The effects of foam surface properties on standing body movement.

Conclusion. The properties of a foam surface significantly affect body movement variance. Therefore, studies where different kinds of foam have been used may not provide congruent results. Objectives. To investigate whether different properties of foam affect body movement variance (32 subjects, mean age 22.5 years) in terms of linear head, shoulder, hip and knee movements. Subjects repeated tests with eyes open and closed, to also determine the effect of vision on the different surfaces. Subjects and methods. Body movement was captured on three different foam surfaces and on a control solid surface over 2 min using a Zebris™ ultrasound measuring system. The foam surfaces were categorized by their firmness as firm foam, medium foam and soft foam. Results. Body movement variance increased significantly when standing on all foam surfaces compared with the solid surface. However, movement variance was larger when standing on the firm foam compared with the softer foams, except in the anteroposterior total and low frequency ranges. We also found that the body movement pattern differed when standing on foam and firm surfaces, with greater reliance on movements at the knee to give postural stability on foam than on the solid surface. Vision clearly reduced all body movement variances, but particularly within the high frequency range.