Not all single leg squats are equal: a biomechanical comparison of three non-stance leg positions
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The single leg squat (SLS) is a functional movement task that is commonly used by clinicians as both an evaluation and treatment tool. Across clinics and research labs, no standard SLS procedure exists and variations in non-stance leg position are typical. There is little information to guide clinicians in selecting the appropriate SLS variation for individual rehabilitation goals. Non-stance leg positioning during the SLS may influence lower extremity mechanics and muscle activity. It is unknown if, and to what extent, altering the non-stance leg position during the SLS affects how the SLS is performed. The purpose of this dissertation was to examine how healthy adults performed the SLS when asked to place their non-stance leg in 3 commonly used positions during the squat. We hypothesized that the position of the non-stance leg would have a nontrivial impact on how the SLS was performed and result in different stance leg mechanics and muscle activation levels. Sixteen females participated in Study 1, the same 16 females from Study 1 and 16 males participated in Study 2, and 17 adults (with some overlap of participants from Study 1 and Study 2) participated in Study 3. Kinematic data were recorded using a motion capture system, ground reaction force data were collected using the force plates in a split-belt instrumented treadmill, and muscle activity levels were quantified using a surface electromyography system. Results from all 3 studies supported our hypothesis. Study 1 indicated that different non-stance leg positions during the SLS affected the kinematics at the trunk, pelvis, and lower extremity and the lower extremity kinetics in females. Study 2 demonstrated that males also exhibited different kinematics and kinetics for the 3 SLS tasks with different non-stance leg positions. In addition, females and males performed the 3 SLS tasks differently, suggesting that they respond differently to altering the non-stance leg position. Study 3 indicated that hip muscle activation levels were affected by the non-stance leg position during the SLS. Our results suggest that clinicians and researchers should be mindful of the non-stance leg position during the SLS and be cautious of using SLS variations interchangeably.