Objective To investigate the mechanical properties of Achilles tendon (AT) during running under different shoe conditions (minimalist vs conventional shoes). MethodsSixteen healthy male runners with habitual rearfoot strike patterns were recruited to complete the running trials at the speed of 3.16~3.50 m/s under two shoe conditions. The cross-sectional area of the AT was obtained by ultrasound imaging. Sagittal plane ankle kinematics and ground reaction forces were recorded by motion capture system and three-dimensional force platform simultaneously. Mechanical properties of the ankle and AT were calculated. Paired t test was used to compare the effects of two shoe conditions on various parameters (ankle angle, strike angle, AT force, stress, strain, etc). ResultsCompared with conventional shoes, foot inclination angle was significantly reduced by 39.9% with minimalist shoes. Obvious increase in ankle moment, peak AT force, peak AT loading rate, average loading rate, and obvious decrease in time to peak AT force were observed with minimalist shoes. Peak AT stress, peak AT strain and corresponding stress rate, peak strain rate also increased significantly with minimalist shoes. ConclusionsGreater AT loading was observed when runners with habitual rearfoot strike pattern in conventional shoes begin to wear minimalist shoes. Therefore, a gradual transition to minimalist shoes was recommended for them so as to improve the ability to load adaptively.