Running Shoe With Extra Midsole Thickness Increase Foot Horizontal Instability During Treadmill Running

Purpose: Opposite to the design concept of the minimum running shoes, maximum running shoe provides extra midsole thickness for additional cushioning. This additional midsole thickness might lead to instability in both medial-lateral (ML) and anterior-posterior (AP) directions. The goal of this study was to compare peak forces and the variability of forces (FVar) in horizontal directions (ML and AP) among maximum, regular, and minimum running shoes. Methods: Eight participants ran on instrumented treadmill at 3.5m/s wearing three different running shoes in a random order. In each trail, ten steps were recorded bilaterally for both left and right. Maximum force (FMax) and Minimum force (FMin) were calculated for each step at the ML and AP directions. Variability (FVar) was calculated with the standard deviation of the ten-trial ensemble curve at every ten percent of the stance phase. Three-way MANOVA (Shoe, each ten percent section and L/R foot as independent variables) was performed to detect the different variability of forces (FVar-ML and FVar-AP) among three running shoes at horizontal directions. Two-way MANOVA (Shoe and left/right foot as independent variables) were performed to determine the different peak forces at ML and AP directions (FMin-ML, FMax-ML, FMin-AP, and FMax-AP). Tukey post hoc employed when needed. Alpha was set at .05. Results: Significant different peak forces were observed among different running shoes in the positive directions (anterior and lateral). FMax-ML (lateral) for the regular shoe (89.7±3.1 N) was much greater than that of the minimum shoe (76.3±3.1 N) and the maximum shoe (75.2±3.1 N). Positive AP (anterior), FMax-AP for the maximum shoe (229.1±3.8 N) was much greater than that of the minimum shoe (213.2±3.8 N). There was significant different variability among three types of shoes. FVar-AP showed significant difference, where FVar-AP for the maximum shoe (39.4±1.1 N) was much greater than that of the minimum shoe (35.3±1.1 N). Conclusions: Comparing to regular and minimum running shoes, maximum shoe provides greater horizontal instability, specifically greater medial-lateral peak force and greater variability at the AP direction