You probably shouldn't worry about it. Here’s why:
Cushioned running shoes get their bounce from midsoles typically made with EVA, a type of foam that loses air with repeated use, reducing its cushioning capabilities.
Treadmills, on the other hand, have cushioning systems located beneath the belt and the deck—the part of the treadmill the belt slides over—that help absorb shock. Some manufacturers use springs to create that cushioning, but most use a durable rubber, much like the rubber used in car bumpers.
We checked in with Greg Law, director of engineering for Icon Health and Fitness, the company behind popular treadmill brands FreeMotion, NordicTrack, and ProForm. “That cushioning system will last for the life of the product unless there's some sort of manufacturing defect,” says Law. The normal lifespan of a treadmill is 10 to 15 years, after which owners usually trade up.
And there are good reasons to upgrade. Construction of the cushioning system varies between manufacturers and has improved over time. Most modern treadmills have variable cushioning, meaning there’s more shock absorption toward the front of the machine, where the foot strikes, than in the back, where the foot pushes off. Exercise equipment manufacturer Proform claims that their latest treadmill cushioning system reduces impact by up to 33 percent, compared to running on the road.