The squat is among the most frequently used exercises in the strength and conditioning field, mainly due to its specificity to numerous athletic and functional movements. There are countless factors that can have an effect on squat kinematics; thus, in order to ensure the safety of the client or athlete it is imperative to have a thorough understanding of the squat and how it can be influenced by factors such as foot positioning, load placement, and squat depth. Let’s take a look at all three of these important components.
Squat Foot Placement
Placement of the feet during a squat can have a significant effect on squat kinetics. A wide stance has been defined in literature as slightly less to slightly greater than shoulder width, while a narrow squat has been defined as between hip and shoulder width. It has been noted that there is a significant increase in both tibiofemoral and patellofemoral compressive forces with a wide stance when compared to a narrow stance. Thus, those who wish to minimize sheer force during squats may prefer a narrow stance.
Muscle activation between stances has also been shown to vary. Although quadriceps and hamstring muscle activity has been shown to be equal in both stances, significantly more gastrocnemius muscle activation (21%) has been noted in narrow stance positions. Furthermore, greater adductor activity can be seen with a wide stance.
Lastly, extreme foot angles should be avoided during squats. Excessive inward or outward rotation can lead to altered patellar tracking and subsequent knee valgus or varus. Therefore, the knees should always track the toes during the entirety of the squat.
Position of Load
There are numerous variations of weighted squats. The three most prevalent variations are the high bar back squat (superior to acromion on upper trapezius), the low bar back squat (inferior to acromion), and the front squat (bar positioned across the clavicle resting on the anterior deltoid). Each variation is kinematically unique, thus an understanding of differences in muscle activation patterns is required.
With a high bar back squat, the bar is positioned on the upper trapezius and superior to the acromion. Once proper setup is achieved, hips and knees simultaneously flex. In order for proper stability to occur, the bar must be kept over the midline of the foot. Because of the bar placement, greater flexion of the knee in relation to hip is required in order for the bar to stay in line with the body’s center of gravity. Thus, the patellofemoral compression and ACL strain are greater during the high bar back squat when compared to the low bar back squat. This is mainly due to the increased activity in the quadriceps and decreased activity of the hip extensors.
In contrast, the low bar back squat involves bar placement inferior to the acromion. With this positioning, a greater degree of hip flexion is necessary in order for the bar to remain over the body’s center of gravity. A subsequent increase in hip extensor activity can thus be seen relative the quadriceps activity. Although patellofemoral compression and ACL strain can be reduced in this position, there is a concomitant increase in anteriorly directed torque on the torso.
Lastly, front squats vary from the back squats in that the load is placed anteriorly, with the bar resting across the clavicle with elbows elevated and forward. Due to the placement of the bar, a low degree of anterior trunk rotation is necessary to maintain the bar over the center of gravity. This enhances the action of the quadriceps, as well as reduces the torque about the hip. Additionally, a reduction in lumbar stress has been noted with the front squat when compared with both back squat variations.
The squat depth that maximizes adaptation and minimizes the risk of injury is frequently and fiercely debated. Proponents of deep squatting often assert that the increased depth helps to achieve greater muscle activation, increase adaptation, and improve athletic or functional performance. However, numerous professionals express concerns of safety, stating that the risk of injury outweighs any potential benefit.
One reason often cited for utilizing beyond parallel squatting involves increased muscular activity of particular muscles; however, conflicting explanations exist regarding the benefits of such variations in muscular activity. Some studies show a plateau in quadriceps, hamstring, and gastrocnemius activity with knee flexion angles of less than or equal to 90 degrees, with no mention of gluteus maximus activity.
On the other hand, there are other studies that concluded that although the beceps femoris does not appear to become more active as squat depth increases, the gluteus maximus becomes progressively more active as depth increases, particularly beyond parallel. Based on these findings, it seems imperative to consider the relative contribution of particular muscles when determining squat depth of a client. Furthermore, because different squat depths produce different muscular activation patterns, it may be necessary to consider specificity of training when determining squat depth.
When determining squat depth, one must consider more than muscle activation. Numerous studies have cited a potential danger that occurs during a deep squat. Despite this, the tendonous and ligamentous structures that comprise the knee appear to be more than capable of supporting loads totaling 2.5 times body weight during a deep squat. Thus, the hypothesized increased injury risk of deep squatting typically involves damage to the menisci and articulating cartilage as a result of high tibiofemoral and patellofemoral forces.
Increased patellofemoral stress from deep knee flexion exercises appears to be the primary cause for concern when determining optimal squat range of motion for a particular client. Because patellofemoral compressive force increases with greater knee flexion, clients with a history of patellofemoral dysfunction may experience optimal benefit from training within a more functional knee angle of between 0 and 50 degrees. Furthermore, deep knee squatting appears to increase contact force across the tibiofemoral joints more than the patellofemoral joint, which appears to be less of an injury concern.
Tibiofemoral compressive forces are critical to knee stability because they provide resistance to anteroposterior translational movement of shear forces. Peak tibiofemoral compressive forces have been shown to occur at roughly 130 degrees of knee flexion. Although internal muscle forces were estimated to be approximately three times the resultant tibiofemoral compressive forces, factors such as fatigue may decrease the stability of the tibiofemoral joint during deep knee squats. Thus, deep squatting with heavy loads that induce rapid muscular fatigue may place the tibiofemoral joint at a higher risk of injury.
Despite the anecdotal reports of increased susceptibility to knee injury with deep squatting, there does not appear to be any conclusive data that indicates an association between controlled deep squatting and injury. Although there is evidence that correlates osteoarthritis and repetitive deep squatting and kneeling in eastern cultures, the religious postures assumed during prayer appear to not adhere to the same technique as a controlled functional squat. Moreover, in healthy clients with no existing knee pathology, there does not appear to be any evidence that deep squatting has any association to knee injury. Therefore, any conclusion that deep squatting leads to knee injury can be regarded as merely speculation.
Lastly, it may be important to consider the degree of deep squatting that will be required during athletic competition or functional activity. Although it may appear to be safe to promote deep squatting during training, it may not be contributing to increased performance or functionality though specificity, thus potentially increasing the risk of injury without contributing to performance. Clearly, there are numerous factors that the strength and conditioning professional must consider when determining optimal squat depth for a particular individual.
David Larson graduated magna cum laude with a Bachelors of Science degree in Kinesiology from Arizona State University and is a Certified Strength and Conditioning Specialist through the National Strength and Conditioning Association. David is also currently pursuing a Masters of Science in Human Movement, specializing in both Sports Conditioning and Geriatric Exercise Science. David has played soccer since he was five and continues to play the game competitively today. David loves when his clients tell him how much their lives have been and are improving through fitness.
Caterisano, A., Moss, R., Pellinger, T., Woodruff, K., Lewis, V., Booth, W., & Khadra, T. (2002). The effect of back squat depth on the emg activity of 4 superficial hip and thigh muscles.Journal of Strength and Conditioning Research,16(3), 428-432, Escamilla, R., Fleisig, G., Zheng, N., Barrentine, S., Wilk, K., & Andrews, J. (1998). Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises.Medicine & Science in Sports & Exercise,30(4), 556-569, Nagura, T., Dyrby, C., Alexander, E., & Andriacchi, T. (2002). Mechanical loads at the knee joint during deep flexion.Journal of Orthopaedic Research,20, 881-886, Schoenfeld, B. (2010). Squatting kinematics and kinetics and their application to exercise performance.Journal of Strength and Conditioning Research, 24(12), p. 3497- 3506, Schoenfeld, B., & Williams, M. (2012). Are deep squats a safe and viable exercise?.Strength and Conditioning Journal,34(2), 34-36.