The shifting of the torsion axis of the foot during the stance phase of lateral cutting movements.

Previously, foot torsion has been studied with respect to peak angles during athletic movements. Athletic footwear often contains a torsion element that dictates a torsion axis of the shoe. The location of the axis of rotation of the foot is, however, unknown. Therefore, the purpose of this study was to describe the torsion axis location during the stance phase of lateral cutting movements. Thirty-nine subjects performed a barefoot lateral jab and 19 subjects performed a barefoot shuffle cut. Markers were placed on the fore- and rearfoot and their movement was quantified using a 3-D video system. The torsion axis location was determined using a modified finite helical axis approach during the stance phase while the torsion angle was calculated as the amount of rotation around the torsion axis. At the beginning of the stance phase, the axis was located on the medial aspect of the foot. During the stance phase, the axis shifted towards the lateral side of the foot before the axis moved back to the medial aspect of the foot at the end of stance. For both movements significant correlations between the axis location in the vertical and medio-lateral directions and the torsion angle were found. With larger torsion (forefoot inversion) angles the axis was in a more lateral and plantar location within the foot. With this knowledge, a shoe torsion system where the shoe torsion axis location is in agreement with the foot axis location could be developed.