Core muscles thickness is not associated with knee frontal plane projection angle during single-leg squat in healthy people

Background: Core muscles play an important role in lower limb stability and alignment, with their weakness being associated with poor alignment and, consequently, with injuries. Despite muscle structure being critical to muscle strength production, we did not find studies associating the morphology of the core muscles and lower limb alignment during functional tasks. Research question: Is there association between thickness of core muscles (external oblique - EO, internal oblique - IO, transversus abdominis - TrA and gluteus medius - GMed) and lower limb alignment during the single-leg squat in healthy subjects? Methods: Forty-six healthy participants (27 male and 19 female) performed the following evaluations: (i) measurements of muscle thickness of the EO, IO, TrA and GMed using ultrasound and (ii) measurements of lower limb alignment using the knee frontal plane projection angle (FPPA) during the single-leg squat. A Spearman rank correlation coefficient (r(s)) was performed between the thickness of selected core muscles (OE, OI, TrA and GMed) and the knee FPPA. In addition, a partial correlation (r) was performed, using sex, physical activity level and body mass index as control variables. Results: We did not observe significant correlations between the knee FPPA and the thickness of the EO (r(s) = 0.194; p=0.197), IO (r(s)=0.182; p=0.225), TrA (r(s)=0.073; p=0.627) and GMed (r(s)=-0.092; p=0.542). When controlling for sex, physical activity level and body mass index, similar results were observed [EO (r = 0.157; p = 0.316), IO (r = 0.261; p = 0.092), TrA (r = 0.030; p = 0.850) and GMed (r = -0.144; p = 0.356)] Significance: Our results demonstrated that core muscles' thickness is not associated with lower limb alignment during the single-leg squat in healthy people.