Barbell back squats are an exercise staple to lifters, both recreational and competitive. This exercise has been studied to offer many benefits to strength, hypertrophy and performance (Schoenfeld & Williams, 2012). Yet, there are existing debates amongst gym-goers and exercise professionals as to whether or not deep squats (beyond parallel) are safe and viable. This article will explore whether or not deep squats are safe for the tibiofemoral (knee) joint and their usefulness to lifters and athletes.
In 1961 a study was produced by Klein which argued that deep squatting led to laxity (looseness) of the anterior cruciate ligament (ACL). The device he used was self-made and he reported that competitive weightlifters who frequently deep squatted displayed higher laxity than a control group (Klein, 1961). He later produced another study where he concluded that squats should be performed no deeper than parallel without drastically increasing the risk of compromising the stability of the knee (Klein, 1962). This led to many institutions such as the American Medical Association following suite and adopting the position that deep squatting should be avoided in order to decrease risk of injury (Schoenfeld & Williams, 2012). Even the United States Army and New York School system made changes to their protocols in order to avoid any activity that included deep squatting. This study is believed to be a root for many of todays concerns for the safety of deep squatting.
Ten years later Meyers (1971) replicated the study of Klein and even used a copy of the same instrument that Klein used and found no significant differences in knee stability between the deep squatters and the half squatting subjects. Chandler, Wilson and Stone (1981) studied a group of male powerlifters and competitive weightlifters who frequently performed deep squats and compared their knee stability to a control group. It was found that the powerlifters and weightlifters had significantly better knee stability and joint capsule tightness.
Concerns for the safety of the ACL seem to diminish given that studies have shown that the forces on the ACL during a squat peak between 15-30 degrees of knee flexion and drastically decrease after 60 degrees of flexion (Schoenfeld & Williams, 2012). Another ligament of concern is the posterior cruciate ligament (PCL). But, peak forces on the PCL are found to be at 90 degrees of knee flexion and rapidly decrease thereafter (Schoenfeld & Williams, 2012). It would seem that deeper squats actually decrease the risk for ACL and PCL injury. But, as squat depth increases, so do compressive forces on the menisci and the articulating cartilage, peaking around 130 degrees of knee flexion (Schoenfeld & Williams, 2012). This would lead to more concern for these areas of the knee, rather than the ACL or PCL. Escamilla (2001) argued that the pressure between the underside of the patella and the femur during a deep squat could increase the risk for patellofemoral degeneration. Additionally the anterior shear forces were significantly lower between 0-60 degrees of knee flexion. Despite these studies that show how much pressure is being put on various parts of the knee during a squat, no cause-effect relationship has been exhibited in the research for healthy individuals with no prior pathology. Schoenfeld (2012) suggests that there may be reason for concern for individuals with a history of osteoarthritis, chondromalacia, osteochondritis and/or persons who have had prior repairs to the menisci or PCL. Beyond this, any concerns for safety are only speculative.
Even though the risks for deep squatting are speculative, why risk it? What are the benefits of a deep squat compared to a squat that is above parallel? Different degrees of knee flexion during the squat will produce different muscle activation. Therefore it becomes a matter of matching the squat depth to the goal of the athlete and specificity of their sport. Gluteus maximus (GM) activation has been studied to change very little between a partial squat and a parallel squat, but shows significant increases to activity during the full squat (Schoenfeld, 2010). Therefore if the goal of the athlete is to squat for GM activation, then a full squat would be the best recommendation.
However, hamstring activation maximizes between 10-70 degrees of knee flexion (Schoenfeld, 2010). Therefore athletes seeking hamstring outcomes would see no additional benefit to squatting below parallel. Quadriceps are similar, showing no increase in activation after 90 degrees (parallel) (Schoenfeld, 2010). Athletes seeking to simply develop their quadriceps wouldn’t need to perform a deep squat.
A final consideration would be specificity to the sport. It is within the rules of competitive powerlifting that the athlete break parallel during their squat in order to be considered a good lift. This would obviously suggest that powerlifters should at, or below parallel. But what about other athletes, like a basketball player? Williams (2012) argues that during very few sports are the athlete actually performing deep squat motions. Given that the majority of basketball jumps happen above 90 degrees of knee flexion, it may be more sport-specific to stop at parallel. But, many athletes do more than just jump. A basketball player also sprints and changes direction quickly. The GM is active during all of these motions and contributes to performance.
So why not just deep squat and get the benefit to all of the muscle groups instead of just some? One reason may be that heavier loads could likely be used during higher squats, therefore increasing mechanical tension on the more useful muscles. Working under greater intensities (loads) increases outcomes of performance and hypertrophy, depending on the design (Schoenfeld, 2010).
Given the current research it appears that most concerns for safety during deep squats are speculative at best. Besides persons who have prior injuries/pathology, there seems to be no reason for concern that deep squatting will injure or compromise the knees in any way. My suggestion would be that athletes who are seeking the most muscle activation for hypertrophy or weight loss, without prior pathology, perform full squats. Also those who’s sports require a deep squat. A jumping athlete would likely see more performance outcomes from a parallel squat, given that they likely can work under heavier loads. But, this isn’t to say that even jumping athletes couldn’t see a benefit from periodizing their programming to include both deep and partial squats.
References
Chandler, T., Wilson, G., & Stone, M. (1989). The effect of the squat exercise on knee stability. Medicine and Science in Sports and Exercise, 21, 299-303.
Escamilla, R. F. (2001). Knee biomechanics of the dynamic squat exercise. Medicine and Science in Sports and Exercise, 33, 127-141.
Klein, K. (1961). The deep squat exercise as utilized in weight training for athletes and its effects on the ligaments of the knee. Journal of the Association for Physical and Mental Rehabilitation, 15, 6-11.
Klein, K. (1962). The knee and the ligaments. Journal of Bone and Joint Surgery, 44, 1191-1193.
Myers, E. J. (1971). Effect of selected exercise variables on ligament stability and flexibility of the knee. Research Quarterly, 42(4), 411-422.
Schoenfeld, B. J. (2010). Squatting kinematics and kinetics and their application to exercise performance. Journal of Strength & Conditioning Research, 24(12), 3497-3506.
Schoenfeld, B., & Williams, M. (2012). Are deep squats a safe and viable exercise? Strength & Conditioning Journal, 34(2), 34-36.