Effects of a 12-week gait retraining program on the Achilles tendon adaptation of habitually shod runners

This study investigated the effects of a 12-week gait retraining program on the morphological and mechanical properties of the Achilles tendon (AT) during running on the basis of real-time dynamic ultrasound imaging.

A total of 30 male recreational runners who were used to wearing cushioned shoes with a rearfoot strike (RFS) pattern were recruited. They were randomized into a retraining group (RG, n = 15) and a control group (CG, n = 15). The RG group was asked to run in five-fingered minimalist shoes with a forefoot strike (FFS) pattern, and the CG group was asked to keep their strike pattern. Three training sessions were performed per week. All the participants in RG uploaded running tracks obtained through a mobile application (.jpg) after each session for training supervision. The ground reaction force, kinematics, and kinetics of the ankle joint at 10 km/h were collected using an instrumented split-belt treadmill and a motion capture system. The morphological (length and cross-sectional area) and mechanical characteristics (force, stress, strain, etc.) of AT in vivo were recorded and calculated with a synchronous ultrasonic imaging instrument before and after the intervention. Repeated two-way ANOVA was used to compare the aforementioned parameters.

A total of 28 participants completed the training. The strike angle of RG after training was significantly smaller than that before training and significantly smaller than that of CG after training (F _{(1, 13)}  = 23.068, p < 0.001, partial η²  = 0.640). The length (F _{(1, 13)}  = 10.086, p = 0.007, partial η²  = 0.437) and CSA (F _{(1, 13)}  = 7.475, p = 0.017, partial η²  = 0.365) of AT in RG increased after training. A significant main effect for time was observed for the time-to-peak AT force (F _{(1, 13)}  = 5.225, p = 0.040, partial η²  = 0.287), average (F _{(1, 13)}  = 7.228, p = 0.019, partial η²  = 0.357), and peak AT loading rate (F _{(1, 13)}  = 11.687, p = 0.005, partial η²  = 0.473).

Preliminary evidence indicated that a 12-week gait retraining program could exert a beneficial effect on AT. 57% (8/14) runners in RG shifted from RFS to FFS pattern. Although not all runners were categorized as FFS pattern after the intervention, their foot strike angle was reduced. Retraining primarily positively promoted AT morphological properties (i.e., CSA and length) to strengthen AT capability for mechanical loading.