# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 6 Basic Squat Biomechanics
As would be expected, the load-power relationship is different between front, back, and partial squats [67]. Although peak power during the concentric phase of back squats at various loads (20-90% of 1 RM) have not been shown to be statistically different, the optimal load for peak power output appears to be at loads of about 40-60% of 1 RM [96; 136; 137]. In a few studies [109; 137; 138], the optimal load was shown to be at ~30% of 1 RM, perhaps depending upon the type of athlete. However, peak and mean power output in these studies varied depending upon whether the power output was calculated for the load (bar + plates) [107; 136], the system mass [73; 96], or relative to the depth of the squat [137]. Additionally, in young women, measured leg press power may be similar or slightly greater than power calculations using the squat bar mass [139]. It seems logical that peak bar or system power production would occur at loads that are under 50-60% of 1 RM, because these loads allow generation of greater velocities. However, when examining athletic populations, the optimal load for the bar mass has been shown to range between approximately 40% and 70% of 1 RM for bar peak power [136; 137], with similar values for system mass [96; 110]. Strength-power athletes consistently produced optimum power outputs with higher relative loads [137]. This suggests that the optimum load range may differ with the method of training and level of strength development [110; 137]. However, as previously noted, the optimum load for force/velocity and therefore power production may be different at different joints [107; 108]. Thus, optimum production of force, velocity, and power appear to be best trained using a variety of loads and with a variety of conditions (non-ballistic versus ballistic). Linear kinetics, including joint reaction force through the knee (tibio-femoral and patello-femoral), can be a valuable method for analyzing force application in the lower extremities. Investigations concerning the magnitude (and rate) of force directed through anatomical structures may be critical to understanding movement and the potential for injury. Based on limited research, early reviews [19] indicated that greater knee flexion (deeper squat) increases stress in the knee ligaments and is potentially injurious. Although ligament stress does rise with greater knee flexion [140; 141], the tension that occurs during a full squat does not necessarily lead to damaged ligaments, such as the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), even with high external loads [17; 142; 143]. More details can be found in Section 7: Safety and Injury factors. Indeed, recent evidence indicates that it is possible that the stress of squatting on the knee, including parallel and full squats, could lead to beneficial alterations. Although the combination of partial and full squats may be advantageous [78], evidence indicates that full squats can result in greater structural and strength adaptations compared to partial squats [23; 31; 138]. Furthermore, it appears that the stimulus increases with movement velocity [75]. In their review, [PERSON] et al. [22] indicated that \"concerns about degenerative changes of the tendofemoral complex and the apparent higher risk for chondomalacia, osteoarthritis, and osteochondritis in deep squats are unfounded\". As a final analysis, correct squatting technique, appropriate progression, and properly periodized/programmed training can minimize the risk of knee injury and may strengthen connective tissue including ligaments. Kinetics (Angular kinetics): Angular kinetics deals with the causes of changes in the state of rotational motion (torques or moments of force). Inverse dynamics is a method for computing force or moments of force (torques), using a rigid body model. Calculation methods using such a model are based on the motion (kinematics) of a body and the body's inertial properties (mass and moment of inertia).