Nonlinear behavior of the center of pressure in simulated standing on elevated construction beams.

This study investigated the effects of width of construction beams and single-hand load holding task conditions on nonlinear behavior of the foot center of pressure (COP) exerted on the beam. The foot COP, defined as the point of application of the result of vertical forces acting on the surface of foot support, was measured in the lateral direction under simulated standing task conditions. Twelve healthy male subjects were asked to hold a load of 6.8 kg and 11.3 kg while standing on the elevated construction beams with widths of 10 and 22.5 cm (4 and 9 inches, respectively) under low and high foot separation (foot step). The results showed that both beam width and single-hand load carrying conditions had significant effects on the observed nonlinearity of the foot center of pressure exerted on the beam. Standing on the narrow beam resulted in higher level of chaotic behavior of COP compared to the wide beam condition. The nonlinearity of the COP exerted by the forward (left) foot was higher for the narrow beam condition. For both beams, the nonlinearity of the COP exerted by the forward (left) foot was consistently higher than the COP exerted by the backward (right) foot. Furthermore, for both beams, single-handed holding of the 11.3 kg load resulted in higher levels of COP nonlinearity than carrying 6.8 kg or no load at all. The study results indicate that nonlinear dynamics behavior of the forward foot under single-handed high load holding condition may be critical to preserving lateral stability during standing at the construction beams.