  The biomechanical studies have proposed several forward fall arresting
strategies to reduce the impact forces in a human-robot collaboration
environment. A proposed strategy is using a compliant flooring for an
environment because it can reduce the stiffness of the ground. In this study,
we proposed that if a rigid layer is mounted on a compliant flooring
(double-layer flooring), the impact force is further reduced. In order to
investigate this goal, we designed two subjective laboratory experiments. In
experiment 1, the subjects were instructed falling to the ground where was
covered by a single layer of compliant material (a foam pad). In experiment 2,
the subjects fell on double-layer flooring when one rigid layer (a wood
surface) was mounted on the compliant layer. The impact forces were measured
for two short forward fall heights onto the outstretched hand. The results
showed that the profile of the impact forces consists of two peaks. The first
peak has a higher magnitude, and it is followed by the second peak with a lower
magnitude. Comparing the magnitude of the first peak between two experiments
shows a reduction of the impact force in experiment 2. In contrast, the
magnitudes of second peaks are identical for both experiments. Therefore, we
concluded that using a double-layer flooring, i.e.one rigid layer and one
compliant layer can be an effective strategy for considerably reducing the
impact force, and preventing the wrist fractures during the forward fall.
