Hahn, MichaelFarina, Kathryn2022-05-102022-05-102022-05-10https://hdl.handle.net/1794/27143Achilles tendon injuries are one of the most common running related injuries. Injuries to the Achilles tendon are painful, often involve long recovery and rehabilitation, and many patients are non-responsive to current treatments. One hypothesis for development of injury involves the combined action of frontal plane rearfoot motion and tibial rotation during the stance phase of running, leading to damage, and possible injury, within the tendon tissue if not given adequate time to recover. Targeting these actions of rearfoot motion may alter stress in the tendon, possibly decreasing injury risk, or providing alternate avenues of rehabilitation by addressing underlying movement patterns. The purpose of this dissertation was to evaluate how increasing step rate during running affects motion at the rearfoot and how changes in rearfoot motion affect stress in the Achilles tendon in healthy and injured runners. This dissertation was divided into three projects. Project 1 involved twenty healthy runners running with +5% and +10% increases in step rate on a force-instrumented treadmill, while motion capture data were collected. Results indicated increasing step rate significantly reduced peak rearfoot angles in the sagittal and frontal plane and reduced tibial internal rotation in the transverse plane. Project 2 used these previously collected data in a generic calcaneus and Achilles tendon finite element model to estimate changes in Achilles tendon stress as a result of increasing step rate. Conflicting results were observed, as the finite element model produced increased stress in the Achilles tendon with increased step rate but calculating stress with cross sectional area showed decreases in stress. Project 3 repeated procedures from Projects 1 and 2; however, runners with Achilles tendon injury were recruited for this final study, with magnetic resonance imaging scans of their injured leg used to create subject-specific finite element models. The results showed no significant differences in Achilles tendon stress with increased step rate, however results were variable between subjects. The results of this dissertation indicate increasing step rate significantly affects rearfoot motion; however, constraints in the finite element models and high subject variability led to inconclusive results concerning how increasing step rate affects Achilles tendon stress.en-USAll Rights Reserved.Achilles tendongait retrainingrunningstep ratetendinopathyElectronic Thesis or Dissertation