JSIMD Journal

Keywords: Squat Variations; Front Squat; High-Bar Back Squat; Low-Bar Back Squat; Barbell Squat.

Introduction

The squat is generally regarded as a valid and reliable measure of lower body/core strength and functional power. Furthermore, it is considered a standard exercise for increasing lower extremity maximum strength [1-3]. It has therefore found its way into many areas of strength and conditioning training and is indispensable in most sports due to its versatility and functionality [4]. For athletes who perform running, sprinting or jumping movements, the squat is particularly relevant because it trains the most important muscle groups (m. rectus femoris, m. gluteus maximus, m. biceps femoris, m. semitendinosus, m. triceps sure) required for these movements [5,6]. Moreover, due to its biomechanical and neuromuscular characteristics that are similar to a wide variety of athletic movements, the squat is incorporated into numerous routines designed to improve athletic performance [7-10]. There are a total of three basic bilateral squat variations where a barbell is placed on the shoulders: the High-Bar Back-Squat (HBBS), the Low-Bar Back-Squat (LBBS) and the front squat (FS). Research into the biomechanics and/or kinematics of the classic bilateral barbell squat has mainly focused on the HBBS [11-31]. Fewer scientific publications examine the differences between HBBSs and LBBSs [32-44]. There is only a limited number of

published studies on the biomechanical and/or kinematic differences between the HBBS and the FS [45-54] that showed contradictory results regarding net joint moments and muscle activity [53]. In addition, to the best knowledge of the author, no scientific publication to date is exclusively devoted to comparing LBBSs and FSs. Only one study by Fry et al. [55] investigated the kinematic differences between all three variations within a single study, and another investigation examined the kinematic differences of FS and back squats, yet allowing the subjects to freely choose between the HBBS and LBBS [51]. The following review summarizes the findings of all relevant studies detected which address the differences between FSs, HBBSs, and LBBSs, thereby allowing practitioners, trainers, therapists, and athletes to choose the variation most appropriate for achieving their respective goals.

Material and Methods

The research strategy was designed to include all possible indexed articles referring to the differences and similarities between the HBBS, LBBS and FS. Online databases providing extensive scientific literature of sport scientific and sport medical research, including PubMed, SPORTD iscus and Google Scholar, were screened for referenced articles from their publication date until May 2023. All databases were independently searched and vetted with the following string of search terms: “squat AND biomechanics”, “squat AND kinematics” “squat variations AND biomechanics”, “squat variations AND kinematics”, “front squat”, “high-bar squat”, “high-bar back squat”, “low-bar squat”, “lowbar back squat”, and “squat variations” and reviewed for inclusion. Only peer-reviewed German and English studies on bilateral barbell squat variations using the classic barbell were included in the review. All studies unrelated to bilateral barbell squat variations with the classic barbell, such as safety-bar squats, were excluded. The relevant information for differentiating and analyzing HBBSs, LBBSs and FSs was extracted from the included studies and comprehensively summarized.

Results

HBBS:

There are significant kinematic, kinetic and biomechanical differences between the three basic variations of the barbell squat [34,55]. The most common variation of the barbell squat is the HBBS, also known as traditional squat or Olympic squat [37]. When performing a HBBS, the barbell is placed on the upper part of the trapezius muscle directly under the spinous process of the 7th cervical vertebra (C7) [33]. It is considered a compromise between the hip-dominant LBBS (Figure 1, left) and the kneeextensor dominant FS (Figure 1, right) [56]. Different barbell positionings manifest in a shifted center of mass [34]. As a result, the movement patterns are adapted to ensure that the center of mass stays within the base of support while performing different squatting movements in order to maintain stability (Swinton et al., 2012). The more anteriorly the weight is positioned, the more erect the upper body can be during a squat [55,56], which consequently affects the moment arm ratio between the hip and knee joints (Figure 1, M1 and M2). From a kinematic point of view, the HBBS presents a balanced variation with a trunk segment (TSA) angle of 46.3 ± 4.8 as compared to the FS (with a more upright upper body (TSA: 63.6 ± 4.2) and the LBBS (with a more forwardly inclined torso (TSA of 40.7 ± 5. 8) [55]. The HBBS also requires less ankledorsiflexion than the FS at the same squatting depth, which is a relevant benefit for many athletes [56]. Therefore, the HBBS is usually the first variation to master after learning the bodyweight squat and before practicing its derivatives [4]. Even though LBBSs typically permit athletes to lift heavier weights, the HBBS remains one of the most essential exercises in athlete training [41], as it is characterized by an increased amount of knee flexion, a decreased amount of hip flexion, a more upright torso, and a deeper squatting position compared to HBBSs [37,44,57]. Moreover, deep HBBSs are an efficient exercise for preventing injuries and strengthening the lower extremities, provided that a proper technique is learned under the supervision of a professional [57]. Contrary to widespread belief, deep barbell squats do not increase the risk of injury of passive tissues [57]. Furthermore, recent research suggests that including deep squats to a preventative training program may be advantageous for reducing deficits prevalent among females and lowering the injury incidence [58].

LBBS:

During the LBBS the barbell is placed slightly lower on the rear deltoid in comparison to the HBBS (Figure 1, left). This also causes the elbows to rotate further back, although they remain in close proximity to the barbell’s plane of motion [42]. The LBBS is typically performed by powerlifters and particularly recommended when the primary objective is to lift as much weight as possible [39]. By situating the barbell lower on the back, the LBBS

Reduces the moment arm in key anatomical compartments and leads to improved biomechanical working conditions for the hip extensor muscles, ultimately permitting the use of heavier weights during the squat [33,37,42]. As a result of the greater upper body tilt, the torque in the hip joint (Figure 1, left, moment arm 2) and the muscle activation of the hip extensor muscles increase as compared to the other barbell variations [20,34,41]. Moreover, LBBSs are characterized by increased hip flexion and, thus, allow for a greater forward inclination of the upper body [44,37,57,55]. Because of this, the LBBS seems to be the most effective variation if the goal is to squat a maximum load, as it is the case in powerlifting competitions [33,39,42,59]. Furthermore, if the objective is to primarily strengthen the posterior-chain hip muscles involving the hamstring, gluteal and erector spinae muscle groups, LBBSs are the most recommended barbell squat variation [37].

Figure 1: LBBS, HBBS and FS The knee moment arm (M1) to hip moment arm (M2) ratio is influenced by the barbell placement.

Edited with friendly permission of the Aasgaard Company [69].

FS:

The FS is the third variation of the classic bilateral barbell squat. In contrast to the other variations, the barbell is not placed on the back but at the front of the shoulders (deltoid muscle) (Figure 1, right). Due to this barbell position, the FS requires a more upright upper body position, a greater TSA [37,53,55] (Figure 1, right) and it activates the knee extensor muscles more than the HBBS [37]. Due to the more upright body position [46,47], the increased anterior knee displacement and the consequently higher external torque in the knee joint (Figure 1, right, moment arm 1) [56], the FS is a very knee extensor dominant variation that activates the knee extensors more than the HBBS [56]. The m. quadriceps femoris muscle is therefore more activated than in other squatting variations [49,60]. However, there are several studies that indicate similar knee extensor demands, muscle activation and kinematics of the FS and HBBS [45,46,48,51,53,54]. This can be explained by varying loads as well as a comparatively small difference in load placements between the HBBS and FS, allowing individuals to modify their postures in order to put comparable external loads on their lower body [53]. Moreover, a comparison of the FS and HBBS load-velocity profiles revealed no distinctions between the two variations [52]. Although less absolute and relative load can be used in the FS than in back squat variations [2,48,61,62], recent research suggests that the FS can achieve a similar stimulus as the HBBS in terms of muscle activity, strength development and hypertrophy [48,63]. Moreover, the FS should be a foundational exercise for Olympic weightlifters since it trains the body position for the catch in the FS, which is a performance-critical factor when performing the clean [64,65].

The FS allows for a deeper squatting position and requires an increased knee flexion, less hip flexion and a more erect torso as compared to the HBBS and LBBS [56]. This may be an advantage compared to the LBBS, where there is less knee flexion [33]. This is because deep squat variations like the deep HBBS and the deep FS offer multiple benefits including greater muscle activation and increased athletic performance [66-68]. Therefore, it might be advisable to include a squat variation which can be performed to full knee flexion, such as the deep FS or deep HBBS, into the training routine.

Discussion

The purpose of this study was to review the literature on the biomechanical and kinematic differences between three prominent variations of the barbell squat: the HBBS, the LBBS, and the FS. Only one study that compares the kinematic differences between the three squat variations could be identified [55]. To the best knowledge of the author, despite the popularity of the squat, no study directly compared the biomechanical differences of the

LBBS, HBBS and FS. Simple 2D models, as illustrated in Figure 1 and applied by Rippetoe & Kilgore [69], can serve as an initial guide in order to understand the kinematics and biomechanics of different squat variations and deliver comparable results to 3D motion capture when assessing lower extremity movement [70]. However, 3D movement analysis is regarded as the gold standard for motion capture and analyzing kinematics [71]. Further research comparing and analyzing the biomechanics and kinematics of the three most important bilateral barbell squat variations should be conducted to enhance the understanding of their respective effects on muscle activation, joint loading, and overall performance. Above all, a study which compares the biomechanics of all three variations as well as a study which exclusively compares the LBBSs to the FSs are still lacking. Fry et al. [55] analyzed the kinematic dimension of the squat variations and in the study of Kasovic et al. [51] only two subjects performed a LBBS. A comprehensive investigation could help to reveal more valuable insights into the optimal squat variation for specific training goals, such as muscle hypertrophy, strength development, or injury prevention. By knowing more about how to appropriately incorporate each variation, individuals can improve their muscular development as well as their strength level and enhance their performance in a variety of strength-based activities.

Conclusion

In conclusion, each barbell squat variation is characterized by a distinct positioning of the barbell, which results in different biomechanical characteristics, including muscle activation, joint torque, and body position. The HBBS, with the barbell placed on the upper trapezius muscle, offers a compromise between the hip-dominant LBBS and knee-extensor dominant FS and is a fundamental exercise and a good starting point for beginners. The LBBS, during which the barbell is positioned lower on the posterior deltoid, should be favored if maximizing weightlifting performance is the primary objective. The FS variation is different to the other techniques in that the barbell rests on the front shoulders, resulting in a more upright upper body position. This variation engages the knee extensors to a greater extent than the other variations and is essential for athletes performing the clean, because it trains the necessary body position for a successful catch.

Author Contributions

Conceptualization GI; Methodology GI; Software GI; Validation GI; Formal Analysis GI; Investigation GI; Resources GI; Data Curation GI; Writing-Original Draft Preparation GI; Writing-Review and Editing; Visualization GI; Supervision GI; Project Administration GI; The Author has Read and Agreed to the Published Version of the Manuscript.

References

1. Sleivert G, Taingahue M (2004) The relationship between maximal jump-squat power and sprint acceleration in athletes. Eur J Appl Physiol 91: 46-52.
2. Wisløff U, Castagna C, Helgerud J, Jones R, Hoff J et al. (2004) Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players. Br J Sports Med 38: 285-288.
3. Comfort P, Stewart A, Bloom L, Clarkson B (2014) Relationships between strength, sprint, and jump performance in well-trained youth soccer players. J Strength Cond Res 28: 173-177.
4. Myer GD, Kushner AM, Brent JL, Schoenfeld BJ, Hugentobler J, et al. (2014) The back squat: A proposed assessment of functional deficits and technical factors that limit performance. Strength Cond J 36: 4-27.
5. Maddigan ME, Button DC, Behm DG (2014) Lower-limb and trunk muscle activation with back squats and weighted sled apparatus. J Strength Cond Res 28: 3346-3353.
6. da Silva JJ, Schoenfeld BJ, Marchetti PN, Pecoraro SL, Grave JMD et al. (2017) Muscle Activation Differs Between Partial and Full Back Squat Exercise with External Load Equated. J Strength Cond Res 31: 1688-1693.
7. Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk KE et al. (1998) Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc 30: 556-569.
8. Senter C, Hame SL (2006) Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury. Sports Med 36: 635-641.
9. Dunn B, Klein B, Kroll T, McLaughlin P, O’Shea et al. (1984) Coaches round table: The squat and its application to athletic performance. National Strength and Conditioning Association Journal 6: 10-23.
10. Cotter JA, Chaudhari AM, Jamison ST, Devor ST (2013) Knee joint kinetics in relation to commonly prescribed squat loads and depths. J Strength Cond Res 27: 1765-1774.
11. Escamilla RF, Fleisig GS, Zheng N, Lander JE, Barren tine SW et al. (2001) Effects of technique variations on knee biomechanics during the squat and leg press. Med Sci Sports Exerc 33:1552-1566.
12. Escamilla RF (2001) Knee biomechanics of the dynamic squat exercise. Med Sci Sports Exerc 33: 127-141.
13. Fry AC, Smith JC, Schilling BK (2003) Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res 17: 629-633.
14. Flanagan SP, Salem GJ (2007) Bilateral differences in the net joint torques during the squat exercise. J Strength Cond Res 21: 12201226.
15. Walsh JC, Quinlan JF, Stapleton R, Fitzpatrick DP, McCormack D et al. (2007) Three-dimensional motion analysis of the lumbar spine during “free squat” weight lift training. Am J Sports Med 35: 927-932.
16. Paoli A, Marcolin G, Petrone N (2009) The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. J Strength Cond Res 23: 246-250.
17. McKean MR, Dunn PK, Burkett BJ (2010) The lumbar and sacrum movement pattern during the back-squat exercise. J Strength Cond Res 24: 2731-2741.
18. Lorenzetti S, Gülay T, Stoop M, List R, Gerber H et al. (2012) Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats. J Strength Cond Res 26: 2829-2836.
19. List R, Gülay T, Stoop M, Lorenzetti S (2013) Kinematics of the trunk and the lower extremities during restricted and unrestricted squats. J Strength Cond Res 27: 1529-1538.
20. Schoenfeld BJ (2010) Squatting kinematics and kinetics and their application to exercise performance. J Strength Cond Res 24: 34973506.
21. Sinclair J, McCarthy D, Bentley I, Hurst HT, Atkins S (2015) The influence of different footwear on 3-D kinematics and muscle activation during the barbell back squat in males. Eur J Sport Sci 15: 583-590.
22. Sato K, Fortenbaugh D, Hydock DS (2012) Kinematic changes using weightlifting shoes on barbell back squat. J Strength Cond Res 26: 28-33.
23. van den Tillaar R (2015) Kinematics and muscle activation around the sticking region in free-weight barbell back squats. Kinesiologic Slovenian 21: 15-25.
24. Sato K, Fortenbaugh D, Haydock DS, Heise GD (2013) Comparison of back squat kinematics between barefoot and shoe conditions. International Journal of Sports Science & Coaching 8: 571- 578.
25. Whitting JW, Meir RA, Crowley-McHattan ZJ, Holding RC (2016) Influence of footwear type on barbell back squat using 50, 70, and 90% of one repetition maximum: A biomechanical analysis. J Strength Cond Res 30: 1085-1092.
26. Charlton JM, Hammond CA, Cochrane CK, Hatfield GL, Hunt MA et al. (2017) The Effects of a Heel Wedge on Hip, Pelvis and Trunk Biomechanics During Squatting in Resistance Trained Individuals. J Strength Cond Res 31: 1678-1687.
27. Foley RCA, Bulbrook BD, Button DC, Holmes MWR (2017) EFFECTS OF A BAND LOOP ON LOWER EXTREMITY MUSCLE ACTIVITY AND KINEMATICS DURING THE BARBELL SQUAT. Int J Sports Phys Ther 12: 550-559.
28. Sayers MGL, Bachem C, Schütz P, Taylor WR, List R et al. (2020) The effect of elevating the heels on spinal kinematics and kinetics during the back squat in trained and novice weight trainers. J Sports Sci 38: 1000-1008.
29. Choe KH, Coburn JW, Costa PB, Pamukoff DN (2021) Hip and Knee Kinetics During a Back Squat and Deadlift. J Strength Cond Res 35: 1364-1371.
30. Maddox EU, Bennett HJ (2021) Effects of External Load on Sagittal and Frontal Plane Lower Extremity Biomechanics During Back Squats. J Biomech Eng 143: 051006.
31. Larsen S, Kristiansen E, Nygaard Falch H, Estifanos Haugen M, Fimland MS et al. (2022) Effects of barbell load on kinematics, kinetics, and myoelectric activity in back squats. Sports Biomech 1-15.
32. Benz R (1989) A Kinematic Analysis of the High and Low Bar Squat Techniques by Experienced Low Bar Weight Lifters. West Chester, PA: West Chester University.
33. Wretenberg P, Feng Y, Arborelius UP (1996) High- and low-bar squatting techniques during weight-training. Med Sci Sports Exerc 28: 218-224.
34. Swinton PA, Lloyd R, Keogh JW, Agouris I, Stewart AD et al. (2012) A biomechanical comparison of the traditional squat, powerlifting squat, and box squat. J Strength Cond Res 26: 1805-1816.
35. Logar J, Kleva M, Marušič U, Supej M, Gerževič M et al. (2014) Differences in the knee torque between high-and low-bar back squat techniques: A pilot study. Annales Kinesiologiae 5.
36. Goodin J (2015) Comparison of External Kinetic and Kinematic Variables between High Barbell Back Squats and Low Barbell Back Squats across a Range of Loads. East Tennessee State University.
37. Glassbrook DJ, Helms ER, Brown SR, Storey AG (2017) A Review of the Biomechanical Differences Between the High-Bar and Low-Bar Back-Squat. J Strength Cond Res 31: 2618-2634.
38. Knutli TR (2018) Differences between sticking region in high-bar and low-bar, barbell back squat (Master’s thesis, Nord universitet).
39. Glassbrook DJ, Brown SR, Helms ER, Duncan S, Storey, AG et al. (2019) The high-bar and low-bar back squats: A biomechanical analysis. J Strength Cond Res 33 Suppl 1: S1-S18.
40. van den Tillaar R, Knutli TR, Larsen S (2020) The Effects of Barbell Placement on Kinematics and Muscle Activation Around the Sticking Region in Squats. Front Sports Act Living 2: 604177.
41. Murawa M, Fryzowicz A, Kabacinski J, Jurga J, Gorwa J et al. (2020) Muscle activation varies between high-bar and low-bar back squat. PeerJ 8: e9256.
42. Pham RD, Machek SB, Lorenz KA (2020) Technical aspects and applications of the low-bar back squat. Strength and conditioning journal 42: S 121-128.
43. Larsen S, Kristiansen E, Helms E, van den Tillaar R (2021) Effects of stance width and barbell placement on kinematics, kinetics, and myoelectric activity in back squats. Front Sports Act Living 3: 719013.
44. Park JH, Lee SJ, Shin HJ, Cho HY (2022) Influence of Loads and Loading Position on the Muscle Activity of the Trunk and Lower Extremity during Squat Exercise. Int J Environ Res Public Health 19: 13480.
45. Russell PJ, Phillips SJ (1989) A preliminary comparison of front and back squat exercises. Res Q Exerc Sport 60: 201-208.
46. Diggin D, O’Regan C, Whelan N, Daly S, McLoughlin V et al. (2011) A biomechanical analysis of front versus back squat: Injury implications. Portuguese Journal of Sport Sciences 11: 643-646.
47. Kim J (2014) Lower Body Kinematic Comparisons between Front and Back Squats in Response to Loads. In: BSU Master’s Theses and Projects Item 5.
48. Gullett JC, Tillman MD, Gutierrez GM, Chow JW (2009) A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res 23: 284-292.
49. Braidot AA, Brusa MH, Lestussi FE, Parera GP (2007) Biomechanics of front and back squat exercises. J Phys Conf Ser 90: 012009.
50. Yavuz HU, Erdağ D, Amca AM, Aritan S (2015) Kinematic and EMG activities during front and back squat variations in maximum loads. J Sports Sci 33: 1058-1066.
51. Kasovic J, Martin B, Fahs CA (2019) Kinematic Differences Between the Front and Back Squat and Conventional and Sumo Deadlift. J Strength Cond Res 33: 3213-3219.
52. Spitz RW, Gonzalez AM, Ghigiarelli JJ, Sell KM, Mangine GT et al. (2019) Load-Velocity Relationships of the Back vs. Front Squat Exercises in Resistance-Trained Men. J Strength Cond Res 33: 301306.
53. Goršič M, Rochelle LE, Layer JS, Smith DT, Novak D et al. (2020) Biomechanical comparisons of back and front squats with a straight bar and four squats with a transformer bar. Sports Biomech 1-16.
54. Krzyszkowski J, Kipp K (2020) Load-dependent mechanical demands of the lower extremity during the back and front squat. J Sports Sci 38: 2005-2012.
55. Fry AC, Aro TA, Bauer JA, Kraemer WJ (1993) A comparison of methods for determining kinematic properties of three barbell squat exercises. Journal of human movement studies  24: 2S 83-95.
56. Illmeier G, Rechberger JS (2023) The Limitations of Anterior Knee Displacement during Different Barbell Squat Techniques: A Comprehensive Review. J Clin Med 12: 2955.
57. Hartmann H, Wirth K, Klusemann M (2013) Analysis of the load on the knee joint and vertebral column with changes in squatting depth and weight load. Sports Med 43: 993-1008.
58. Barrett KB, Sievert ZA, Bennett HJ (2023) A Comparison of Squat Depth and Sex on Knee Kinematics and Muscle Activation. J Biomech Eng 145: 071010.
59. Kristiansen E, Larsen S, Haugen ME, Helms E, van den Tillaar R et al. (2021) A Biomechanical Comparison of the Safety-Bar, High-Bar and Low-Bar Squat around the Sticking Region among Recreationally Resistance-Trained Men and Women. Int J Environ Res Public Health 18: 8351.
60. Erdağ D, Yavuz H (2020) Evaluation of Muscle Activities During Different Squat Variations Using Electromyography Signals.
61. Baker DG, Newton RU (2008) Comparison of lower body strength, power, acceleration, speed, agility, and sprint momentum to describe and compare playing rank among professional rugby league players. J Strength Cond Res 22: 153-158.
62. McBride JM, Blow D, Kirby TJ, Haines T, Dayne AM et al. (2009) Relationship between maximal squat strength and five, ten, and fortyyard sprint times. J Strength Cond Res 23: 1633-166.
63. Contreras B, Vigotsky AD, Schoenfeld BJ, Beardsley C, Cronin J et al. (2016) A Comparison of Gluteus Maximus, Biceps Femoris, and Vastus Lateralis Electromyography Amplitude in the Parallel, Full, and Front Squat Variations in Resistance-Trained Females. J Appl Biomech 32: 16-22.
64. Duba J, Kraemer WJ, Martin GJ (2007) A 6-Step Progression Model for Teaching the Hang Power Clean. Strength and Conditioning Journal 29: 26-35.
65. Bird S, Casey S (2012) Exploring the front squat. Strength and Conditioning Journal 34: 27-33.
66. Hartmann H, Wirth K, Klusemann M, Dalic J, Matuschek C et al. (2012) Influence of squatting depth on jumping performance. J Strength Cond Res 26: 3243 -3261.
67. Caterisano A, Moss RF, Pellinger TK, Woodruff K, Lewis VC et al. (2002) The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. J Strength Cond Res 16: 428-432.
68. Weiss L, Fry A, Wood L, Relyea G, Melton C et al. (2000) Comparative effects of deep versus shallow squat and leg-press training on vertical jumping ability and related factors. Journal of strength and conditioning Research 14: 241-247.
69. Rippetoe M, Kilgore L (2007) Starting strength: basic barbell training 2nd edition Wichita Falls: Aasgaard Company.
70. Schurr SA, Marshall AN, Resch JE, Saliba SA (2017) TWODIMENSIONAL VIDEO ANALYSIS IS COMPARABLE TO 3D MOTION CAPTURE IN LOWER EXTREMITY MOVEMENT ASSESSMENT. Int J Sports Phys Ther 12: 163-172.
71. Chung PY, Ng GY (2012) Comparison between an accelerometer and a three-dimensional motion analysis system for the detection of movement. Physiotherapy 98: 256-259.