The primary objective of performance orientated strength and conditioning is the gain of muscle cross-sectional area (hypertrophy strength training) or the
enhancement of inter-and intramuscular coordination (strength/power training) for which high
training intensities are necessary (9). For this purpose, the squat is
one of the most effective exercises in athletic training (11,16,5).
It is a movement that is performed loaded or unloaded by flexing and extending the hip, knee, and ankle joints in a manner similar to many movements that occur in daily activity and sport (5). The squat exercise is regarded as a closed kinetic chain exercise where the force is expressed through the end of the limb while it is fixed to ground (5). Individuals performing the squat use a variety of techniques that are of personal preference and believed to reduce the risk of injury and be more beneficial for the development of specific muscles (6).
Weightlifters have commonly believed that changing joint position can alter specific muscle activation and the line of pull of the muscles, altering their natural length tension relationships (2). The 'length tension relationship' is a biomechanical principle where variation in muscle tension occurs due to changes in muscle length (2). The length of the internal muscle fibres, which are the actin and myosin filaments of the sarcomere, determines the magnitude of force produced by the muscle fibre and ultimately the whole muscle (14).
Squat Variation 1: Wide stance/parallel
From a performance enhancement and injury risk
perspective, it is commonly recommended that movement strategies used to perform
the squat should minimise anterior displacement of the knee (16). The intention to restrict anterior displacement
of the knee and maintain a near vertical shin position is a key feature of the
movement strategies used by power lifters to perform the squat (16). To achieve this posture, many powerlifters adopt
a wide stance and focus on moving the hips posteriorly during the descent phase
of the movement (16). The reason is that maintenance of a near vertical shin position during the squat reduces internal forces at the knee and emphasises recruitment of the hip extensor muscles (4).
When national level power lifters were studied, it was reported that, when compared with the most successful squatters, less skilled squatters had a greater tendency to lean forward, thus developing greater trunk torque (10). Furthermore the more successful lifters also moved their knees anteriorly to a lesser extent during the squat, thus generating lower knee extensor torque (10).
Research by Fry et al., (2003) compared a restricted squat (knees unable to pass the toes) and an unrestricted squat. They found that there was a significantly higher amount of hip torque in the restricted squat due to an increased moment arm at the hips. This increased moment arm was due to a decreased torso angle relative to horizontal, thus maintaining the centre of mass over the base of support. In the unrestricted squat, there was a significantly higher amount of torque at the knee. Research by Escamilla et al., (2001) measured the differences in muscle activation during wide and narrow stance squats. It was concluded that there were no significant differences (8).
Athletes that have had ACL reconstruction or are ACLD (Anterior cruciate ligament deficient) are also advised to perform wide stance squats because of the increased translation forces at the knee in low flexion angles (13). Research by Miyaji et al., (2012) concluded that knee kinematics between the ACLD and contralateral intact knees are similar during a wide-based squat activity except at the low knee flexion angles. This further indicates that this activity is recommended for ACLD knees during pre-operative rehabilitation and potentially during the early post-operative phase as well (13).
When national level power lifters were studied, it was reported that, when compared with the most successful squatters, less skilled squatters had a greater tendency to lean forward, thus developing greater trunk torque (10). Furthermore the more successful lifters also moved their knees anteriorly to a lesser extent during the squat, thus generating lower knee extensor torque (10).
Research by Fry et al., (2003) compared a restricted squat (knees unable to pass the toes) and an unrestricted squat. They found that there was a significantly higher amount of hip torque in the restricted squat due to an increased moment arm at the hips. This increased moment arm was due to a decreased torso angle relative to horizontal, thus maintaining the centre of mass over the base of support. In the unrestricted squat, there was a significantly higher amount of torque at the knee. Research by Escamilla et al., (2001) measured the differences in muscle activation during wide and narrow stance squats. It was concluded that there were no significant differences (8).
Athletes that have had ACL reconstruction or are ACLD (Anterior cruciate ligament deficient) are also advised to perform wide stance squats because of the increased translation forces at the knee in low flexion angles (13). Research by Miyaji et al., (2012) concluded that knee kinematics between the ACLD and contralateral intact knees are similar during a wide-based squat activity except at the low knee flexion angles. This further indicates that this activity is recommended for ACLD knees during pre-operative rehabilitation and potentially during the early post-operative phase as well (13).
Squat Variation 2: Narrow stance/Full ROM
The full squat technique is common place in the
sport of Olympic weightlifting (11). It has been suggested
that deep squats could cause an increased injury risk of the lumbar spine and
the knee joints. Avoiding deep flexion has been recommended to minimize the
magnitude of knee-joint forces. Unfortunately, this suggestion has not taken the
influence of the 'wrapping' effect, functional adaptations and soft tissue contact
between the back of thigh and calf into account (11).
Based on biomechanical calculations and measurements of cadaver knee joints, the highest retro-patellar compressive forces and greatest compressive stresses are observed at 90 degrees (11). With increasing flexion, the additional contact between the quadriceps tendon and the intercondylar notch form to become the tendo-femoral support surface (wrapping effect) which contributes to enhanced load distribution and enhanced force transfer (11). Additionally, with further flexion of the knee joint, a cranial displacement of facet contact areas with continuous enlargement of the retro-patellar articulating surface occurs (11).
In terms of muscular development, research by Bryanton et al., (2012) showed that beneficial training of the knee extensors requires a full depth squat, but it can be trained at low relative intensity. The glutes and hamstrings responded best to full depth squats with high intensity barbell loads (around 90%) (3). Bloomquist et al., (2013) conducted research comparing the adaptations of heavy shallow squats and deep squats over twelve weeks. The deep squat group showed significantly higher thigh muscle cross-sectional area and superior changes in isometric knee extension strength (1).
Full depth squats have also been proven to increase jump height. Research by Domire & Challis (2007) and Hartmann et al., (2012) showed that deep front and back squats guarantee performance-enhancing transfer effects of dynamic maximal strength to dynamic speed-strength capacity of hip and knee extensors. Fry et al., (2003) found that squats past parallel are also healthier for your back due to the decrease in anterior trunk displacement. This means that in the full squat, lumbar shear forces are significantly decreased (10,15).
Based on biomechanical calculations and measurements of cadaver knee joints, the highest retro-patellar compressive forces and greatest compressive stresses are observed at 90 degrees (11). With increasing flexion, the additional contact between the quadriceps tendon and the intercondylar notch form to become the tendo-femoral support surface (wrapping effect) which contributes to enhanced load distribution and enhanced force transfer (11). Additionally, with further flexion of the knee joint, a cranial displacement of facet contact areas with continuous enlargement of the retro-patellar articulating surface occurs (11).
In terms of muscular development, research by Bryanton et al., (2012) showed that beneficial training of the knee extensors requires a full depth squat, but it can be trained at low relative intensity. The glutes and hamstrings responded best to full depth squats with high intensity barbell loads (around 90%) (3). Bloomquist et al., (2013) conducted research comparing the adaptations of heavy shallow squats and deep squats over twelve weeks. The deep squat group showed significantly higher thigh muscle cross-sectional area and superior changes in isometric knee extension strength (1).
Full depth squats have also been proven to increase jump height. Research by Domire & Challis (2007) and Hartmann et al., (2012) showed that deep front and back squats guarantee performance-enhancing transfer effects of dynamic maximal strength to dynamic speed-strength capacity of hip and knee extensors. Fry et al., (2003) found that squats past parallel are also healthier for your back due to the decrease in anterior trunk displacement. This means that in the full squat, lumbar shear forces are significantly decreased (10,15).
Summary
From the current research, unless the
athlete/client is anterior cruciate ligament deficient (ACLD) or is a
competitive power lifter who needs to brace positions and use partial ranges to handle extremely heavy competitive loads, then
full depth squatting is by far the healthier and smarter choice (provided the
athletes mobility allows them to meet the demands of the exercise). Every
aspect of physical training is catered for, whether it is hypertrophy, basic strength,
mobility or explosive power, utilising the full range of motion that joints are
designed for will always be best in terms of physical development and athleticism.
References
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