2018 Volume 16 Issue 2 Pages 51-59
We investigated postural control during a knee flexion-extension exercise. Twelve healthy young adults performed the exercise at a preferred speed with the following knee flexion angles (KFA): 5, 10, 20, 30, 40, 50, 60, 70 and 80 degrees. The center of pressure in the anteroposterior direction (CoPap) and the movement angle of the knee, inclination angles of the trunk and lower leg, and muscle activity of the rectus femoris (RF) were measured. In each KFA, ten cycles were adopted for analyses. For CoPap, the mean position and peak amplitude at a lower frequency than the knee exercise were maintained within a certain narrow range, regardless of the KFA. At a KFA of 5-30 degrees, the trunk was kept vertical but at a KFA of 40 degrees or higher, the trunk was leaned forward, with the mean position of the CoPap shifted forward slightly. It was presumed that the forward leaning of the trunk would inhibit an excessive increase in RF muscle activity. At a KFA of 50 degrees or higher, however, the forward shift in the mean position of the CoPap to maintain whole-body balance was restricted. At a KFA of 5 degrees, the mean position of the CoPap shifted slightly backward. The backward shift may relate to the enhancement of sensory information during knee flexion with the increase in RF activity. These results indicate that the targets of postural control change according to the KFA.
