Yeah, you could run in those cute walking shoes or older-than-dirt trainers, but please don’t. “When you run, you hit the ground with force greater than two times your own body weight,” says Jeff Dengate, shoes and gear editor at Runner’s World. “Running shoes are built with higher-quality, lightweight materials that help lessen that impact.”  While a good pair can easily set you back $100-plus, making the investment now could save you a boatload later in potential doctors and PT bills. and be sure your new pair meets the following criteria:

  1. Has enough toe length Feet swell when you run, so aim for a thumbnail-length of space between your longest toe and the end of the shoe. Don’t be surprised if you wind up in a ½- or full size larger than your street shoes. 
  2. Has enough toe width Squished-in toes equal blisters. Make sure there’s some wiggle room in the toe box.
  3. Skips seams Look for a seamless upper (seams can rub, causing blisters) that comfortably hugs the top of your foot.
  4. Has the right arch The arch should contour to the shape of your foot. You may need to add an insert for a more customized fit. 
  5. Holds your heel Make sure your heel stays in place before buying. Find out with a quick jog around the store (or on the treadmill if they have one). 
  6. Feels firm Pillowy cushion feels nice, but a firmer shoe is best if you’re coming back from an overuse or impact injury; it’ll have more spring-back on the road, minimizing stress on stabilizing muscles. 
  7. Flexes right Check the shoe’s flex point (where it creases when you press the toe into the floor). It should bend at the same place as your foot to ensure a natural stride. MORE: How Running Crushes YourHeart AttackRisk—No Matter How Slow You Go