Biomechanics of the Squat
My article Squatting kinematics and kinetics and their application to Exercise Performance has just been published in the current issue of the Journal of Strength and Conditioning Research. The article is an in-depth review of the literature on squat biomechanics and examines its relevance to strength and muscle development. Here are the paper's conclusions, based on a summary of the research: cabergoline-steroids
1. The squat depth should match the person's goals and abilities. Because the highest patellofemoral compression forces occur at or near maximum knee flexion, individuals with patellofemoral disorders should avoid squatting at high flexion angles. In individuals with an existing injury or previous reconstruction of the posterior cruciate ligament, it is best to limit flexion to 50° to 60° to minimize posterior shear. Quadriceps development is maximized by squatting in parallel with no additional activity seen at higher flexion angles. Hip extensor moments increase with squat depth, so full squats can be beneficial for those looking to maximize hip muscle strength.
2. The speed of movement should be guided by the target specificity of the force-velocity curve. However, since speed of movement has been shown to significantly increase both compression and shear forces, there is a trade-off between optimal power transfer and risk of injury. This is especially true in the eccentric aspect of the movement, where rapid deceleration creates excessive joint forces at the knee. If the descent is not controlled, ballistic contact can occur between the hamstrings and calf muscles, which can have a dislocating effect on the knee ligaments. Therefore, the descent into the squat should always be performed in a controlled manner unless athletic goals specifically dictate otherwise, with an eccentric tempo of 2 to 3 seconds being considered a general guideline.
3. A wider squat is preferable for those targeting optimal hip adductor and hip extensor development, while a narrower stance is better for targeting gastrocnemius development. The stance can also be varied to alter joint-related forces: a narrow stance helps minimize patellofemoral and tibiofemoral compression, while a wider stance results in less forward knee movement, thus reducing shear forces.
4. Low bar squats tend to generate more hip extensor torque and less squat torque compared to high bar squats. However, the magnitude of the forces for both movements are well tolerated by the associated joint structures, making either position suitable for the majority of trainees. The front squat creates significantly less knee compression and lumbar strain compared to back squats, making it a viable alternative for people suffering from various knee and back conditions. Front squats can also be particularly beneficial for those who compete in weightlifting, as they are an integral part of performing the clean.
5. Fatigue can have a deleterious effect on squatting technique, potentially leading to knee instability and increased lumbar shear. If the lifter opts to squat to momentary muscular failure, it is advisable to have a spotter to ensure safety.
In addition to the aforementioned joint-specific recommendations, some joint-specific recommendations can be made as to squat-related performance variables.
Ankle Joint: Significant strength and mobility is required at the ankle for proper squat performance. Feet should be positioned in a comfortable stance that allows the knees to move in line with the toes. Because the feet are outwardly rotated approximately 7° in anatomic position, this can be considered a good starting point to ensure proper patellar tracking. If the lifter’s heels rise off the floor during the eccentric phase of movement, efforts should be made to improve flexibility around the talocrural and subtalar joints. Orthotics can be worn to help correct joint imbalances and misalignment. If necessary, a barbell plate or other flat object can be placed underneath the heels to aid in stability.
Knee Joint: Given the fact that shear forces are increased as the knees move past the toes during the downward phase of the squat, attempts should be made to avoid significant forward knee translation on descent. However, this should not be done at the expense of compromising form at the hips and spine, which can place the lumbar region in a biomechanically disadvantageous position and significantly increase spinal shear. To reduce tibiofemoral and patellofemoral moments, the lifter should sit back into the squat during descent and resist pushing the knees forward. There should be no varus or valgus motion throughout exercise performance.
Hip Joint: Given the close relationship between movement at the hips, pelvis, and lumbar spine during dynamic squatting, hip mobility is extremely important for proper squat performance, especially at higher flexion angles. Poor joint mobility can lead to greater forward lean and thus increased spinal shear. Although some lifters attempt to increase hip flexion by using posterior pelvic movement during squat descent, this can heighten lumbar stress and is thus not advisable. Flexibility training specific to the hip musculature can help to increase hip mobility and facilitate better squat performance.
Spine: The spine is the most vulnerable of the joints during squatting. Because the lumbar spine is better able to handle compressive force than shear, a normal lordotic curve should be maintained in this region, with the spinal column held rigid throughout the movement. Proper spinal alignment is facilitated by maintaining a straight ahead or upward gaze, which reduces the tendency for unwanted flexion. Although some forward lean is sometimes necessary to maintain stability especially when performing deep squats, attempts should be made to keep the trunk as upright as possible to minimize shear. No lateral movement should take place at any time.
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