Although the squat is one of the most common exercises used in resistance training programs it is often not performed properly. The squat is a great exercise in that it works multiple joints and muscles. It is also functional as it mimics movements involved in activities of daily living as well as sports skills. Scientists estimate that over 200 muscles are active during a squat with the dynamic movement targeting primarily the Quadriceps, Gluteus Maximus, inner and outer thigh muscles, and the Gastrocnemius. The Hamstrings contract moderately during the squat but produce twice as much activity during a leg curl or stiff legged deadlift. In addition, torso muscles contract statically to maintain posture during the exercise.

The squat exercise can be modified to fit into exercise programs for a variety of persons with varying needs, health conditions, and goals by changing the depth. For example, you can perform quarter squats (40 degrees of bend at the knee), half squats (70 – 100 degrees of knee bend) or deep squats (greater than 100 degrees of bend at the knee). In addition, you can vary the load, foot position, speed of movement, surface, and position of the load. There are lots of myths about the squat exercise but let’s do some fact finding. A recent article in Journal of Strength and Conditioning Research¹ reviewed the scientific literature regarding both benefits and risks of the squat exercise.

How deep should you squat? Research shows that if you squat to a level where the thighs are parallel to the floor, quadriceps activity is maximal and does not increase as the squat becomes deeper. Deeper squats, however, do increase muscle activity in the Gluteus Maximus. The down side of deep squats is that compressional forces are greater on the knee. Compressional forces are vertical forces that tend to squeeze the structures above and below the knee joint together, increasing pressure on the cartilage and menisci. For most individuals with a goal of lifetime fitness, half squats provide the most benefit with the least risk. For healthy athletes, the benefits of performing some full squats may be worth the extra risk.

How does increasing resistance affect the squat? The greater the load, the greater the compressional forces in the knee and spine. So persons learning proper form or with knee or back problems should be cautious about adding too much resistance. As the load increases, the amount of forward bend (flexion) at the hips increases. This raises compressional forces in the spine and increases hyperextension (arching) of the spine. For this reason, maintenance of a normal spinal curve should be emphasized, avoiding an arched or flattened back position.

Wide vs. narrow stance, does it matter? A wide stance targets the inner (Adductor Group) thigh and Gluteus Maximus compared to a narrow stance which targets the Gastrocnemius. The narrow stance (107% of shoulder width) position decreases knee compression forces but produces higher shear forces on the knee than a medium (142% of shoulder width) to wide (169% of shoulder width) stance. Shear stress occurs when two structures are moving in the opposite direction like dragging one book across the top of another. Too much shear stress can lead to ligament injuries.

Does movement speed make a difference? Yes, both knee compressional and shear stress increase as movement speed increases. If you bounce at the bottom of a squat, shear forces increase an additional 33%. The recommended tempo for the lowering phase of the squat is 2-3 seconds to reduce stress on knee ligaments. The spine is also affected with compression forces doubling at high lifting speeds. Certainly, faster movement speeds better mimic sports activities but always weigh the increased risk against the benefits.

Does placing the load in the front vs. back make a difference? Researchers studying which muscles are overloaded most reported that although the Gluteus Maximus showed more activity during the back squat and Quadriceps during the front squat, this difference was not significant. However, knee compression forces were lower during the front compared to the back squat. For this reason, a front squat may be less stressful for persons with knee ligament or meniscal problems.

Is it safe to squat to fatigue? The concern with squatting to fatigue is that often form is compromised, which can lead to injury. As the muscles fatigue, the ability of receptors in the muscles and joints that sense body position is reduced. Muscle fatigue and poor receptor function can negatively affect form and result in a more unstable knee and spine. One study reported that lifters lost their upright positions and began flexing the low back when muscles started to fatigue during the squat. This change in form increases the stress on the low back, which increases the risk of injury. Careful attention to lifting form, especially the spine is critical. Stop the lift if form is compromised. Remember that the spine is the joint most susceptible to injury when performing a squat.

So what does good form look like?

• Avoid exaggerated foot placements, using a comfortable stance where knees can move in alignment with the toes. Heels should stay on the floor as the body is lowered. If not, exercises to improve ankle flexibility should be added to the program.
• Sit back when performing a squat so that the knees don’t move out over the toes. If you can’t see your toes, you need to sit back more. Check knee position as knees should not roll in or out during the exercise.
• Avoid too much hip flexion as it can increase shear stress on the low back. Poor mobility may result in greater forward lean during the squat. To reduce excessive forward lean, incorporate flexibility exercises for the hip and pelvis into the exercise program.
• To protect and stabilize the spine, maintain a normal low back curve during the lift while minimizing forward lean throughout the movement. Forward lean increases shear stress on the disc and other structures. Keeping the eyes and head forward and level will assist in keeping the normal spinal curve and minimize forward lean. A flat back position should also be avoided.
  

The squat can be both time efficient and functional.  The best body positioning for a squat depends on an individual's goals, history of injury and lifting experience. Do you notice that body position can affect the muscles that fatigue, range of motion and joint comfort during a squat?  Have you modified your form to increase the effectiveness of the exercise or reduce the risk of injury?  

¹ Schoenfeld, B.J. (2010). Squatting Kinematics and Kinetics and Their Application to Exercise Performance. Journal of Strength and Conditioning Research. 24(12), 3497-3506.