Isolated and combined effects of EVA and TPU custom foot orthoses on constant speed, treadmill running kinematics

Abstract

We investigated the isolated and combined (HYB) effects of ethyl-vinyl acetate (EVA) and expanded thermoplastic polyurethane (TPU) custom foot orthoses (CFO), compared to a control condition (CON; shoes only), on constant speed, treadmill running kinematics. Twenty (10 male) well-trained runners performed four, 6-min bouts at the same individualized speed for each bout on a treadmill under four footwear conditions (EVA, TPU, HYB and CON). Twenty markers and four clusters (four markers each) were placed on lower limbs and pelvis. Lower limbs and pelvis movements were tracked using a threedimensional motion capture system with 11 cameras (Vicon MX system, Oxford, UK). Lower limb joint angles and angular velocity were normalized to 100% of the stance phase. Peak ankle eversion (P < 0.001,  2 = 0.72), peak ankle eversion angular velocity (AV) (P < 0.001,  2 = 0.64), peak ankle inversion AV (P < 0.001,  2 = 0.60), and peak ankle internal rotation AV (P < 0.001,  2 = 0.49) demonstrated the largest differences between conditions. Statistical non-parametric mapping analysis revealed that HYB exhibited the largest proportions of change during the total stance phase compared to CON. All CFO materials caused significant reductions in peak angles and peak AVs at the ankle in the frontal plane, with more pronounced effects for harder (EVA) than softer (TPU) materials. These significant reductions occurred during large portions of the total stance phase for the angles and for AVs. While some effects could be found in more proximal joints such as knee and hip, most significant effects were found at the ankle joint. Overall, combining hard EVA material in the heel and soft TPU in the forefoot (HYB) resulted in significant, more favorable changes compared to CON, that lasted for the largest proportion of stance phase when compared to wearing shoes only.