10 November 2020

The squat is one of the bread-and-butter movements of resistance training, and rightly so. Its benefits are undoubted, which is not surprising considering the positive correlation between squat performance and numerous other physical endeavours such as sprint, jump, and hurdle performance.

There is a lot of conflicting information surrounding the squat and its technical nuances and variations. With the rise of social media, everyone is now an exercise professional and adds their two cents to the discussion.

This article will break down the barbell back squat with a focus on foot angle, squat depth, and knee displacement; along with providing practical takeaways for the personal trainer and strength and conditioning coach.

What is considered optimal?

Optimal is a term which is frequently used, but means something slightly different depending on who you ask. For the purpose of this article we are going to define optimal as the technique which minimises the risk of injury while showing the greatest activation of prime movers. Performing a movement in this manner will prove optimal over long periods of time, as it will maximise physiological adaptations while ensuring the individual remains injury-free.

The barbell back squat

The barbell back squat is probably the movement you’re most familiar with. The barbell is positioned across the trapezius, and hands grip the bar with the palms facing forward. The feet are positioned in a natural stance approximately shoulder-width apart, creating a stable base of support.

Once the unrack has been completed and the athlete is in a comfortable starting position, the lift is ready to be commenced. The individual sits down, eccentric muscle contraction occurs with flexion at the hip, knee, and ankle. Optimal squat depth will be discussed later in this article, but the individual will drop down until their thighs are approximately parallel with the floor. The individual will then return to the starting position, causing concentric contraction and extension at the hip, knee, and ankle.

Anterior knee displacement

There has been a huge amount of talk regarding knee position in the squat. Previously the thought was that limiting forward knee travel and restricting the knees from travelling in front of the toes would limit the strain placed on the knee ligaments, most namely the anterior cruciate ligament (ACL) according to Beynnon et al. (1997). This thought process stemmed from the analysis of sheer and compressive forces during deep knee flexion in an open kinetic chain movement (Escamilla, 2001).

The open kinetic chain movement used was the leg extension, but during the squat (a closed kinetic chain movement) there is significantly less displacement of the tibia, which results in significantly less strain placed on the ACL (Comfort et al., 2018). This research was further supported by Escamilla et al., (2001) who examined the strain placed on the posterior cruciate ligament (PCL) during the leg extension and squat. It was found that during an isometric leg extension the forces were >4.5 x greater than body mass as opposed to only >3.5 x greater during the squat.

It is important to note that a deeper squat will result in increased forward knee travel; displacement of the knee is normal during this phase of the movement and will result in increased force placed on the ligaments and menisci (Augustsson., 1998). Decreasing the amount of forward knee travel has been shown to decrease knee torque by 22%, however limiting knee displacement has been shown to significantly increase hip torque by >1000% as well as increasing torso lean, which significantly increases torso/lumbar sheer forces (Fry et al., 2003).

Therefore it can be safely concluded that restricting forward knee travel is not optimal. The marginal decrease in force placed on the knee is significantly outweighed by the increase in force placed on the hip and lumbar spine, resulting in an increased risk of injury.

Impact of squat depth on muscle activation

This article is going to analyse these variables relating to muscle activation. The gold standard for measuring muscle activation during a dynamic movement is Electromyography (EMG). Motor neurons send electrical signals which travel throughout the body, causing muscular contraction. An EMG uses small electrodes to measure these electrical signals which is then used to monitor muscle activation (Feinberg., 2006).

The results of EMG studies have shown significant increases in the activation of the gluteus maximus during deeper range of motion squats (Caterisano et al., 2002). Activation of the vastus medialis and vastus lateralis has also been shown to increase during deeper range of motion squats. However there has been no statistical difference in the activation of the vastus intermedialis and rectus femoris with different ranges of motion (Caterisano et al., 2002).

Interestingly the back squat has relatively low levels of hamstring activation, regardless of the depth. This is contrary to popular belief. Hamstring activation only increases when there is technique breakdown, most commonly excessive forward torso lean. (Caterisano et al., 2002, Escamilla et al., 2001). Therefore, it’s important to program for additional hamstring movements to ensure adequate strengthening.

Impact of foot placement on muscle activation

Foot position has been shown to have no measurable effect on activation of any of the lower body muscles (gluteus maximus, vastus medialis, vastus lateralis, vastus lateralis, rectus femoris, semimembranosus, semitendinosus, bicep femoris). This is regardless of depth, stance width and knee travel (Escamilla et al., 2001). The only noticeable effect of increased foot rotation was increased activation of hip adductor muscles and greater external rotation at the hip joint (Rhea et al., 2016).

It is worth noting that although foot placement does not appear to effect muscle activation, it does allow increased external rotation at the hip, which for many individuals is a limiting factor in achieving a deeper squat. Therefore, it is practical for an individual to self-select a comfortable foot position which allows for a full range of motion.


It is important for a personal trainer/strength and conditioning coach to understand the practical takeaways of this information. Encouraging proper technique in the squat is essential. The athlete should self-select a comfortable foot position which allows a full range of motion, allowing natural forward knee travel. It is also essential to ensure appropriate alignment, with the knees tracking directly over the toes and avoiding any valgus knee angle.

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Augustsson, J., Esko, A., Thomeé, R., & Svantesson, U. (1998). Weight training of the thigh muscles   using closed versus open         kinetic chain exercises: a comparison of performance enhancement. Journal of Orthopaedic & Sports Physical         Therapy, 27(1), 3-8.

Beynnon, B. D., Johnson, R. J., Fleming, B. C., Stankewich, C. J., Renström, P. A., & Nichols, C. E.         (1997). The strain     behavior of the anterior cruciate ligament during squatting and active        flexion-extension: a comparison of an open              and a closed kinetic chain exercise. The American journal of sports medicine, 25(6), 823-829.

Caterisano, A., Moss, R. E., Pellinger, T. K., Woodruff, K., Lewis, V. C., Booth, W., & Khadra, T. (2002). The effect of back squat                depth on the EMG activity of 4 superficial hip and thigh muscles. The            Journal of Strength & Conditioning           Research, 16(3), 428-432.

Comfort, P., McMahon, J. J., & Suchomel, T. J. (2018). Optimizing squat technique—Revisited. Strength & Conditioning           Journal, 40(6), 68-74.

Escamilla, R. F. (2001). Knee biomechanics of the dynamic squat exercise. Medicine & science in sports & exercise, 33(1),       127-141.

Escamilla, R. F., Fleisig, G. S., Zheng, N. A. I Q. U. A. N., Lander, J. E., Barrentine, S. W., Andrews, J. R., … & Moorman III,            C. T. (2001). Effects of technique variations on knee biomechanics during the squat and leg press. Medicine &       Science in Sports &                   Exercise, 33(9), 1552-1566.

Feinberg, J. (2006). EMG: myths and facts. HSS Journal, 2(1), 19-21.

Fry, A. C., Smith, J. C., & Schilling, B. K. (2003). Effect of knee position on hip and knee torques during the barbell squat. The       Journal of Strength & Conditioning Research, 17(4), 629-633.

Rhea, M. R., Kenn, J. G., Peterson, M. D., Massey, D., Simão, R., Marin, P. J., ... & Krein, D. (2016).     Joint-angle specific strength adaptations influence improvements in power in highly trained athletes. Human movement, 17(1), 43-49.