Georg Thieme Verlag KG 25 9 2014
35 14 1196 1202 0172-4622 10.1055/s-0034-1382016 10.1055/s-0034-1382016
A biomechanical comparison of back and front squats in healthy trained individuals Journal of Strength and Conditioning Research Gullett Jonathan C Tillman Mark D Gutierrez Gregory M Chow John W Ovid Technologies (Wolters Kluwer Health) 1 2009
23 1 284 292 1064-8011 10.1519/jsc.0b013e31818546bb 10.1519/jsc.0b013e31818546bb
Modelling the joint torques and loadings during squatting at the Smith machine Journal of Sports Sciences Biscarini Andrea Benvenuti Paolo Botti Fabio Mastrandrea Francesco Zanuso Silvano Informa UK Limited 3 2011
29 5 457 469 0264-0414 10.1080/02640414.2010.534859 10.1080/02640414.2010.534859 21225486
Trunk Inclination During Squatting is a Better Predictor of the Knee-Extensor Moment Than Shank Inclination Journal of Sport Rehabilitation Straub Rachel K. Barrack Adam J. Cannon Jordan Powers Christopher M. Human Kinetics 1 8 2021
30 6 899 904 1056-6716 10.1123/jsr.2020-0397 10.1123/jsr.2020-0397
the relative orientation of the trunk and tibia can be used to estimate the demands on the hip and knee extensors during the barbell back squat International Journal of Sports Science & Coaching Barrack Adam J Straub Rachel K Cannon Jordan Powers Christopher M SAGE Publications 3 3 2021
16 4 1004 1010 1747-9541 10.1177/1747954121997957 10.1177/1747954121997957
Activation of back and lower limb muscles during squat exercises with different trunk flexion Journal of Physical Therapy Science Lee Tae-Sik Song Min-Young Kwon Yu-Jeong Society of Physical Therapy Science 2016
28 12 3407 3410 0915-5287 10.1589/jpts.28.3407 10.1589/jpts.28.3407 28174462
Analysis of lumbar spine and hip motion during forward bending in subjects with and without a history of low back pain Spine Esola Marcia A. McClure Philip W. Fitzgerald G. Kelley Siegler Sorin Ovid Technologies (Wolters Kluwer Health) 1 1996
21 1 71 78 0362-2436 10.1097/00007632-199601010-00017 10.1097/00007632-199601010-00017
The biomechanics of low back injury: implications on current practice in industry and the clinic Journal of Biomechanics McGill Stuart M. Elsevier BV 5 1997
30 5 465 475 0021-9290 10.1016/s0021-9290(96)00172-8 10.1016/s0021-9290(96)00172-8 9109558
Changes in lumbar lordosis modify the role of the extensor muscles Clinical Biomechanics McGill Stuart M Hughson Richard L Parks Kellie Elsevier BV 12 2000
15 10 777 780 0268-0033 10.1016/s0268-0033(00)00037-1 10.1016/s0268-0033(00)00037-1
Effects of anterior knee displacement during squatting on patellofemoral joint stress Journal of Sport Rehabilitation Kernozek Thomas W. Gheidi Naghmeh Zellmer Matthew Hove Jordan Heinert Becky L. Torry Michael R. Human Kinetics 1 5 2018
27 3 237 243 1056-6716 10.1123/jsr.2016-0197 10.1123/jsr.2016-0197
Effect of knee position on hip and knee torques during the barbell squat J Strength Cond Res Fry A.C. Smith J.C. Schilling B.K. 2003
17 4 629 33 14636100
Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats Journal of Strength and Conditioning Research Lorenzetti Silvio Gülay Turgut Stoop Mirjam List Renate Gerber Hans Schellenberg Florian Stüssi Edgar Ovid Technologies (Wolters Kluwer Health) 10 2012
26 10 2829 2836 1064-8011 10.1519/jsc.0b013e318267918b 10.1519/jsc.0b013e318267918b
Footwear and elevated heel influence on barbell back squat: A review Journal of Biomechanical Engineering Pangan Aaron Michael Leineweber Matthew ASME International 6 5 2021
143 9 0148-0731 10.1115/1.4050820 10.1115/1.4050820
The effect of weightlifting shoes on the kinetics and kinematics of the back squat Journal of Sports Sciences Legg Hayley S. Glaister Mark Cleather Daniel J. Goodwin Jon E. Informa UK Limited 2017
35 5 508 515 0264-0414 10.1080/02640414.2016.1175652 10.1080/02640414.2016.1175652 27096286
Alterations in three-dimensional knee kinematics and kinetics during neutral, squeeze and outward squat Journal of Human Kinetics Han Shuyang Ge Shirong Liu Hongtao Liu Rong Termedia Sp. z.o.o. 1 12 2013
39 1 59 66 1899-7562 10.2478/hukin-2013-0068 10.2478/hukin-2013-0068 24511341
Electromyographic analysis of the squat performed in self-selected lower extremity neutral rotation and 30 degrees of lower extremity turn-out from the self-selected neutral position Journal of Orthopaedic & Sports Physical Therapy Ninos Joel C. Irrgang James J. Burdett Ray Weiss Jeffery R. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 5 1997
25 5 307 315 0190-6011 10.2519/jospt.1997.25.5.307 10.2519/jospt.1997.25.5.307 9130147
The effect of knee and foot position on the electromyographical activity of the superficial quadriceps Journal of Orthopaedic & Sports Physical Therapy Signorile Joseph F. Kacsik Denise Perry Arlette Robertson Bobby Williams Richard Lowensteyn Ilka Digel Sarah Caruso John LeBlanc William G. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 7 1995
22 1 2 9 0190-6011 10.2519/jospt.1995.22.1.2 10.2519/jospt.1995.22.1.2 7550299
Influence of hip external rotation on hip adductor and rectus femoris myoelectric activity during a dynamic parallel squat Journal of Strength and Conditioning Research Pereira Glauber Ribeiro Leporace Gustavo Chagas Daniel Furtado Luis F L Praxedes Jomilto Batista Luiz A Ovid Technologies (Wolters Kluwer Health) 10 2010
24 10 2749 2754 1064-8011 10.1519/jsc.0b013e3181c6a139 10.1519/jsc.0b013e3181c6a139
Effects of barbell back squat stance width on sagittal and frontal hip and knee kinetics Scandinavian Journal of Medicine & Science in Sports Lahti Johan Hegyi András Vigotsky Andrew D. Ahtiainen Juha P. Wiley 2019
29 1 44 54 0905-7188 10.1111/sms.13305 10.1111/sms.13305
A biomechanical comparison of the traditional squat, powerlifting squat, and box squat Journal of Strength and Conditioning Research Swinton Paul A. Lloyd Ray Keogh Justin W. L. Agouris Ioannis Stewart Arthur D. Ovid Technologies (Wolters Kluwer Health) 7 2012
26 7 1805 1816 1064-8011 10.1519/jsc.0b013e3182577067 10.1519/jsc.0b013e3182577067 22505136
A three-dimensional biomechanical analysis of the squat during varying stance widths Medicine and Science in Sports and Exercise Escamilla RAFAEL F. Fleisig GLENN S. Lowry TRACY M. Barrentine STEVEN W. Andrews JAMES R. Ovid Technologies (Wolters Kluwer Health) 6 2001
33 6 984 998 0195-9131 10.1097/00005768-200106000-00019 10.1097/00005768-200106000-00019 11404665
Stance width and bar load effects on leg muscle activity during the parallel squat Medicine & Science in Sports & Exercise McCaw STEVEN T. Melrose DONALD R. Ovid Technologies (Wolters Kluwer Health) 3 1999
31 3 428 436 0195-9131 10.1097/00005768-199903000-00012 10.1097/00005768-199903000-00012 10188748
The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads Journal of Strength and Conditioning Research Paoli Antonio Marcolin Giuseppe Petrone Nicola Ovid Technologies (Wolters Kluwer Health) 1 2009
23 1 246 250 1064-8011 10.1519/jsc.0b013e3181876811 10.1519/jsc.0b013e3181876811
Knee joint kinetics in relation to commonly prescribed squat loads and depths Journal of Strength and Conditioning Research Cotter Joshua A. Chaudhari Ajit M. Jamison Steve T. Devor Steven T. Ovid Technologies (Wolters Kluwer Health) 7 2013
27 7 1765 1774 1064-8011 10.1519/jsc.0b013e3182773319 10.1519/jsc.0b013e3182773319 23085977
Patellofemoral joint kinetics while squatting with and without an external load Journal of Orthopaedic & Sports Physical Therapy Wallace David A. Salem George J. Salinas Ruben Powers Christopher M. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 4 2002
32 4 141 148 0190-6011 10.2519/jospt.2002.32.4.141 10.2519/jospt.2002.32.4.141 11949662
Effect of squat depth and barbell load on relative muscular effort in squatting Journal of Strength and Conditioning Research Bryanton Megan A. Kennedy Michael D. Carey Jason P. Chiu Loren Z.F. Ovid Technologies (Wolters Kluwer Health) 10 2012
26 10 2820 2828 1064-8011 10.1519/jsc.0b013e31826791a7 10.1519/jsc.0b013e31826791a7
Patellofemoral joint kinetics in females when using different depths and loads during the barbell back squat European Journal of Sport Science Zavala Linnea Flores Victoria Cotter Joshua A. Becker James Wiley 2021
21 7 976 984 1746-1391 10.1080/17461391.2020.1806935 10.1080/17461391.2020.1806935 32781938
Patellofemoral joint kinetics during squatting in collegiate women athletes Clinical Biomechanics Salem George J. Powers Christopher M. Elsevier BV 6 2001
16 5 424 430 0268-0033 10.1016/s0268-0033(01)00017-1 10.1016/s0268-0033(01)00017-1 11390050
The effect of squat depth on multiarticular muscle activation in collegiate cross-country runners Journal of Strength and Conditioning Research Gorsuch Joshua Long Janey Miller Katie Primeau Kyle Rutledge Sarah Sossong Andrew Durocher John J. Ovid Technologies (Wolters Kluwer Health) 9 2013
27 9 2619 2625 1064-8011 10.1519/jsc.0b013e31828055d5 10.1519/jsc.0b013e31828055d5 23254544
Muscle activation differs between partial and full back squat exercise with external load equated Journal of Strength and Conditioning Research da Silva Josinaldo J. Schoenfeld Brad J. Marchetti Priscyla N. Pecoraro Silvio L. Greve Julia M.D. Marchetti Paulo H. Ovid Technologies (Wolters Kluwer Health) 6 2017
31 6 1688 1693 1064-8011 10.1519/jsc.0000000000001713 10.1519/jsc.0000000000001713 28538321
Hip flexion angles during supine range of motion and bodyweight squats Int J Exerc Sci Mata A.J. Hayashi H. Moreno P.A. Dudley R.I. Sorenson E.A. 2021
14 1 912 918 34567352
The geometric curvature of the lumbar spine during restricted and unrestricted squats J Sports Med Phys Fitness Campos M.H. Alaman L.I. Seffrin-Neto A.A. Vieira C.A. MC D.E.P. CA D.E.L. 2016
57 6 773 781 27015103
An electromyographic analysis of two techniques for squat lifting and lowering Physical Therapy Delitto Ronna S Rose Steven J Oxford University Press (OUP) 1 6 1992
72 6 438 448 0031-9023 10.1093/ptj/72.6.438 10.1093/ptj/72.6.438
Load-dependent mechanical demands of the lower extremity during the back and front squat Journal of Sports Sciences Krzyszkowski John Kipp Kristof Informa UK Limited 16 6 2020
38 17 2005 2012 0264-0414 10.1080/02640414.2020.1766738 10.1080/02640414.2020.1766738
A systematic review of clinical practice guidelines for physical therapist management of patellofemoral pain Physical Therapy Wallis Jason A Roddy Leanne Bottrell Judy Parslow Sue Taylor Nicholas F Oxford University Press (OUP) 3 2 2021
101 3 0031-9023 10.1093/ptj/pzab021 10.1093/ptj/pzab021
Patellofemoral joint stress during weight bearing and non-weight bearing quadriceps exercises Journal of Orthopaedic & Sports Physical Therapy Powers Christopher M. Ho Kai-Yu Chen Yu-Jen Souza Richard B. Farrokhi Shawn Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 5 2014
44 5 320 327 0190-6011 10.2519/jospt.2014.4936 10.2519/jospt.2014.4936 24673446
Femur rotation increases patella cartilage stress in females with patellofemoral pain Medicine & Science in Sports & Exercise Liao TZU-CHIEH Yang NICHOLAS Ho KAI-YU Farrokhi SHAWN Powers CHRISTOPHER M. Ovid Technologies (Wolters Kluwer Health) 9 2015
47 9 1775 1780 0195-9131 10.1249/mss.0000000000000617 10.1249/mss.0000000000000617 25606814
Hip and knee kinematics are associated with pain and self-reported functional status in males and females with patellofemoral pain International Journal of Sports Medicine Nakagawa T.H. Serrão F.V. Maciel C.D. Powers C.M. Georg Thieme Verlag KG 14 6 2013
34 11 997 1002 0172-4622 10.1055/s-0033-1334966 10.1055/s-0033-1334966
Effects of a band loop on lower extremity muscle activity and kinematics during the barbell squat Int J Sports Phys Ther Foley R.C.A. Bulbrook B.D. Button D.C. Holmes M.W.R. 2017
12 4 550 559 28900561
Looped elastic resistance during squats: How do band position and stiffness affect hip myoelectric activity? Journal of Functional Morphology and Kinesiology Martins Eduardo C. Steffen Lucas B. Gomes Diogo Herzog Walter Haupenthal Alessandro de Brito Fontana Heiliane MDPI AG 19 8 2022
7 3 60 2411-5142 10.3390/jfmk7030060 10.3390/jfmk7030060 35997376
The Effect of stance width and anthropometrics on joint range of motion in the lower extremities during a back squat Int J Exerc Sci Demers E. Pendenza J. Radevich V. Preuss R. 2018
11 1 764 775 29997725
How should clinicians rehabilitate patients after ACL reconstruction? A systematic review of clinical practice guidelines (CPGs) with a focus on quality appraisal (AGREE II) British Journal of Sports Medicine Andrade Renato Pereira Rogério van Cingel Robert Staal J Bart Espregueira-Mendes João BMJ 2020
54 9 512 519 0306-3674 10.1136/bjsports-2018-100310 10.1136/bjsports-2018-100310 31175108
Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction British Journal of Sports Medicine Kotsifaki Roula Korakakis Vasileios King Enda Barbosa Olivia Maree Dustin Pantouveris Michail Bjerregaard Andreas Luomajoki Julius Wilhelmsen Jan Whiteley Rodney BMJ 2 2 2023
57 9 500 514 0306-3674 10.1136/bjsports-2022-106158 10.1136/bjsports-2022-106158
ACL Reconstruction rehabilitation: Clinical data, biologic healing, and criterion-based milestones to inform a return-to-sport guideline Sports Health: A Multidisciplinary Approach Brinlee Alexander W. Dickenson Scott B. Hunter-Giordano Airelle Snyder-Mackler Lynn SAGE Publications 2022
14 5 770 779 1941-7381 10.1177/19417381211056873 10.1177/19417381211056873 34903114
A review of femoroacetabular impingement in athletes Sports Medicine Keogh Michael J. Batt Mark E. Springer Science and Business Media LLC 2008
38 10 863 878 0112-1642 10.2165/00007256-200838100-00005 10.2165/00007256-200838100-00005 18803437
The etiology of osteoarthritis of the hip: an integrated mechanical concept Clinical Orthopaedics & Related Research Ganz Reinhold Leunig Michael Leunig-Ganz Katharina Harris William H. Ovid Technologies (Wolters Kluwer Health) 2 2008
466 2 264 272 0009-921X 10.1007/s11999-007-0060-z 10.1007/s11999-007-0060-z 18196405
What is femoroacetabular impingement? British Journal of Sports Medicine Agricola R Weinans H BMJ 2016
50 4 196 197 0306-3674 10.1136/bjsports-2015-094766 10.1136/bjsports-2015-094766 26130699
Hip kinematics and kinetics in persons with and without cam femoroacetabular impingement during a deep squat task Clinical Biomechanics Bagwell Jennifer J. Snibbe Jason Gerhardt Michael Powers Christopher M. Elsevier BV 1 2016
31 87 92 0268-0033 10.1016/j.clinbiomech.2015.09.016 10.1016/j.clinbiomech.2015.09.016
A painful squat test provides limited diagnostic utility in CAM-type femoroacetabular impingement Knee Surgery, Sports Traumatology, Arthroscopy Ayeni Olufemi Chu Raymond Hetaimish Bandar Nur Liin Simunovic Nicole Farrokhyar Forough Bedi Asheesh Bhandari Mohit Wiley 2014
22 4 806 811 0942-2056 10.1007/s00167-013-2668-8 10.1007/s00167-013-2668-8
Hip joint stresses due to cam-type femoroacetabular impingement: A systematic review of finite element simulations PLoS One Ng K. C. Geoffrey Lamontagne Mario Labrosse Michel R. Beaulé Paul E. Public Library of Science (PLoS) 26 1 2016
11 1 e0147813 1932-6203 10.1371/journal.pone.0147813 10.1371/journal.pone.0147813 26812602
Variation of rotation moment arms with hip flexion Journal of Biomechanics Delp Scott L Hess William E Hungerford David S Jones Lynne C Elsevier BV 5 1999
32 5 493 501 0021-9290 10.1016/s0021-9290(99)00032-9 10.1016/s0021-9290(99)00032-9 10327003
The influence of squat kinematics and cam morphology on acetabular stress Arthroscopy: The Journal of Arthroscopic & Related Surgery Bagwell Jennifer J. Powers Christopher M. Elsevier BV 10 2017
33 10 1797 1803 0749-8063 10.1016/j.arthro.2017.03.018 10.1016/j.arthro.2017.03.018
Is there hip muscle weakness in adults with chronic non-specific low back pain? A cross-sectional study BMC Musculoskeletal Disorders Pizol Gustavo Zanotti Ferro Moura Franco Katherinne Cristiane Miyamoto Gisela Maria Nunes Cabral Cristina Springer Science and Business Media LLC 7 10 2023
24 1 798 1471-2474 10.1186/s12891-023-06920-x 10.1186/s12891-023-06920-x 37805476
The lumbar and sacrum movement pattern during the back squat exercise Journal of Strength and Conditioning Research McKean Mark R Dunn Peter K Burkett Brendan J. Ovid Technologies (Wolters Kluwer Health) 10 2010
24 10 2731 2741 1064-8011 10.1519/jsc.0b013e3181e2e166 10.1519/jsc.0b013e3181e2e166
Epidemiology of osteoarthritis Orthopedics D'Ambrosia R.D. 2005
28 2 Suppl S201 205 15747607
The incidence and natural history of knee osteoarthritis in the elderly. The Framingham Osteoarthritis Study Arthritis & Rheumatism Felson David T. Zhang Yuqing Hannan Marian T. Naimark Allan Weissman Barbara N. Aliabadi Piran Levy Daniel Wiley 10 1995
38 10 1500 1505 0004-3591 10.1002/art.1780381017 10.1002/art.1780381017
Association of squatting with increased prevalence of radiographic tibiofemoral knee osteoarthritis: the Beijing Osteoarthritis Study Arthritis & Rheumatism Zhang Yuqing Hunter David J. Nevitt Michael C. Xu Ling Niu Jingbo Lui Li-Yung Yu Wei Aliabadi Piran Felson David T. Wiley 4 2004
50 4 1187 1192 0004-3591 10.1002/art.20127 10.1002/art.20127 15077301
Muscle impairments in patients with knee osteoarthritis Sports Health: A Multidisciplinary Approach Alnahdi Ali H. Zeni Joseph A. Snyder-Mackler Lynn SAGE Publications 19 6 2012
4 4 284 292 1941-7381 10.1177/1941738112445726 10.1177/1941738112445726 23016099
The role of the meniscus in knee osteoarthritis: a cause or consequence? Radiologic Clinics of North America Englund Martin Guermazi Ali Lohmander Stefan L. Elsevier BV 7 2009
47 4 703 712 0033-8389 10.1016/j.rcl.2009.03.003 10.1016/j.rcl.2009.03.003 19631077
How severe must repetitive loading be to kill chondrocytes in articular cartilage? Osteoarthritis and Cartilage Clements K.M. Bee Z.C. Crossingham G.V. Adams M.A. Sharif M. Elsevier BV 7 2001
9 5 499 507 1063-4584 10.1053/joca.2000.0417 10.1053/joca.2000.0417 11467899
Joint load during the parallel squat in powerlifting and force analysis of in vivo bilateral quadriceps tendon rupture Scand J Sports Sci Nisell R. 1986
8 63 70
Femorotibial weight-bearing areas. Experimental determination The Journal of Bone & Joint Surgery Maquet P G Van de Berg A J Simonet J C Ovid Technologies (Wolters Kluwer Health) 9 1975
57 6 766 771 0021-9355 10.2106/00004623-197557060-00005 10.2106/00004623-197557060-00005 1158911
Tibiofemoral joint contact force in deep knee flexion and its consideration in knee osteoarthritis and joint replacement Journal of Applied Biomechanics Nagura Takeo Matsumoto Hideo Kiriyama Yoshimori Chaudhari Ajit Andriacchi Thomas P. Human Kinetics 11 2006
22 4 305 313 1065-8483 10.1123/jab.22.4.305 10.1123/jab.22.4.305
