Changes in Weight Distribution and Subsequent Biomechanical Characteristics Across Starting, Transitional, and End Phases of the Back Squat in Healthy Adults



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The back squat is a common exercise used in strengthening and conditioning as well as activities of daily living. Purpose: Determine weight distribution in all phases of the back squat, kinematics and muscle forces of the vastus lateralis and vastus medialis at the starting, transition, and end points of the exercise. Methods: 27 healthy, asymptomatic individuals volunteered to participate in performing back squats for the study. Height (cm), weight (kg), Q-angle, and shoulder width were measured before the back squat was performed. They then completed 3 sets of 3RM and 5 sets of 1 repetition at 65 percent of their 3RM. Data was recorded during the squats using the TekScan HR mat, EMG surface electrodes, and electric goniometers. Results: Sample t test revealed significant weight shift on the left side compared to the right across all phases of the back squat (p<.05). Weight distribution on the right was significantly different among the three phases (F2,50=5.091, p=0.010), and the end phase was significantly lower than the transitional phases on the right side (p=0.024). Weight distribution was significantly different during all three phases on the left (p=0.002, F2.50= 6.772) and significantly higher at the end phase on the left side (p=0.010). Vastus medialis and lateralis muscle force increased significantly during ascending phase. Conclusion: These findings suggest that the transition phase is the most important phase of the squat in terms of maintaining consistency with weight shift, and that weight distribution is not necessarily equal between lower extremities even in a healthy, asymptomatic population. This study lends itself to future studies focusing on symptomatic participants as well as further definition and study of the transitional phase of the back squat.



back squat, asymmetrical weight shifting