A look into the biomechanics of squat depth
Squats: 90 degrees or 'ass to grass'?
Squats are one of the great exercises. However there exists much conjecture as to how they should be performed. Concern surrounding deep squats, beyond 90 degrees of knee flexion, originated from a study conducted by Karl Klein at the University of Texas. Klein compared weightlifters that frequently performed deep squats with a control group, and it was discovered that there was an increased incidence of laxity in all knee ligamentous structures in the test group. Moreover, it was deemed that squatting below parallel (90 degrees of knee flexion) had a detrimental effect on ligamentous stability. This resulted in a position statement being released by the American Medical Association (AMA) cautioning against the use of deep knee exercises.
In light of Klein's significant findings, more research into the issue has been conducted revealing completely different results. Most studies have determined there is no correlation between deep knee squatting and injury risk. Chandler et al. provided positive evidence for the use of deep knee squats, after comparing a group of male powerlifters to a control group. It was discovered that the male powerlifters who all frequently employed a deep squatting technique, had significantly tighter joint capsules on anterior drawer tests and were also tighter on the quadriceps active drawer test at 90 degrees of flexion.
Forces acting through the main passive knee restraints of concern, the ACL and PCL; have been shown to diminish at higher degrees of flexion. Peak ACL forces occur between 15 and 30 degrees of flexion, leveling off thereafter at higher flexion angles. PCL forces rise consistently from 30 until 90 degrees where they peak, and then decline significantly as flexion continues to increase. In terms of muscle function, average muscle activity of the gluteus maximus has been found to be significantly different when comparing partial and parallel to deep full squat depths (Caterisano et al). Similar results were found with regards to peak values, where there was significantly greater muscle activity during full squats. In contrast to the findings surrounding gluteus maximus muscle recruitment, squat depth has little effect on hamstring involvement as the magnitude of variation in peak and mean torques does not vary greatly. Due to the bi-articular nature of the muscles, as they work across the knee and hip joints flexing and extending each respectively, muscle lengths and forces remain fairly constant throughout performance. Most of the muscular forces occurring at the knee are produced by the quadriceps, namely quadriceps femoris. Peak muscle activity from this structure is found to occur at 80 to 90 degrees of flexion and remaining relatively constant from then on.
So get you arse to the grass!
In conclusion, there is little evidence to suggest that deep squats compromise knee structure and function. This is further supported by findings associated with the behaviour of the passive and active restraints acting upon the knee during differing degrees of knee flexion. The depth of squat prescribed by personal trainers should be based upon the performance-orientated goals of the client, and considered along with any pathological issues that may present. For optimal quadriceps involvement a depth of 90 degrees of knee flexion is suffice, while development of gluteus maximus should involve greater angles of knee flexion.
Fit Education says "Get your ass to the Grass!"
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