The Effects of the VK Performance Insole on Running Economy in Highly-Trained Distance Runners

Abstract

Several design features of running shoes such as decreased mass, appropriate midsole cushioning, and increased longitudinal bending stiffness are associated with improved running economy (RE). While increased longitudinal bending stiffness has been achieved through the use of carbon fiber plates inserted into shoe midsoles, there are several limitations associated with this construction method. An alternative solution to increase longitudinal bending stiffness in running shoes is to utilize a carbon fiber shoe insole (CFI) tuned for optimal mechanical efficiency of the athlete-footwear system. PURPOSE: To determine if a carbon fiber shoe insole (VK Performance Insole; VKTRY Gear; Milford, CT) can improve running economy in highly-trained distance runners. METHODS: Ten highly-trained male distance runners (age: 24.7 ± 6.8 years, height: 177.9 ± 5.59 cm, mass: 67.7 ± 5.7 kg) participated in this study. To measure RE, participants ran for 6 min at 16 km·hr-1 for the following three conditions: 1) control footwear (no CFI), medium flex CFI (VK Pro 4), and 3) stiff flex CFI (VK Pro 5). Indirect calorimetry was used to measure oxygen consumption (VO2). The first 4 min were to allow the athlete to reach a steady state and metabolic data from the last 2 min were used to determine submaximal VO2. The shoe insole conditions were presented in random order; each RE test was separated by a period of 6 min to minimize the effects of fatigue. A repeated-measures ANOVA was used to determine the effects of shoe insole condition on RE. RESULTS: The submaximal VO values for each of the shoe insole conditions were as follows: 1) control (no CFI): 49.8 ± 3.0 ml·kg-1·min-1; 2) medium flex CFI (VK Pro 4): 50.2 ± 3.5 ml·kg-1·min-1; and, 3) stiff flex CFI (VK Pro 5): 51.3 ± 3.1 ml·kg-1·min-1. Based on these submaximal VO values, there was no difference in RE between the three different shoe insole conditions [F(2,8) = 0.97, p = 0.44]. CONCLUSIONS: Previous studies have shown that increased longitudinal bending stiffness achieved through the use of carbon fiber plates inserted into shoe midsoles can significantly improve RE by 1-4%. However, the use of a CFI did not result in similar improvements in RE. Further design work and testing of the CFI is required to determine the optimal longitudinal bending stiffness for improved RE at submaximal velocities.