A Biomechanical Analysis of Back Squats: Motion Capture, Electromyography, and Musculoskeletal Modeling
Date of Award
Doctor of Philosophy (PhD)
Human Movement Sciences
Hunter J. Bennett
Joshua T. Weinhandl
Zachary A. Sievert
Previous literature evaluating maximal back squats have failed to identify key components of the study decisions and procedures that would allow for duplication. Firstly, the existence of a sticking region in maximally weighted resistance exercises is frequently discussed and has been described as a force-reduced transition phase between an acceleration phase and a strength phase of a lift. However, the etiology has yet to be agreed upon. Second, Electromyography (EMG) is frequently used to assess muscle activations. However, no best practice for EMG normalization has been proposed. Two methods are commonly implemented for normalizing EMG: a maximum voluntary isometric contraction (MVIC) and a dynamic maximum during the task being performed (DMVC). Finally, musculoskeletal modeling software has been increasingly utilized to evaluate muscle forces during weighted back squats. The quality of analyses of muscle forces, excitation, etc. are dependent upon inverse kinematics (IK). However, the methods used when examining IKs have also been short on details making duplication impossible.
This dissertation is in a multiple-article (n=3) format. The first two studies are published in refereed journals. These studies 1) determined the effects of load on lower extremity biomechanics during back squats, 2) examined the influence of normalization method on rectus femoris, vastus medialis, and biceps femoris activations during back squats, and 3) compared different inverse kinematic strategies for calculating hip, knee, ankle, and foot kinematics utilized in modeling of the back squat. For all studies, participants performed the NSCA’s one-repetition maximum (1RM) testing protocol. Three-dimensional motion capture (trunk, pelvis, and lower extremity), force dynamometry (force plates), and EMG were recorded during all squats.
The results of these studies found 1) vertical acceleration was a better discriminative measure than velocity for identifying the sticking region and there is a clear transition from knee to hip dominance for successful maximal squats, 2) the DMVC was more reliable and less variable than MVIC for normalizing EMG, and 3) creating a weld constraint between the foot and the floor results in the most closely matched foot kinematics to the DK results of the methods assessed.
These results indicate that 1) submaximum squats performed at increased velocities can provide similar moments at the ankle and knee, but not hip, as maximal loads, 2) significant emphasis on hip strength is necessary for heavy back squats, 3) normalization to DMVC is the superior method for weighted exercises, and 4) while the Weld model IKs most closely matched the foot DK results, the untenable ankle kinematics the Weld model produced demonstrated it might be the superior choice for modeling foot IKs, but not ankle IKs in maximally weighted back squats.
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Copyright, 2022, by Eva Maria Urdiales Maddox, All Rights Reserved.
Maddox, Eva M..
"A Biomechanical Analysis of Back Squats: Motion Capture, Electromyography, and Musculoskeletal Modeling"
(2022). Doctor of Philosophy (PhD), Dissertation, Human Movement Sciences, Old Dominion University, DOI: 10.25777/jkyy-ay36