Effect of Visual Input and Foam Rubber on Leg-Joint Angles and Sway of Center of Pressure during Stepping on the Spot

Dynamic balance has frequently been evaluated by using center of pressure (COP) during stepping movement. COP sway may be greater during stepping on foam rubber, which is a kind of external load. This study aimed to examine the effect of leg-joint angles and COP sway during stepping on a spot in 13 young male adults (mean age 25.6 ± 4.8 years, mean height 170.6 ± 5.2 cm, mean mass 69.1 ± 8.2 kg), with or without foam rubber and with eyes open or closed. When subjects stepped on foam rubber placed on two force plates (right and left), while matching a tempo of 100 bpm for 20 s under the above four conditions, characteristics such as mean angles of hip, knee, and ankle joints and COP sway were measured. In the results of two-way ANOVA (rubber condition × eye condition) and post-hoc tests, the hip-joint angle was significantly greater with eyes open, regardless of with or without foam rubber. The knee-joint angle was significantly greater in eyes closed with off-foam-rubber than on-foam-rubber. The ankle-joint angle was significantly greater in offfoam-rubber, regardless of eyes open or closed, and with eyes open than with eyes closed, regardless of with or without foam rubber. The total trace length and velocity were significantly greater in off-foam-rubber with eyes open, and on-foam-rubber with eyes closed than on-foam-rubber with eyes open. The other sway parameters were significantly greater with eyes open than with eyes closed regardless of with or without foam rubber. The hip-joint angle was significantly greater with eyes open regardless of with or without foam rubber. In conclusion, the COP sway during stepping with a stipulated tempo is less with eyes open than eyes closed, but the motion of knee and ankle joints is greater with eyes open. The sway distance and velocity during stepping with eyes open and motion of knee and ankle joints during stepping with eyes closed are both affected by the foam-rubber load. When stepping on the foam rubber, movement of the knee joints relates to distance and velocity of COP regardless of open or closed eyes. The findings in this study will be used to evaluate balance functions that are closely related to basic movements.