31 at that certain length during expansion of the unit 31 unit 31 expanded and recovered its original shape more slowly than it was compressed the fc fr ratio was not one or nearly one but was greater than 1 typically at least about 1 10 for compressive forces in the range of fifty to about 300 pounds per square inch an elastomer which when a cylindrical unit 31 of the elastomer is tested which has a diameter of 0 69 and length of six inches has an fc fr ratio in excess of 1 10 for compressive and rebound forces in the range of fifty to three hundred pounds per square inch is preferred in the practice of the invention and makes the leg prosthesis of the invention unusually comfortable an fc fr ratio equal to one is not acceptable in the practice of the invention because this simulates a spring which expands as rapidly as it compresses when an elastomer linearly expands at a rate which is as rapid as the rate at which it is linearly compressed the comfort afforded by the apparatus of the invention is adversely impacted the fc fr ratio cannot be too great otherwise the elastomer unit 31 will not rebound quickly enough or will not substantially return to its original length when it rebounds consequently when an elastomer unit 31 which is 0 69 inches in diameter is six inches long and is subjected to a force of three hundred pounds and is allowed to rebound the average fc fr for compression fc and rebound fr forces in the range of fifty to 300 pounds per square inch is in the range of 1 10.