Postural stability effects of random vibration at the feet of construction workers in simulated elevation
The risk of falls from height on a construction site increases under conditions which degrade workers postural control. At elevation, workers depend heavily on sensory information from their feet to maintain balance. The study tested two hypotheses: sensory enhancement  sub-sensory (undetectable) random mechanical vibrations at the plantar surface of the feet can improve workers balance at elevation; and sensory suppression  supra-sensory (detectable) random mechanical vibrations can have a degrading effect on balance in the same experimental settings. Six young (age 2035) and six aging (age 4560) construction workers were tested while standing in standard and semi-tandem postures on instrumented gel insoles. The insoles applied sub- or supra-sensory levels of random mechanical vibrations to the feet. The tests were conducted in a surround-screen virtual reality system, which simulated a narrow plank at elevation on a construction site. Upper body kinematics was assessed with a motion-measurement system. Postural stability effects were evaluated by conventional and statistical mechanics sway measures, as well as trunk angular displacement parameters. Analysis of variance did not confirm the sensory enhancement hypothesis, but provided evidence for the sensory suppression hypothesis. The supra-sensory vibration had a destabilizing effect, which was considerably stronger in the semi-tandem posture and affected most of the sway variables. Sensory suppression associated with elevated vibration levels on a construction site may increase the danger of losing balance. Construction workers at elevation, e.g., on a beam or narrow plank might be at increased risk of fall if they can detect vibrations under their feet. To reduce the possibility of losing balance, mechanical vibration to supporting structures used as walking/working surfaces should be minimized when performing construction tasks at elevation.
vibration sensory suppression fall prevention balance control