Lower trunk muscle activity-induced alignment and cop position during single-leg standing.

[Purpose] The purpose of this study was to clarify fundamental changes induced by lower trunk muscle contraction during single-leg standing. [Subjects and Methods] Ten healthy normal males participated in this study. All subjects could accurately perform lower trunk muscle contraction-type Abdominal Expansion (AE), Abdominal Bracing (AB), and Abdominal Cave-in (AC). The alignment and position of the center of foot pressure (COP) during single-leg standing with SLR and step position after rotating the body from single-leg standing with maximum SLR were measured in each lower trunk muscle contraction type. [Results] When AC was performed during single-leg standing with SLR, the SLR angle increased, COP shifted backward, and the posterior tilt angle of the trunk and cross step distance decreased. [Conclusion] It was assumed that AC during wind-up increases the angle of lower limb elevation and decreases the posterior tilt angle of the trunk and cross step distance.