# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 6 Basic Squat Biomechanics
[20], using a low bar squat and three different foot stances (107 \(\pm\) 10, 142 \(\pm\) 12, and 169 \(\pm\) 12% of shoulder width), studied concentric velocities at the knee and hip. At near maximum loading, peak knee angular velocity occurred in the range of 110 to 130\({}^{\circ}\cdot\)s\({}^{-1}\) and the peak hip angular velocity occurred in the range of 102 to 122\({}^{\circ}\cdot\)s\({}^{-1}\)[20]. Importantly, the athletes studied (N = 39) were national powerlifting competitors typically using a low bar technique and compressive gear and represented a \"specific\" population [100; 106]. However, [PERSON] et al. [34], using American Football players (N = 10) as the study focus, investigated lower body kinematics during a high bar squat using much lighter loads (25% of 1 RM). They reported a similar angular velocity of the knee and hip, ranging from 113 to 120\({}^{\circ}\cdot\)s\({}^{-1}\) at the knee and 114 to 117\({}^{\circ}\cdot\)s\({}^{-1}\) at the hip. It is important to note that peak ankle, knee, and hip angular velocities or power outputs do not necessarily occur at the same absolute or relative bar load, particularly in ballistic movements such as loaded jumps [107; 108]. This observation has important variation ramifications for training loads, suggesting a spectrum of loads be used to ensure \"optimum\" velocity and power training of all three joints. The vertical velocity of a system (lifter plus barbell) is often calculated using the center of mass (CoM) displacement. Although concentric velocity (and power) calculated from CoM and the bar are similar, depending upon the sport, velocity (and power) may be more appropriately calculated from the bar, particularly for strength power athletes using implements (e.g., throwers, weightlifters, powerlifters) [109; 110]. Indeed, the bar velocity is easier to quantify compared to tracking the movement of CoM of the system for a number of reasons. Typically, the location of the CoM is established with the use of video motion (kinematic) analysis and requires the use of a full-body marker set. While this process is well established, it is time consuming and requires specialized laboratory equipment. However, placing a marker on the barbell during squatting movements allows for sagittal plane analysis of barbell displacement and velocity in a more time-efficient and effective manner, particularly when frequent measurements are necessary. This method of analysis has been used in several studies investigating bar velocity to analyze explosive effort during the concentric phase of the back squat [96; 111]. More recently, methods of analyzing bar velocity (and displacement) have included the use of linear position transducers [112], accelerometers, or inertial movement sensors [72; 111; 113; 114] that are attached to the bar or a combination of linear potentiometers, and force plates that can be used to analyze a variety of kinetic and kinematic characteristics and derivations including power output [72; 95]. During the ascent phase, average bar velocity typically ranges from approximately 0.97 to 0.54 m s\({}^{-1}\) using 20% to 90% of 1 RM back squat [96]. Obviously, compared to lighter loads, heavy loads, particularly near maximum loads, can substantially reduce the bar velocity and power output [71; 73]. Indeed, a faster bar velocity can markedly influence the average and peak power output of the lift. Additionally, bar velocity can be affected by fatigue and the loss of bar velocity may represent a method of quantifying acute or chronic fatigue [95]. Furthermore, it is important to produce a high RFD in the concentric (ascent) phase to emphasize \"explosiveness\" during the squat. From this perspective, the importance of analyzing bar velocity and RFD specifically for explosiveness becomes apparent. Although there is a specific emphasis on pushing the bar as hard as possible during the concentric phase, for heavy loads, relatively constant and relatively slow bar velocity indicates the \"control\" aspect of the lift in the eccentric (descent) phase.