# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 6 Basic Squat Biomechanics  
In an effort to better understand the underlying mechanisms associated with the squat, the biomechanics of the barbell back squat were originally investigated in elite level athletes nearly five decades ago [88; 89]. A major reason for this approach was to obtain normative data on elite strength athletes. At that time (the 1970s), the primary available resource for performing a biomechanical analysis of any human motion was to employ techniques limited to the examination of only one plane of movement. Shortly after the initial video analyses, the integration of force plates in the biomechanical assessments of the squat began to be used [90]. Typically, this approach was undertaken to determine kinetic and kinematic information about the squat. Inverse dynamics were employed when examining joint kinematics [91]. With these approaches, investigators established a baseline of biomechanical characteristics for the barbell back squat. Although motion capture technology has advanced well over the last forty years, squat mechanics are still being analyzed largely in the sagittal plane because of the anterior-posterior movement that primarily occurs at the trunk and the joints of the lower extremities [19; 92; 93]. In the back squat, a typical RoM for an experienced lifter would require ankle dorsiflexion of about 20 to 25\({}^{\circ}\), knee flexion to an internal angle of 95\({}^{\circ}\) in a half squat and approximately 60\({}^{\circ}\) in a parallel squat, and flexing the hip to a range of 85 to 110\({}^{\circ}\) as a lifter reaches the peak descent position [34; 43; 46; 66; 68; 88]. Of importance from both practical and analytical standpoints is squat symmetry. Observation suggests that both sides of the kinematic squat sequence are similar [34; 46; 88]. [PERSON] et al. [94] examined the squat 30 \(\pm\) 12 weeks after ACL reconstruction and indicated that during a high bar squat, lower extremity RoM on both legs was relatively similar with less than a 3\({}^{\circ}\) difference between each side of the body for the three joints (ankle, knee, and hip) examined. It is possible that a difference of \(\geq\)3\({}^{\circ}\) in RoM between the right and left sides of the lower extremity joints could be indicative of a potential asymmetry that could be a cause for some concern. However, from a practical performance analytical point of view, a \(\leq\)3\({}^{\circ}\) difference in RoM between the right and left sides of the body would be difficult to visually capture and is usually considered to be of limited importance during the analytical process. Another measurement approach is to collect kinetic measures using individual or multiple force plates in order to examine force production and power output during squatting [39; 62; 95; 96]. More detailed analyses of the squatting movement can be performed when synchronizing video (2D or 3D) cameras with a force plate [97; 98]. Researchers have used this technique in order to analyze lower extremity joint kinetics and kinematics [19; 97]. Indeed, joint kinetics analyses have been undertaken to understand the mechanical loads in the lower extremity joints as well as the lower back region [39; 46; 82; 89; 95; 97; 98]. Typically, the greatest lower extremity joint torque, but least external applied force, occurs shortly after the initiation of the ascent phase of the squat at what has been termed the \"stickingpoint\" or \"sticking region\" [19; 34; 80; 99; 100]. Other kinetic variables such as compression and shear forces at the knee have been reported in scientific literature because of their clinical relevance [19; 39; 81; 101]. Obviously, a loaded barbell back squat creates a greater amount of compressive force (and shear force) on the spine as compared to a body weight squat. As a result of placing the loaded barbell on the upper back, the joint force at the lumbar region becomes the largest among the joints in the lower half of the body [102].