Ultrasound-Based Mechanical Adaptation of Achilles Tendon After 12-Week Running with Minimalist Shoes

This study aimed to investigate the effect of a 12-week running program using minimalist shoes on ultrasoundbased mechanical adaptation of Achilles tendon (AT). Fifteen male recreational runners accustomed to run in standard cushioned shoes with rearfoot strike pattern were recruited. They were required to wear minimalist shoes without a compulsory transition in foot strike pattern, and be involved in a 12-week running program. Before and after the intervention, the cross-sectional area of AT was collected in the prone position via an ultrasound device. The ankle plantarflexion moment, recorded on an isokinetic dynamometer, was synchronized to the image changes in vivo AT length. Intraclass correlation coefficient was determined to evaluate the intraand interobserver variabilities. Paired t -test was used to quantify the effects of training program (pre- and posttraining) on each variable of the cross-sectional area, AT force, AT stress, and AT strain during an isometric contraction. Seven participants dropped out after the intervention. The results showed that the intraclass correlation coefficients for the intra- and interobserver reliabilities were good to excellent (intraclass correlation coefficients = 0.895–0.996) for the cross-sectional area and elongation. After 12-week running with minimalist shoes, plantarflexion moment, AT force, AT stress, and AT strain significantly increased during an isometric contraction ( P < 0.05). The mechanical adaptation of AT improved after 12-week running with minimalist shoes by more efficient energy storage and release, which could prevent or reduce the risk of injury potentially.