A typical slip and fall event during normal ambulation occurs when the heel of the forward/swing leg contacts the floor and the foot slides forward against the floor surface due to an inadequate level of available friction. As the leading foot moves forward, the body’s center of mass (i.e. torso) moves in a rearward direction towards its boundary of stability. If balance recovery strategies, including reflexive arm responses and the placement of the non-sliding foot behind the slipping foot, are not successful, a rearward fall will occur.
Normal ambulation entails that the foot entering swing phase be lifted off the ground and progressed forward as part of the human gait cycle. A tripping mechanism occurs when the foot, during swing phase, interacts with an obstacle or some structure of the surface that protrudes above the walking surface. The obstacle must not only have sufficient dimensional attributes to cause a perturbation during ambulation and be within the expected path of pedestrian traffic, but it must be inherently unexpected. A trip and fall occurs when the body’s lower extremities’ forward progress is impeded, causing the body’s center of mass to unexpectedly move forward beyond its base of support to an extent that it compromises the body’s dynamic equilibrium. If balance recovery strategies are not successful, including reflexive arm responses and the repositioning of the stance leg such that the new location is ahead of the tripped foot, a forward fall will occur.