the science of squatting
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ciencia do agachamentoTRANSCRIPT
Everything You Always Wanted to Know About the Squat…But Were Afraid to Ask
Brad Schoenfeld, MSc, CSCS, CSPS, NSCA‐CPT
Why Squat?
• “King of all exercises!”– Highly functional
• ADLs• Athletics
– Over 200 muscles activated• Metabolic benefits• Hypertrophy
Hip Joint: Functional Anatomy
• Ball‐and‐socket joint • Freely mobile in all three planes of movement– Flexion and extension in the sagittal plane,
– Abduction and adduction in the frontal plane
– Internal/external rotation in the transverse plane
Hip Torque During Squatting
• Hip extension torques increase in conjunction with increases in hip flexion to approximately a parallel position• Forward lean is positively
correlated to increased forces about the hip joint
Hip Musculature During Squatting
• Activity of the gluteus maximus exhibits a positive relationship with squat depth
• Hamstrings only moderately active during the squat and relatively unaffected by squat depth
Knee Joint: Functional Anatomy• Tibiofemoral joint
– Modified hinge joint– Small amount of axial rotation present during dynamic movement
• Patellofemoral joint– Gliding joint
• Provides additional mechanical leverage in extension
• Reduces wear on the quadriceps and patellar tendons from friction
Forces Acting at the Knee
• Compression– Force applied longitudinally (“squeezing force”)
– More easily handled than other forces
Compressive Forces at the Knee
• Both tibiofemoral and patellofemoralcompression has been shown to increase with increasing knee angle.
• These forces thought to provide a protective function at knee by initiating a co‐contraction between quads and hams and thus protecting against excessive shear.
• Menisci and articular cartilage under greatest stress at high compression
Forces Acting at the Knee
• Shear– Force applied perpendicular to long axis
– Not well handled by soft tissue structures
– Cruciate ligaments most affected by shear
• Two main shear forces during squat:– Anterior shear– Posterior shear
Anterior Shear Forces at the Knee
• Maximum anterior shear forces during the squat tend to occur within the first 60 degrees of knee flexion – The ACL provides approximately 86% of the restraining force against anterior shear
Posterior Shear Forces at the Knee
• Posterior shear begins to manifest at about 30 degrees of flexion, reaching approximately 90 degrees.– The PCL exerts the primary restraint against posterior shear
Knee Musculature During Squatting
• Quadriceps activity tends to peak at approximately 80 to 90 degrees of flexion, remaining relatively constant thereafter. – Suggests squatting past 90
degrees might not result in further enhancements in quadriceps development.
• Vasti muscles about 50% more active than the rectus femoris
Ankle Joint: Functional Anatomy• The ankle complex is comprised of the talocrural and talocalcaneal joints.
• During squat performance, the talocrural joint facilitates movement through the actions of dorsiflexion and plantar flexion while the primary action at the subtalar joint is to maintain postural stability and limit eversion/inversion at the foot.
Ankle Musculature During Squatting
• The gastrocnemius shows only moderate levels of activation during squatting
• Soleus is more active than the gastrocnemius when squatting at high degrees of flexion.
• Plantarflexors more sensitive to squat load than to depth
Spine: Functional Anatomy
• Gliding joint—multiple joints that interact with one another
• 24 vertebrae—7 cervical, 12 thoracic, 5 lumbar
• Bottom portion consists of sacrum (5 fused vertebrae) and coccyx (4 fused vertebrae—tail)
• Starts small on top and gets progressively bigger on bottom– Support more weight– Provide larger base for muscle
attachment
Disc Function The intervertebral discs form cartilaginous joints between adjacent vertebrae Stabilize the spine by anchoring the vertebrae to one another Facilitate multi‐planar spinal movement and help absorb vertebral shock
Disc Anatomy Discs are comprised of three distinct portions: an outer layer annular fibrosus, a central nucleus pulposus, and two hyaline cartilage endplates . The annulus serves to resist outward pressure during axial compression, stabilize the vertebral joint during motion and contain the inner nucleus
The nucleus functions as a "water pillow," helping to cushion the vertebrae from axial loads and distribute pressures uniformly over adjacent vertebral endplates.
The endplates serve to prevent the nucleus from protruding into adjacent vertebrae as well as helping to absorb hydrostatic pressure caused by spinal loading and allowing for nutrient diffusion
Discs Illustrated
Spinal Forces During Squatting• Squatting with flexed lumbar spine decreases the moment
arm for the lumbar erector spinae, reduces tolerance to compressive load, and results in a transfer of the load from muscles to passive tissues, heightening the risk of disc herniation
• Squatting with 2 degree increase in extension from neutral position heightens compressive forces in the posterior annulus by a clinically meaningful average of 16%
• Proper squat technique requires a rigid spine that eliminates any planar motion. – Ensures a stable, upright posture is maintained throughout
movement– Increasing intra‐abdominal pressure may serve to further
alleviate vertebral forces.
Spinal Musculature During Squatting• The lumbar erector spinae(e.g. iliocostalis lumborum, etc) are particularly important during the squat as they help to resist vertebral shear and maintain anteroposteriorspinal integrity, providing the greatest contribution to spinal stabilization
• Weak erectors can limit squat strength
Spinal Musculature During Squatting
• The back squat involves significant static recruitment of the anterior core musculature– Greater rectus abdominis activity than the traditional plank
Safety of Deep Squats
Study by Klein at University of Texas in the early 60’s showed deep squats caused laxity in the collateral and anterior cruciate ligaments, predisposing them to injury.
In 1962, the AMA came out against any deep knee exercises, citing their "potential for severe injury to the internal and supporting structures of the knee joint."
Follow‐Up Studies
• Subsequent studies replicating Klein’s protocol did not find reduced stability in weightlifters
• Forces on ACL and PCL actually reduced at high flexion angles– Knee structures highly constrained at angles greater than 120 degrees
– Shear forces reduced– Much less anterior and posterior tibial translation and tibial rotation
– Better stability and greater tolerance to load.
How Low Should You Go?
• Athletics• Hypertrophy• ADLs
Deep Squats: Contraindications• Greatest risk of injury are to menisci and articularcartilage– Under increased stress at high flexion angles due to greater compression.
• May be increased susceptibility to patellofemoraldegeneration due to stress from contact of underside of the patella with articulating aspect of femur.
• Femoroacetabular impingement reduces ROM at hip• Essential to consider an individual’s pathologic condition in determining optimal squat depth.
Knees Over Toes?• Fry, et al. had 7 recreationally trained
males perform three unrestricted squat lifts and three restricted lifts where a wooden board was placed immediately in front of both feet so that the knees were prevented from moving forward past the toes. – Knee torque increased from ~117 vs
~150 Nm in the unrestricted squat.– Hip torque was increased during
restricted squatting (~303 vs ~28 Nm)– Greater forward lean in restricted
squats result in increase shear forces at the lumbar spine.
Gaze• Downward gaze shown to increase trunk flexion by 4.5 degrees and hip flexion by approximately 8 degrees compared to a straight ahead or upward gaze
• Given that excessive trunk and hip flexion can place excessive torque on the vertebral column, this suggests it is beneficial to maintain either a straight ahead or upward gaze during performance.
Bar Position
• High Bar Squat– Greater knee extensor torque and
less hip extensor torque vs low bar• Low Bar Squat
– Greater hip extensor torque and less knee extensor torque vs high bar
• Front Squat– Lower maximal joint compressive
forces at the knee as well as reduced lumbar stress as compared to back squats
– May target the quadriceps to a greater degree than back squats
Foot Placement• Narrow stance (87 to 118% of shoulder width)
– Greater gastroc activity– Increases forward knee translation by 5 cm (shear)
• Wide stance (158 to 196% of shoulder width) – Greater gluteues maximus, hamstrings and adductor activity
– Increases compression forces by ~15%• Foot position (hip/tibial rotation)
– Greater adductor activation– Knees should track in line with toes
For Further Reading