In my previous blog post, Should I Be Doing Squats, I explained the benefits of training the fundamental movement pattern of squatting. When engaging in an exercise program, the way you move is vital for overall health and performance. Within the realm of your exercise techniques are the cues and instructions given by coaches, fitness trainers, physical therapists and physicians. You also have the interim reality of internet opinions weighing in.
Keeping the knees behind the imaginary vertical line of the toes is a cue frequently given when instructing someone to squat. This “over-cue” may be the result of certain biomechanical studies — showing compression forces on the patella-femoral joint with a knees forward approach — that have since been extrapolated to all populations. What may be at issue here is the suggestion of a one-size-fits-all approach to teaching the squat.
INITIATING THE SQUAT
Squatting is a coordinated movement between the trunk, hips, knees, and ankle joint staying balanced over a stable foot on the ground. The excess stress may occur when the knees become the primary mover and end up moving forward while initiating the squat. This results in a loss of contribution from the other joints and their associated musculature to distribute pressure from the knees. Simply cueing the hips to move slightly before (or simultaneously with) the knee bending motion can limit the early and excessive forces applied to the knees. This easy adjustment allows your hips to sit back while keeping the tibia relatively vertical initially.
As the squat progresses to 90 degrees and into a deep squat, the knees will translate in front of the plane of the toes requiring more dorsiflexion motion at the ankles. This has mostly to do with staying balanced without folding over. In other words, the anterior translation of the knees occurs to achieve balance while maintaining a relatively upright torso, especially when applying external loads. There are exceptions to this rule based on body length proportions, such as having a shorter torso with longer femurs; however, we will not dive into that tangent at this time.
Maintaining balance with body-weight squat patterns is one thing for anterior knee translation, but how does this apply when you are squatting with an external load? So once again this concept has to do with balance and where the center of mass or gravity is located on an individual. For a strong and effective squat, you should keep your center of mass in a vertical line over the middle part of your stable foot on the ground. Here are some popular examples of loaded squats:
1. Front Loaded Squat
A front loaded squat (ex: barbell front squat or goblet squat) has a center of mass that is higher and more forward on the body compared to a bodyweight squat. This squatting variation requires a more upright trunk posture in order to keep the weight supported on the shelf created by your shoulders and arms. This position does not allow the hips to sit back as much and results in more anterior knee translation. Try performing a front squat or goblet squat with your hips far back and you will immediately notice how much harder it will be to hold that weight, especially as it becomes heavy.
2. Low bar back squat
On the other end of the spectrum, a low bar back squat, which is typically seen among powerlifters, shifts the center of gravity more posterior. The barbell typically sits on a muscular shelf created around the mid portion of the scapula/shoulder blades and posterior deltoid muscles. This requires a more bent forward spine position, sitting the hips further back, and results in minimal knee anterior translation. Also, the forward bent spine decreases the vertical pull of gravity for the barbell sliding off of the back, if the spine were more upright.
3. High bar back squat
The most common variation of barbell squatting seen amongst competitive lifters, recreational gym goers, and with athletes in training is the high bar back squat. With this variation the bar sits on a shelf created by the upper trapezius muscles of an individual. This position creates a happy medium between the two previously described types of squats. Pending body limb measurements, mobility, or technique, the high bar back squat can either have knees that do or do not pass the toes when approaching a parallel thigh position.
BALANCING THE STRESS
Yes, allowing knee anterior translation has been shown to place more stress on the knee joint compared to restricting the knees from moving past the toes. However, these torques or stresses do not simply disappear. While limiting forward knee movement decreases torque forces placed on the knee, it significantly increases the torque forces that are placed on the hips and the spine. This has to do with the more bent forward spine and hip position in order to maintain balance. So the forces that you are redirecting from your knee have to end up somewhere else.
Stress is not necessarily a bad thing. Appropriate stresses to the body can result in the body adapting and becoming stronger and more resilient. The key to managing all of the increased stress placed on the body is to create a balanced distribution to where these stresses are placed and how much/often you are placing stress in the area. Biomechanical studies on squatting suggest that it may actually be advantageous to permit the knees to move slightly beyond the toes when in a parallel squat position for optimal load management between all involved joints.
Furthermore, increasing the amount of options you have for squatting can allow not only variability of technique for performance, but also allow different options to not overly stress one particular pattern. This can also be heavily influenced by the style or goal of training. While the back squat techniques can typically produce more force and can decrease the amount of forward knee translation, the front squat is essential for those who perform the Olympic lifts or participate in Crossfit.
These variable squatting techniques can also be very useful in managing nagging injuries or painful patterns while training. Because of the more upright trunk position and decreased shear stress on the spine, the front squat or goblet squat may be a better option for those who may be having some low back or hip issues.
For those who are recovering from some knee pain or injury, training low bar back squats or box squats may be great options to achieve a training stimulus without stressing the knee too much. As always, it would be best to consult with a qualified physical therapist or other healthcare practitioner who understands your sport if you are dealing with injuries while training.
Disclaimer: The views expressed in this article are based on the opinion of the author, unless otherwise noted, and should not be taken as personal medical advice. The information provided is intended to help readers make their own informed health and wellness decisions.
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- Fry AC, Smith JC & Schilling BK. Effect of knee position on hip and knee torques during the barbell squat. JSCR. 2003. 17(4):629-633.
- Hartmann, Hagen & Wirth, Klaus & Klusemann, Markus. (2013). Analysis of the Load on the Knee Joint and Vertebral Column with Changes in Squatting Depth and Weight Load. Sports medicine (Auckland, N.Z.). 43. 10.1007/s40279-013-0073-6.