# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 6 Basic Squat Biomechanics
For example, analogies can be made from the sport of weightlifting, in which excessive frontal and transverse plane movements during a pull are considered faulty mechanics [127; 128; 129]. Several researchers [129; 130] have stated that these faulty motions can lead to unsuccessful life attempts, and less barbell displacement asymmetry between the left and right sides increases the chance of a successful lift in weightlifting competitions. Although the movements are different between the squat and weightlifting, minimizing unwanted lateral tilt and rotation of the barbell has been noted as an effective way to improve squat performance [131; 132; 133]. It should be, again, noted that during powerlifting or the low bar squat, in which the bar is lower on the shoulders/back, there is more anterior lean of the trunk, particularly if the foot stance is relatively narrow [41; 46]. This position can place considerably more stress on the lower back compared to the high bar squat [46]. However, lower back stress can be reduced by two factors. Firstly, the bar is lower on the back, which shortens the moment of the arm relative to the lower back, and thus hip torque can be reduced compared to a high bar squat at the same load and degree of trunk tilt. However, lower back stress can be higher in a low bar squat when the two squats are performed in actual training, because many athletes are able to use heavier absolute loads with a low bar squat and there is typically a greater degree of trunk forward tilt with a low bar squat. Secondly, a wider stance can provide a mechanism which would allow the hips to move forward, allowing the lifter to \"sit up\" and thus creating a more erect trunk and consequently reducing the moment arm and lower back strain [41]. Kinetics: Linear kinetics deals with the causes of change in the state of linear motion. When measuring kinetic values during squatting tasks, ground reaction forces (GRF) are typically measured using a single force plate that allows examination of both legs, or dual force plates allowing examination of forces produced by each side of the body independently [96; 110; 134]. The ability to assess vertical GRF allows for a more comprehensive examination of the force-time characteristics associated with squatting movements. Logically, GRF (and impulse) will increase with higher loads. Although it is clear that higher loads increase the GRF, few investigators have specifically examined the relationship between the peak or average GRF and various loads [96; 110]. System CoM acceleration is reflected by the pattern of concentric GRF during the squat. For example, [PERSON] et al. [96] reported that a double peaked GRF occurred (1) during the initial phase of concentric action and (2) immediately after passing the sticking region during back squats performed with high bar squat loads ranging from 20-90% of 1 RM squat. These peaks in force correspond to brief periods of acceleration; an initial acceleration occurs during the transition from the descent (eccentric action) into the ascent (concentric action) phase of the movement, and another acceleration occurs in the latter part of the ascent phase near the finish of the lift. This later acceleration possibly occurs as a result of the hips and knees moving forward, placing the lifter at a stronger mechanical advantage. Both [PERSON] et al. [88] and [PERSON] [20] demonstrated a double peak in the same phase of ascent velocity for powerlifters using a low bar squat. Because the barbell velocity is related to GRF and acceleration, it is expected that there would be two velocity peaks during the concentric phase. This appears to be particularly evident when heavy loads are used [96]. Thus, it appears that two GRF peaks occurring during the ascent phase is a normal characteristic of full or parallel squat kinetics. Understanding the load-power relationship during squatting movements is essential for establishing an understanding of potential optimal load(s) for peak power production, as well as potential injury reduction [135].