Objective To investigate the acute effect of changing foot strike patterns on in vivo kinematics of the medial longitudinal arch during shod running. Methods The high-speed dual fluoroscopic imaging system(DFIS) was used to acquire fluoroscopic images of the right foot during stance phase before and after changing foot strike patterns [running speed: (3±0. 15) m / s] in 15 healthy male runners. The three-dimensional (3D) model of the first metatarsal bone and calcaneus and the local coordinate system were reconstructed from CT images, and the six degrees of freedom (6 DOF) data of the medial longitudinal arch (simplified as motion of the first metatarsal bone relative to the calcaneus) during stance phase were obtained by 3D-2D registration. Statistical parametric mapping (SPM) was used to compare the 6 DOF data of the medial longitudinal arch before and after changing foot strike patterns, and paired sample t-tests were used to compare the specific values. Results Compared with rearfoot strike, the lateral translation during 15% -21% of stance phase, anterior translation during 17% -45% of stance phase and dorsiflexion during 18% -39% of stance phase for motion of the first metatarsal bone relative to the calcaneus were significantly increased during forefoot strike running ( P < 0. 05). The maximum anterior translation, the maximum dorsiflexion, the anterior-posterior translation, and the compression of the medial longitudinal arch for motion of the first metatarsal bone relative to the calcaneus were significantly increased during forefoot strike running (P<0. 05). Conclusions Transitioning from habitual rearfoot strike to immediate forefoot strike resulted in greater deformation of the medial longitudinal arch in sagittal plane, especially the variation of arch compression increased by approximately 10% , which might contribute to the storage and release of elastic energy in the medial longitudinal arch.