What is the ideal safe range of movement during the squat exercise when you care about your knees? A look at the different ranges of motion.
What Is A Squat?
Basically every time you sit down on a chair, you perform a squat: bending the knees until you sit down. As the picture below shows, the difference between sitting down in a chair and doing the same motion as an exercise is that during the exercise there normally is no chair and you will use additional weight in the form of dumbells or a barbell to make the movement more difficult.
What makes the squat a great exercise is that it activates all muscles in the leg, from the quadriceps, hamstrings, glutes to the calf muscles, as well as those in the lower back, which stabilize the upper body during the movement. And when when performed correctly, it won’t cause problems to your spine.
Forces On The Knee
But what about the knee? Studies in the 1950s and 1960s came to the conclusion that the squat itself, even when done correctly, causes harm to the knees, but these studies later were discredited, as they involved parachute jumpers, who, due to the nature of their trade itself, are prone to unstable knees.
However, a 1993 study took experienced lifters and examined the load on the hip and knee at four different knee flexion angles: 45°, 90°, parallel and deep squats.
The researchers found no differences in the load between the 45°, 90° and parallel angles, but the deep squat showed significantly more stress for the knee.
A second study looked at the compressive force between the quadriceps tendon and the femoral intercondylar fossa (the knee notch of the thigh bone), where higher forces can mean injury to the tendon.
The force began with 6000 N at 130° knee flexion, decreased to about 1750 N at 90° and was at approximately 0 N at 60° (Nisell R, Ekholm J. Joint load during the parallel squat in powerlifting and force analysis of in vivo bilateral quadriceps tendon rupture. Scand J. Sports Sci. 8(2):63–70, 1986, found in Garret, William, and Donald Kirkendall. Exercise and Sport Science. Philadelphia: Lippincott, Williams & Wilkins, 2000. 589).
A review (PDF) from Duke University of the available literature summarizes this as follows:
For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.
Quadriceps Or Gluteus Maximus?
The other interesting question we have to examine is what muscle actually benefits the most from these different ranges of motion.
A study from 2002 (PDF) showed that up to parallel position, the most involved muscle in the squat is the quadriceps. After parallel, the muscle becoming most active is the gluteus maximus, which means by going below parallel, you shift activity from your quadriceps to your behind.
That the hamstrings are more active during a deep squat is therefore something you often read on many bodybuilding and fitness sites, but nothing supported by science – maximum hamstrings activity tends to occur at 10 – 70 degrees of flexion.
Going below parallel (deep squat) causes the greatest risk to the knee without increased benefits to your quadriceps development. If at all, this “full squat” is only worthwhile for those that explicitly want to train their gluteus maximus and have healthy knees to begin with. The ideal trade-off between maximum effect of the exercise and least risk is the parallel squat.
Picture courtesy of Amber Karnes.