All current running shoes, including "minimalist" ones, do not allow localized plantar deformations and shear stress - adequate stimuli of SA II mechanoreceptors and nociceptors with c-fibre afferents. This plantar tactile information is required to elicit behavior that moderates impact, achieves optimal stability and protects the plantar surface when barefoot. Despite this, impact might not be excessive so long as balance was optimal, since instability elicits behavior that amplifies impact. With low tactile information, humans can maintain suboptimal but adequate stable equilibrium though muscle receptor sensing of position and orientation of the foot. Unfortunately, all athletic footwear, and most non-athletic footwear are made with materials that strongly destabilize humans because they incorporate high resiliency sole material. High resiliency is the property of rapid rebound after deformation from compressive load - some manufacturers ironically advertise this as a desirable property of "energy return." This material underfoot transforms the normal highly damped state of the bare foot to an underdamped one consisting of rapid medial-lateral and vertical oscillation, surpassing the muscle receptors ability to provide reliable information about foot position and orientation. This results in both a sense of instability and actual increase risk of falling. Instability elicits an intense behavioral response that includes amplified impact which appears to be an innate reaction to prevent falling through seeking a firm support base. The instability elicited by these materials is a negative function of their thickness and positive function of hardness. Even relatively thin layers of high resiliency material of hardness usually found in shoes is capable of destabilizing humans considerably.