Shoe heel-toe drop affects running economy.

To run faster, distance runners need shoes that reduce their metabolic energy expenditure. Here, we studied how shoe heel-toe drop affects metabolic energy expenditure during running. To do so, we studied 20 runners as they ran at 3.5 m/s in custom footwear that varied in heel-toe drop: 0, 10, 20, and 30 mm. Shoe model and mass were fixed. Overall, increasing shoe heel-toe drop increased net metabolic power during running ([Formula: see text] = 0.12, P = 0.016); where changing from a 20 to 0 mm heel-toe drop reduced net metabolic power by 1.6%. Higher heel-toe drop decreased stance average vertical ground reaction force ([Formula: see text] = 0.10, P = 0.011) and increased average ankle effective mechanical advantage ([Formula: see text] = 0.28, P < 0.001). Higher heel-toe drop shoes increased average ankle plantarflexion angle ([Formula: see text] = 0.75, P < 0.001), leading to shorter medial gastrocnemius fascicle operating lengths at touch-down, toe-off, and on average during ground contact ([Formula: see text] ≤ 0.14, P ≤ 0.026). In addition, higher heel-toe drop increased peak and average knee moments during running ([Formula: see text] ≤ 0.40, P < 0.001). Therefore, longer triceps surae muscle fascicle operating lengths and reduced knee extensor moments likely contribute to more economical running in shoes with a lower heel-toe drop. Based on the metabolic and biomechanical findings, recreational and high-caliber distance runners who want to run faster should opt for shoes with a zero heel-toe drop.NEW & NOTEWORTHY By systematically varying shoe heel-toe drop between 0 and 30 mm, we discovered that a lower heel-toe drop elicits the best running economy. That is because a lower heel-toe drop enables medial gastrocnemius fascicles to operate at longer, more economical lengths, and it reduces knee extension moments versus higher heel-toe drop conditions. Thus, heel-toe drop can be considered in running shoes to further improve running economy.