Lower-limb muscle activity when walking on different slippery surfaces

Falls initiated by slipping are a major cause for concern for lower-limb amputees, due to their lacking the distal musculature that aids in avoiding the initiation of a slip. It has been previously demonstrated that able-bodied individuals can interact safely with slippery surfaces by adapting limb kinematics and altering muscle activity to minimize slipping. Newly developed prosthetic devices have the potential to restore specific gait modes to the user, such as walking on a slippery surface, if only more was known about how the mechanical properties should be regulated in each mode. As a first step towards understanding the mechanics relevant to slip prevention, this study sought to quantify lower-limb muscle activity during steady state walking on a range of slippery surfaces. A specific goal was to quantify how people walk on moderately slippery surfaces that pose a hazard, but are more likely to be found on an everyday basis than some of the surfaces previously studied. Our results showed a significant trend (p<0.001) towards decreasing the level of activity used at the ankle as the floor becomes more slippery. In contrast, there is a significant trend (p<0.001) towards increasing the level of activity used at the knee. These findings suggest a strategy in which the ankle becomes increasingly compliant to maximize the surface area in contact with the floor, while increased activity in proximal muscles is used to help stabilize the legs and trunk for increased safety.