Increased step width has been described as a technique to reduce instability in the lateral plane during walking. Humans have been shown to exploit the trade-off between step width and stability in response to internal factors such as cognitive demands. External factors, such as carrying loads and negotiating a cluttered environment also alter stability. PURPOSE: To determine if carrying loads and negotiating an elevated surface resulted in increased step width. METHODS: Ten young males (25.4 +/- 3.6 yrs) walked along a 10 m walkway. Gait mode conditions included (1) level walking and (2) negotiating a raised surface (0.15 m high, 1 m wide, 3.7 m long). Load handling conditions included: (1) no load, (2) an empty box (negligible mass) and (3) the same box loaded with the equivalent of 5% body mass. Infra-red emitting diodes were placed bilaterally on the toe and heel and recorded with Optotrak (NDI). RESULTS: The step width was dependent on both the gait mode and the load (gait * load, p = 0.004). During level gait, the step width increased from 10.5 to 10.6 to 10.7 cm for no load, empty box and weighted box. Step width further increased when negotiating the surface with either no box (10.9 cm) or the empty box (11.0 cm). However, during the most challenging task, surface and load, the step width was the smallest (10.4 cm). CONCLUSION: The stability challenge of the load or surface, presented separately, resulted in increased step width as expected. However, the step width decreased when the two were presented together. In this condition, the increased trunk angle due to stepping up, combined with the increased inertia, may lead to an unstable trunk, and widening the step appears critical. However, the increased step width may result in even greater trunk displacement, further compounding the challenge. It appears that when stability was challenged by both the surface and the load, increased step width was not a viable strategy.
Department of Environmental Health, University of Cincinnati, Cincinnati, Ohio