# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 6 Basic Squat Biomechanics
Finally, electromyography (EMG) analysis is a necessary approach for examining neural activation of the muscles associated with variations of load, foot position, and stance width that can be used during various types of squatting movements [32; 66; 82; 86]. In recent years, comprehensive studies using various combinations of motion capture videography, force plates, and EMG for squat analysis have increased in number. The increased interest in exploring the biomechanical aspects of the squat suggest that to truly understand the intricacies of squatting movements, a comprehensive understanding of the mechanisms associated with the neuromuscular components of squat performance is required. The primary focus of these studies has dealt with understanding the nature of the mechanistic contributor(s) during a squat. At the same time, there has been a more recent trend of investigation dealing with the prediction of injuries based on the biomechanical findings. In the following section of this paper, further biomechanical reports dealing with a more detailed discussion of kinematics, kinetics, and EMG are discussed. Kinematics: Kinematics deals with the characteristics that result from force application (kinetics), such as displacement and velocity. From a human factor standpoint, both joint and segmental kinematics are commonly reported variables in research directly exploring the squat (Figure 1). Typically, the sagittal plane is used as the plane of reference when performing a kinematic evaluation of squatting movements. This type of analysis is typically used to determine joint angles, joint and segmental displacement, and velocity. Squatting characteristics (e.g., depth, trunk lean etc.) can be markedly affected by differences in anthropometrics and tissue structure. These include characteristics such as sex differences. Examinations of various types of squats have clearly indicated that sex-specific kinematic differences are present [103; 104]. Both male and female subjects  
Figure 1: Diagram of kinematic variables measured during squat. (**a**) Trunk, (**b**) hip, (**c**) thigh, (**d**) knee, (**e**) shank, and (**f**) ankle. displayed marked hip, knee, and ankle deviations. However, in the back squat, males, compared to females, displayed smaller hip and knee flexion angles with all external loads (ranging from zero to body mass + 50%) [105]. Furthermore, increasing external loading resulted in ankle joint dorsiflexion to a greater degree in males in order to compensate for the lost RoM from the hip and knee [103]. Additionally, knee displacement was forward and shin angle was diagonal rather than vertical, which ultimately relates to greater ankle dorsiflexion, assuming the entire soles of the feet remain in contact with the floor [103]. An interesting finding from the same study was that females displayed somewhat different squat kinematics demonstrating less knee forward displacement. This may indicate that they were using a marked forward trunk lean, or possibly exhibited greater flexibility in the hip and knee joints, resulting in a minimization of the forward movement of the knee without having a greater degree of dorsiflexion. Additionally, there were sex specific timing differences, with the males reaching maximum forward knee displacement at 84% of their maximum descent, while females achieved maximum knee displacement at 93% of their maximum descent [103]. These differences in joint flexion and extension likely affect the ability to generate forces and subsequent velocity of movement. When focusing specifically on the lower extremity joints, knee and hip angular velocities influence vertical concentric velocity [20]. If the focus of training is to generate high rates of force development (RFD) and power output during the concentric action, faster knee and hip extension velocities are required in order to create these characteristics. For example, [PERSON] et al.