# The Use of Free Weight Squats in Sports: A Narrative Review--Terminology and Biomechanics
## 7 Safety and Injury Factors
[161], using 3D motion analysis, studied experienced lifters, and showed little influence on spinal movements from a kinematic perspective when using a belt with increased loading; hyperextension occurs with or without a belt [161]. However, other studies showed contradictory results: a belt may provide some support to back position by increasing the activation of supporting muscles, increasing intra-abdominal pressure, and stiffening the trunk, which may enhance squat performance [177; 178; 179]. It is well-documented that increased intra-abdominal pressure created by a Valsalva or semi-Valsalva technique can serve as a significant support mechanism for the spine [180; 181; 182; 61; 183; 184; 185; 186; 187; 61]. A potentially beneficial function of belts may be to assist in raising intra-abdominal pressure and lowering compression forces on the lumbar vertebrae [178; 180]. This is related to the importance of using mid-section musculature to assist in maintaining an appropriate stable spinal alignment in a normal curvature, or in a lordotic position independent of belts, to help minimize anterior-posterior shifts of the trunk during the squat. Although specific mid-section exercises can be beneficial for trunk/spine stabilization, data indicates that large muscle mass, multi-joint exercises transmitting forces through the mid-section, such as squats, likely play an important role in improving the stability of the mid-section [183; 164; 152]. For example, evidence indicates that large muscle mass, multi-joint exercises can activate a number of mid-section muscles to a greater degree than typically performed isolated or unstable mid-section exercises, such as the superman and pelvic thrust on a stability ball [183; 152]. Furthermore, as previously noted, an erect (stable) spine is advantageous for squatting, as excessive trunk flexion creates greater shear forces, and excessive hyperextension or flexion creates an uneven load on the vertebral body in multiple directions [102]. Compression and simultaneous extension or rotation of the spine, particularly the lumbar spine, can cause increased compression in the posterior annulus compared with neutral loading [161]. However, injury potential can be greatly reduced through changes in hip joint angle during the squat [22]. Forward leaning during squatting increases the potential for flexion of the lumber spine [22]. Because of the combination of high axial compression plus shear forces, ventral (forward) flexion can increase the risk of disk herniation [53]. The effects of ventral flexion can be minimized by creating a strong lumbar extension during motion reversal (initiating concentric action). Lumbar extension is created and maintained by increased lumbar erector spinea muscle activity and results in closing of the apophyseal joints and reducing shear force on the discs [22]. Although analyzing cervical spine (C-spine) compression would be valuable, a solid body of literature regarding this topic has not been established. Specifically, when considering the bar placement for a high bar squat, the bar is centered across the shoulders just below the spinous process of the C-7 vertebrae [52; 105]. For a low bar squat, the bar sits further down the back, often on the superior portion of the scapula across the middle trapezius and rhomboid muscles regions. Currently, neither placement has been identified as a cause of substantial injury among individuals performing squats regularly. Considering this discussion, along with proper loading progression, (1) performing squat exercises with correct technique specifically by maintaining a stable spinal position throughout the squat, and (2) appropriate use of a Valsalva or partial Valsalva technique to help maintain appropriate intra-abdominal pressure may assist in preventing back injuries that potentially result from squat exercises. Practitioners should be aware that if one of these factors is deficient or lacking, the risk of developing a lower back injury and pain may increase.