Background: Achilles tendinopathy is a common debilitating running related injury. Achilles tendon loading force has been hypothesized as a contributor to Achilles tendinopathy. Loading force through the Achilles tendon during running is impacted by many factors such as footwear and foot strike pattern. Achilles tendon biomechanical (Achilles tendon cross-sectional area, thickness, echogenicity, stiffness, and T2*) responses to loading forces are variable and measurable in vivo. These responses impact the physiologic function of the tendon. Aims: 1) To evaluate baseline Achilles tendon biomechanical characteristics associated with a runner's habitual foot strike pattern. 2) To evaluate single running bout Achilles tendon biomechanical changes to varied forces in runners while maintaining their habitual foot strike pattern. This will be accomplished using minimalist and cushioned running shoes. Methods: 29 recreational runners were recruited. Runners completed two separate 5.3 km running sessions wearing alternating shoe types (cushioned and minimalist) at a pace of 3.15 m/s. Prior to running each day, participants had 32 retroreflective markers placed upon them for motion analysis collection. Additionally, participants had their Achilles tendon imaged via ultrasound pre and post run. On a separate day 24 of the participants underwent an ultrashort echo time (UTE) MRI imaging session of their Achilles tendon. Results: Achilles tendon stiffness was 20% greater in non-rear foot strike runners when compared with rear foot strike runners (p = 0.0166). Achilles tendon CSA, thickness, echogenicity, and T2* were not different between running groups (p > 0.05). Both foot strike pattern groups experienced significant Achilles tendon CSA and thickness decreases from pre to post run in minimalist and cushioned shoes (p < 0.05). Both running groups in cushioned shoes and the non-heel strike runners in minimalist shoes experienced significant increases in Achilles tendon echogenicity from pre to post run. Only non-rear foot strike runners had a significant increase in Achilles tendon stiffness while running in cushioned shoes (p = 0.03). Conclusions: The Achilles tendons of non-rear foot strike runners were significantly stiffer than those of rear foot strike runners. This Achilles tendon characteristic may be attributable to differences in Achilles tendon loading force while running but needs further research. Both groups of runners experienced multiple single running bout Achilles tendon changes as measured via ultrasound. Although loading forces varied within groups in different shoes and between foot strike pattern groups, all Achilles tendon changes were similar regardless of loading forces from pre to post run.