With every step, your body absorbs force that can lead to overuse injuries in the Achilles tendons, heels, and ankles and pain in the knees, hips, and lower back, says Rock Positano, director and founder of the Joe DiMaggio Heel Pain Center and the Non-surgical Foot and Ankle Service at the Hospital for Special Surgery in New York City. An intact heel counter (the very back of your shoe that cradles your Achilles) absorbs some of that shock, protecting you from those issues.
“Slipping your sneakers off instead of untying the laces puts undue stress and strain on the heel counter, causing deformation and breakdown of the shoe’s material,” Positano explains. The habit also stretches this part of the shoe, compromising fit and comfort.
The bottom line:
You can make your running shoes last 10 to 15 percent longer by untying them before taking them off. Once you've logged 300 miles in them or the treads wear down—or worse, you feel pain in your heels, knees, or lower back while running—you’re due for a new pair, Positano says.