Torsion of the foot reduces the coupling between forefoot and rearfoot motion in the frontal plane. While the amount of torsion occurring in running and cutting has previously been described, the exact location of the rotation axis has not been detennined. It is known that footwear restricts torsional movement;​ it is unknown what effect footwear torsional stiffoess has on lower extremity joint biomechanics. Therefore, the purposes of this thesis were to 1) develop and assess the repeatability of a method to calculate the location of the torsion axis, 2) describe the torsion axis location during cutting movements, 3) determine the influence of footwear torsional stiffness on torsion angles and lower extremity joint biomechanics during running and cutting movements, and 4) quantify the effect of footwear torsional stiffness on perfom1ance during cutting movements.

The torsion axis location was calculated usmg a modified finite helical axis approach, which allowed the calculation of the rotation axis between the forefoot and the rearfoot without the influence of forefoot flexion. The repeatability assessment of the modified finite helical axis approach revealed that the torsion axis location can be calculated repeatable for movements with large torsion angles. For movements with small torsion, however, it cannot be quantified due to the susceptibility of the method for error with small rotations.

During the stance phase of cutting movements the torsion axis shifted from an initially medial location within the foot to a lateral location during mid-stance when the torsion angle was large. Towards the end of stance, the axis moved back to the medial side of the foot. The average axis calculated over the entire stance phase was located on the lateral aspect of the midfoot.

When wearing torsional stiff shoes, the peak torsion angle was reduced for running, a lateral jab and a shuffle cut when compared to a flexible shoe. Even with a flexible shoe, the peak torsion was reduced compared to barefoot. Stiff shoes led to increased peak ankle inversion angles and peak eversion moments for the shuffle cut. No differences in performance during lateral cutting movements were found between footwear with different torsional stiffness.