Forensic Analysis by Dr Paul Batman

Exercise: Squat

Client Instruction

 Starting Position

1. Position your body under a safety rack and slowly lift and rest the bar on your shoulders making sure the bar is off your neck (support maybe needed)
2. Grasp the bar with your palms facing forward about 10-15 cm outside of your shoulders
3. Position your feet slightly wider than shoulder width apart, feet flat on the floor with your toes pointed out at approximately 30 degrees
4. Keep your chin up and eyes focused straight ahead
5. Maintain a flat back position throughout the move with an arch at the base of the spine. The abdominals should be tightened along with the spinal extensors to support the spine in both phases of the exercise

 Down Phase

1. From this starting position, inhale deeply and begin to lower your hips in a controlled manner towards the ground as if sitting in a low chair
2. Aim for a position where the top of your thighs are slightly lower than parallel
3. Avoid any excessive forward lean of the trunk during the descent

Up Phase

1. From this squat position commence with a powerful drive to accelerate out of the bottom position. Straighten your hips, knees and ankles back towards the starting position
2. Shoulders, knees and hips should be aligned over the ankle
3. Keep your heels firmly planted on the floor
4. Upon passing the sticking point (about 30 degrees above parallel) begin to slowly expel air through your mouth

 Muscle Analysis

 Up Phase

Joint                                    Action                         Contraction                                    Muscle Group

Hip joint                                Extension                        Concentric                                    Hip Joint Extensors

Knee Joint                            Extension                        Concentric                                    Knee Joint Extensors

Ankle Joint                        Plantar Flexion                Concentric                               Ankle Joint Plantar Flexors

Down Phase

In the down phase of the exercise the weight is lowered slowly with gravity. The same muscles that concentrically contracted to lift the weight are those that are eccentrically contracting to lower the weight.

General Kinesiological Analysis

In the up phase of a squat the hip joint is extended by the concentric contraction of the gluteus maximus, semimembranosus, semitendinosus and the biceps femoris. The knee joint is extended by the concentric contraction of the rectus femoris, vastus medialis, vastus intermedius and the vastus lateralis. The ankle joint is plantar flexed by the concentric contraction of the gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, flexor digitorum, peroneus longus and the peroneus brevis.

While not included in this analysis the adductors muscles located on the medial thigh can contribute to the hip joint extension in the squat.

Advanced Kinesiological Analysis

The prime movers causing extension of the hip joint are the gluteus maximus, semimembranosus, semitendinosus and the biceps femoris. The prime movers in knee joint extension are the rectus femoris, vastus medialis, vastus intermedius and the vastus lateralis. The prime movers in ankle joint plantar flexion are gastrocnemius and the soleus. The assistant movers are the tibialis posterior, flexor digitorum, flexor hallucis longus, peroneus longus and the peroneus brevis.

In the up phase of the squat, the hip joint muscles neutralize any unwanted medial and lateral rotation that can occur from the contraction of the hamstring muscle group and the gluteus maximus. The vastus medialis and the vastus lateralis are located on either side of the patella, and as such during extension of the knee joint engage in counter current pulling action on the patella. Problems associated with pre-patella pain are often the result of a muscle imbalance between the vastus medialis and the vastus lateralis as they pull on the patella. The ankle joint is plantar flexed by the contraction of the gastrocnemius and the soleus. These muscles insert into the calcaneous via the Achilles tendon. Their line of pull generally does not force them to cause any secondary actions. However, when the tibialis posterior, flexor digitorum and the flexor hallucis longus contract in plantar flexion they can also cause inversion of the ankle. Alternatively, when the peroneus longus and the peroneus brevis assist in plantar flexion they also can cause eversion of the ankle. When all these muscles contract together to cause plantar flexion, they neutralize this additional unwanted inversion and eversion movements at the ankle joint.

The gluteus maximus, semimembranosus, semitendinosus and the biceps femoris all have origins on the pelvis. The pelvic girdle consists of the two pelvic bones and the sacrum (base of the spine). The pelvic girdle can move forward and back, sideways and rotate. When these large muscles of the hip contract to cause a movement of the femur, the pelvic girdle must be stabilized to prevent movement that would prevent these muscles from having an anchor. The abdominals and the spinal extension muscles (located posterior spine) pull in a counter balance manner to ensure that the trunk is held in a fixed position and fully stabilized.

In squat exercises there is an apparent paradox when examining the contraction of the quadriceps and the hamstrings. In the up phase of a squat, the quadriceps contract to cause extension of the knee joint while the hamstrings are contracting to cause extension of the hip joint. It may be surprising to find that all these muscles are active, as they are responsible for causing different actions. It would seem plausible that both these muscle groups should neutralize the others movements, with no resultant movement. This contradiction has been defined as “Lombards Paradox”.

Lombards paradox states that in hip joint extension, the lever arms of the hamstrings in hip joint extension is greater than the lever arms for rectus femoris (quadriceps) in hip joint flexion. Assuming that the force generated within these two muscles is equal, the torque of the hamstrings for hip joint extension is greater than the torque of the rectus femoris in hip joint flexion. Similarly, the lever arm of the rectus femoris in knee joint flexion is greater than the lever arm of the hamstrings for knee joint flexion. The torque produced by the rectus femoris in knee joint extension overrides the torque produced by the hamstrings in knee joint flexion. The lever arm differences at the hip and knee joints, allows the muscles to perform their movements through the full range of motion.

The most powerful muscle that causes hip joint extension is the gluteus maximus. This is the largest fleshy muscle in the body. The gluteus maximus demonstrates the body’s link system. From a standing position with the feet parallel, when the gluteus maximus contracts there is an obvious lateral rotation of the hip joint. Further lateral rotation of the hip joint is prevented by the feet being in contact with the ground. In this position the force of the lateral rotation of the hip joint is transmitted to the tarsal bones, resulting in inversion of the ankle joint and a decrease in the arching of the spine. The gluteus maximus is generally recruited in large hip joint extension movements. Studies have reported that the hip joint must be flexed in excess of 45 degrees from the trunk unless there is a strong resistance. This can be seen when cyclists lean forward over the handle bars to decrease the angle between the hip joint and the trunk to activate the gluteus maximus to a greater extent. When climbing stairs, old people lean forward for exactly the same reason.

There a numerous variations to the squat.

Back squat (narrow and wide stance)

In the back squat with a narrow and wide stance, the three vasti muscles are stressed significantly. The rectus femoris, semimembranosus, semitendinosus and the biceps femoris are recruited only moderately.

Front squat (free standing and with smith machine)

In the front squat variations the three vasti muscles are again recruited significantly, with the hamstrings used only moderately.

Hack squat machine (different feet positions)

The hack squat completed on a machine recruits the vastus lateralis, vastus intermedius, adductor magnus and adductor brevis significantly. The hamstrings are recruited moderately as well as the vastus medialis and the rectus femoris.

Hack squat (free weight barbell)

The hack squat requires the barbell to be secured behind the buttock of the client. A normal squat follows this starting position. In this exercise, the four quadriceps muscles are recruited maximally. The hamstrings and adductors are used minimally.

In studies that have reported the muscle recruitment pattern for the squat variations, all were performed with the client only descending to 90 degrees of knee flexion. This indicates that for more hamstring and gluteus maximus involvement, it might be preferable to go deeper in the squat beyond 90 degrees. This must be approached with caution, as the deeper a client goes the greater potential for injury. It is important that if deep squats are prescribed they are completed after a series of progressive exercises that strengthen all associated structures around the knee joint to enable it to cope with the additional stress.