|dc.description.abstract||Purpose: The primary purpose of this research was to compare barbell deadlifts and squats, as
well as two technique variations within each lift, for their effects on lumbar spine kinematics and kinetics. The techniques compared within the deadlift condition were the low-hip deadlift (LHDL) and the high-hip deadlift (HHDL). The techniques compared within the squat condition were the high-bar squat (HBS) and low-bar squat (LBS). The outcome variables measured were peak lumbar flexion, L4-L5 and L5-S1 moments, and L5-S1 joint reaction force.
Methods: Data were collected and reported on 17 healthy competitive strength athletes (male = 12, female = 5, age = 26.5 ± 4.7 years, height = 176.1 ± 4.6 cm, body mass = 97.7 ± 22.3 kg). Participants completed three single lifts at 85% of their estimated one-repetition maximum using each lifting technique during a single session. Data were collected using an 8-camera 3D motion capture system and two in-ground force plates then processed using custom Matlab routines. Lumbar flexion was calculated using a custom kinematic driven lumbar spine model. Joint moments were calculated using inverse dynamics. Joint reaction force calculations were based on an equilibrium approach using a single-equivalent muscle model. A 2×2 factorial ANOVA with the factors of lift type (deadlift vs squat) and bar position (anterior vs posterior) was used to determine the effect of each main lift on the outcome variables. Significance for the ANOVA was set at p<.01. Planned paired samples t-test’s were used to compare the effects of lift technique (LHDL vs HHDL and HBS vs LBS) on the outcome variables. Significance was set at p<01.
Results: Peak lumbar flexion, expressed as a percentage of maximal voluntary flexion, was significantly greater during the deadlift condition (76.76 ± 16.07%) in comparison to the squat condition (64.2 ± 19.8%, p = .005). Within the squat condition, peak lumbar flexion was significantly greater for the LBS technique (67.9 ± 19.7%) when compared to the HBS technique (60.43% ± 19.79, p<.001). Normalized L5-S1 joint reaction force results displayed that within the deadlift condition, there was significantly greater average shear force during the LHDL technique (2.02 ± 0.23N) in comparison to the HHDL technique (1.98 ± 0.22N, p=.004). Within the squat condition, there was significantly greater peak shear force during the HBS technique (2.59 ± 0.42N) in comparison to the LBS technique (2.47 ± 0.40N, p<.001). Significant differences were not observed between or within lifting conditions for any of the other variables.
Conclusion: This is the first study to directly compare lumbar flexion and L5-S1 joint reaction forces between the barbell deadlift and squat, as well as the HHDL/LHDL and HBS/LBS technique variations within each lift. Results suggest that if normalized to barbell load, barbell squats create equivalent loading at the L5-S1 joint when compared to the deadlift. They also suggest significant differences in peak lumbar flexion and peak shear joint reaction force when comparing the HBS and LBS. Past research on barbell squat kinematics have perpetuated the assumption that the torso remains relatively rigid during this exercise; however, these findings indicated the lumbar spine undergoes considerable flexion when squatting to a depth slightly below parallel. Furthermore, the amount of lumbar flexion taking place seems to be influenced by the squat technique used and this can lead to significant differences in peak L5-S1 shear joint reaction force, a variable believed to be related to low back injury.||