The Interaction Of Treadmill Surface Stiffness And Footwear Cushioning On Running Energetics And Biomechanics

Increased surface compliance and increased shoe cushioning can both improve running economy to a certain point, after which a damping effect can occur to worsen economy. The interaction effect of these two variables during treadmill running has yet to be thoroughly investigated. Increased leg stiffness may provide a mechanistic explanation for improved economy, though previous findings have varied. PURPOSE: To compare running economy and mechanics in shoes with more or less cushion while running on a rigid or compliant treadmill. METHODS: 12 runners completed four 5-minute bouts at a self-selected submaximal pace (8:03 ± 0:43 min/mile) in shoes with more (34 mm thickness) or less (28 mm thickness) cushion (same foam) on rigid (Bertec force instrumented) and compliant (RUN Excite, Technogym) treadmills in a randomized order with a 3-minute rest period between bouts. Expired gases, kinematics, and ground reaction force data were collected during each bout. A two-way repeated measures ANOVA was used to compare RE (volume of oxygen consumption; VO2) as well as knee flexion excursion, vertical pelvis oscillation, peak in-shoe vertical reaction force, and vertical stiffness during the stance phase of running. Paired t-tests with Bonferroni corrections were used to compare means and Cohen's d effect sizes were computed. RESULTS: No interaction effects were observed for any of the dependent variables. Shoe mass corrected VO2 was 2% higher in shoes with more compared to less cushion (p < 0.001, d = 0.41). Knee flexion excursion was greater on the rigid compared to compliant treadmill (p < 0.001, d = 1.03) but treadmill stiffness did not affect economy. CONCLUSION: Shoes with more cushioning may moderately worsen running economy but two different treadmill (and possibly surface) stiffnesses does not appear to influence this effect. The mechanism for this shoe cushioning difference in economy is unclear.