Excessive shear stresses on the foot can cause a variety of problems. One of those problems is a condition called metatarsalgia. Metatarsalgia generally refers to pain in the metatarsal region of the foot, i.e., the area in front of the arch and behind your toes that includes the ball of your foot. The primary symptom is pain, especially during the mid-stance and propulsion phases of gait. Excessive calluses often form under the metatarsal heads.
Shear is an underappreciated cause of metatarsalgia. This article: McPoil TG, Schuit D, Management of Metatarsalgia Secondary to Biomechanical Disorders, Physical Therapy, 1986;66(6):970-72 (available for free) discusses how shear stresses are transmitted through the forefoot during gait. The presence of calluses under the metatarsal heads confirms that friction and shear are present at the forefoot. ShearBan® or ENGO® patches can be used to reduce the friction and lower the shear stresses. The locations of the calluses should guide you in deciding where to locate the patch of ENGO or ShearBan. For example, in the metatarsalgia case study by McPoil and Schuit, the callusing on the patient’s foot occurred under the second and third metatarsal heads (i.e., in the middle of the metatarsal region. ShearBan or ENGO should be placed on the insole of the shoe opposite this region of the metatarsal heads.