Shear cushions reduce the impact loading rate during walking and running

In addition to vertical ground reaction force (GRF), anterior-posterior GRF with a greater external moment arm may be another repetitive impact force that contributes to overuse running injuries. In this study, a shear cushion device was placed between the sole of a shoe and the ground to reduce not only the vertical loading, but also the anterior-posterior loading while walking and running. For this study, 15 healthy male runners classified as heel strikers (height: 173.2 ± 4.7 cm, mass: 68.5 ± 5.6 kg) were recruited. Participants were required to walk (2.5 m/s), jog (3.5 m/s), and run (4.2 m/s) while wearing shoes with three different sole groove designs (conventional, straight groove, and 45° groove). Both the straight and 45° groove soles provided significant shear shift during walking, jogging, and running, as well as delayed the time to first peak anterior-posterior GRF during walking. The straight groove sole reduced the vertical loading rate during jogging (p = 0.010) and running (p = 0.010), and delayed the time to first peak vertical GRF in all gait conditions. These findings suggest that the vertical loading rate and the time to the first peak anterior-posterior GRF can be changed by the sole groove design under various gait conditions.