The effects of cycling shoe outsole material on plantar stress.

Past cycling-related literature noted that metatarsalgia and local paraesthesias are common among cyclists. The purpose of this investigation was to determine if shoes made with stiff material cause an increase in peak plantar stress over shoes with less stiff material. Plantar stress data were recorded in two different shoe types in an effort to form an association between cycling shoe stiffness and peak plantar stress experienced by cyclists’ feet. Two pairs of shoes of the same size and manufacturer, identical except for outsole material and stiffness, were tested. Shoe stiffness measurements were collected under controlled conditions and in two different configurations using a dynamic hydraulic tensile testing machine. The first test configuration occurred in a longitudinal bending arrangement as specified by ASTM standard F-911. The second shoe test arrangement was a custom three-point bending arrangement. It was anticipated that shoes made with carbon fiber materials would increase the peak stress experienced by the feet during normal cycling while more compliant shoes, made from other plastics, would reduce peak stress by exerting the stress over a greater area due to increased shoe deformation. Measurements of plantar stress were taken while subjects pedaled in a seated position at a controlled power output. Power output was set at a constant value of 400 W across all subjects by a magnetic resistance trainer unit that was thoroughly tested and calibrated for repeatability prior to use. Capacitive-based sensor insoles were placed in the shoes to measure the peak stress under each foot during pedaling. The stress distribution in carbon-fiber-composite shoes during cycling was compared to cycling shoes made with more traditional plastic soles. The shoes made with carbon fiber produced peak plantar stresses 18% higher than those of a more traditional plastic design (121.2 kPa vs. 103.0 kPa, p-value =0.005). Carbon fiber shoes presented stiffness values 42% and 550% higher than plastic shoes in longitudinal bending and three-point bending, respectively.