THE EFFECT OF FOOTWEAR MIDSOLE HARDNESS AND THICKNESS ON PROPRIOCEPTION AND STABILITY IN OLDER MEN

Support surface interface (footwear, flooring systems, etc), thickness , and hardness strongly influence stability in men of all ages. We hyp othesize interfaces influence stability through their effect on propri oception. We tested this by means of an experiment based on a randomiz ed, cross-over, and controlled comparison design. Footwear midsole har dness and thickness were independent variables. Dependent variables we re foot position and perception of foot position, measured concurrentl y. Thirteen subjects were a random sample of healthy older men (mean a ge 72 years, sd +/- 4.50). They were tested barefoot using six support surface interfaces consisting of shoes that were identical, except fo r midsole hardness and thickness, that spanned the respective ranges i n current footwear. Measures were balance failure frequency defined as falls per 100 m of beam walking, rearfoot angle measured via an optic al position measurement system, perceived maximum supination estimated by subjects via a ratio scale when walking, and foot position error, defined as rearfoot angle minus perceived maximum supination. The resu lts demonstrated: (1) foot position awareness was positively related t o stability; (2) foot position error was negatively related to support surface interface thickness; (3) foot position error was positively r elated to support surface interface hardness; and (4) foot position er ror correlated best with maximum supination. We conclude that instabil ity induced by support surface interfaces is caused by its effect on f oot position awareness. Thin hard-soled shoes provide superior stabili ty for older men. Most currently available footwear provides poor stab ility because soles are too soft and thick. Since suboptimal support s urface interfaces are encountered by everyone daily, they represent su bstantial safety hazards. Likewise, improving this situation through s etting stability safety standards is a promising means of improving pu blic safety. At the very least, the public must be informed about prod ucts imparting suboptimal stability so that they can anticipate potent ial problems and compensate for them without falling.