Hip and knee frontal plane kinematics are not associated with lateral abdominal muscle thickness and trunk muscle endurance in healthy men and women

Lateral trunk muscles may contribute to the excessive ipsilateral trunk lean, which is a mechanical alteration related to impairment in hip and knee kinematics. This study aimed to investigate if hip and knee kinematics, lateral abdominal muscle thickness, and trunk muscle endurance are associated differently in men and women. Forty-six participants (27 men and 19 women) completed the following assessments: (1) lateral abdominal muscles thickness [external oblique + internal oblique + transversus abdominis] measured with ultrasound; (2) hip adduction (HADD) and knee frontal plane projection angle (FPPA) during single-leg squat; (3) muscle endurance in the side plank test. We did not find significant associations between HADD and lateral abdominal muscle thickness (men: r = 0.205; p = 0.315; women: r = 0.358; p = 0.145) or side plank time (men: rs = − 0.102; p = 0.614; women: rs = 0.391; p = 0.098). Moreover, no significant associations were found between FPPA and lateral abdominal muscle thickness (men: r = 0.012, p = 0.953; women: r = 0.326, p = 0.186) or side plank time (men: rs = 0.087, p = 0.667; women: rs = 0.319, p = 0.184). A strong association between lateral abdominal muscle thickness and muscle endurance was found only in women (r = 0.683; p = 0.002). Hip and knee kinematics were not associated with lateral abdominal muscle structure or endurance in men and women. Muscle structure seems to be associated with time to exhaustion in a side plank test only in women.