Context: The single leg squat (SLS) is appropriate for targeting activation, strengthening, and/or neuromuscular retraining of the gluteus maximus, gluteus medius, and quadriceps. However, the effect of different non-stance leg positions on muscle activity has not been fully evaluated.

Objective: To compare the muscle activity of selected stance leg hip muscles during the SLS with 3 non-stance leg positions: in front, in the middle, and in back.

Design: Controlled laboratory study.

Setting: Biomechanics laboratory.

Participants: Seventeen healthy adults.

Main Outcome Measure(s): Surface EMG data of the gluteus maximus, gluteus medius, lateral hamstrings, medial hamstrings, rectus femoris, and TFL as well as kinetic data of the hip and knee were collected while participants performed the 3 SLS tasks. Mean muscle activation levels during the descent phase and ascent phase for the selected hip muscles were compared for the 3 tasks. Hip and knee kinetics in all 3 planes were also compared for the 3 tasks. Each variable of interest was analyzed using a separate linear regression model with a generalized estimating equations correction.

Results: Muscle activation levels of the gluteus maximus, gluteus medius, medial hamstrings, rectus femoris, and TFL on the stance leg during descent, and the medial hamstrings and TFL during ascent were significantly different between SLS tasks. The greatest number of differences occurred between SLS-Front and SLS-Back. During descent, gluteal muscle activity was greater in SLS-Front and SLS-Middle than in SLS-Back. For both phases, TFL activity was greater during SLS-Front than both SLS-Middle and SLS-Back. Kinetic differences at the hip and knee between SLS tasks were also observed.

Conclusion: The 3 SLS tasks have different muscle activation and kinetic profiles. Clinician and researchers can vary non-stance leg position during the SLS to manipulate muscle activation levels and tailor the exercise to assist with goals at different stages of rehabilitation.

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