Date of Award

August 2018

Degree Type

Thesis

Degree Name

Master of Science

Department

Kinesiology

First Advisor

Jennifer E Earl- Boehm

Committee Members

Wendy E Huddleston, Kyle T Ebersole

Keywords

Barbell Back Squat, Biomechanics, Kinematics, Squat Mechanics, Support Moment, Weightlifting

Abstract

INTRODUCTION: The strength implications of the barbell back squat make it ideal for use in training programs, rehabilitation, and competition. Even though the back squat is an integral part of these programs, there are also concerns about injury risk due to improper biomechanics. Restricted squats (knees kept behind the toes) are noted to reduce joint loading at the knees but may not take into account added potential risks for the entire lower extremity. Unrestricted squats are more representative of natural movement patterns but may increase joint loading especially at the knees. Research has explored the biomechanics of back squats in elite, male populations, but has yet to investigate how back squat biomechanics differ between restricted and non-restricted squats in a female, recreationally-active population. PURPOSE: Therefore, the purpose is to determine how restricting the anterior movement of the knees during barbell back squats affects joint mechanics of the lower extremities in female recreational weightlifters. METHODS: 16 healthy, female, recreationally-active, weightlifters (mean  SD, age= 25.6 4.2 yrs; height= 170.4  8.3cm; weight= 63.8 8.3 kg) participated in this study. Biomechanical analysis of joint angles and moments were performed using a 3-D motion capture system and standard procedures (Motion Analysis Corporation, Santa Rosa, Ca). Participants performed 5 squats for each of the three squat conditions; natural (NS), knee over toe (KOT), and restricted (RS). The middle 3 squats were used for data processing. A repeated measures ANOVA was used to compare sagittal plane joint angles, lower extremity joint moments, net support moments, and the relative contribution of the individual joint moment to the net support moment, expressed as a percentage. An adjusted alpha value of α < .004 determined statistical significance. RESULTS: Knee angle and flexion moment were smaller in RS condition and larger in the NS condition F(2,30)=35.3,p<.0001, F(2,30)=18.8,p<.0001. Hip extension moment was smallest in KOT and largest in the RS and NS conditions F(2,30)=18.2,p<.0001. Ankle angle was the smallest in RS and NS conditions and largest in the KOT condition F(2,30)=75.8,p<.0001. Trunk angle was largest in the RS condition F(2,30)=42.5,p<.0001. The net support moment was largest in the NS condition F(2,30)=7.9,p=.002 CONCLUSIONS: The primary findings of this study supported initial hypotheses that anterior restriction of the knees during a barbell back squat affects lower extremity biomechanics. There were clear differences in sagittal plane joint angles and joint moments seen across the NS, KOT, and RS conditions. The net support moment and the percent contribution of the joint moments also differed between squat conditions and provided valuable information about the distribution of the load across the joints among the three squat conditions. Findings also revealed that this population has natural squat mechanics that are most similar to squatting with the knees over the toes. This may suggest that individuals in this population, with a year of barbell back squat experience, self-optimize their natural squat mechanics. Alternatively, it is possible that the three squat conditions could all be appropriate ways to squat, depending on the goals of the lifter. These three squats may be used as a way to decrease the load on individual joints while performing the barbell back squat. Training may also be important to decreasing the compensations seen in the RS condition, which may allow for lifters to squat in a safer manner without disproportionally increasing joint loading.

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