A sole assembly which includes a heel cradle configured to cradle a heel of a human foot when the human foot is rested within the heel cradle  a rigid upper plate including a first part connected to the heel cradle and a second part located farther from the heel cradle than is the first part  a lower plate including a first part of which is connected to the first part of the upper plate and including a second part which is connected to the second part of the upper plate  an oblong gap located between the upper plate and lower plate and between the first and second parts of the upper and lower plates