When should you replace your running shoes?

What happens to a shoe as you run

Most of the life of a running shoe is in the midsole foam. With every step it compresses and springs back. Over hundreds of kilometres, the foam slowly loses some of that ability: it gets firmer and cushions less. The outsole rubber wears away, and the upper can stretch or tear.

What the studies found

• In a 2017 study, experienced recreational runners who land on their heels ran in new shoes while researchers measured the midsole regularly. After 480 km, the heel cushioning was reduced by 16–33%. The striking part: the runners didn't notice. Even after 640 km, they didn't report a meaningful change in how cushioned the shoes felt.
• A 2010 study with 15 amateur runners measured shoes every 50 km up to 500 km and found a smaller change: about a 5% increase in peak impact force. The authors noted that machine tests, which simulate running in a lab, tend to overestimate how fast cushioning breaks down compared with real running.

Two lessons follow. First, shoes do lose cushioning over a few hundred kilometres. Second, you can't rely on feel alone to know when that has happened.

And injuries?

This is where the evidence gets thin. There's no strong research showing that running in shoes past a certain kilometre count causes injuries. Training load – how much and how quickly you increase it – is a much better-supported risk factor. So replacing shoes is sensible maintenance, not a magic shield.

A practical approach

1. Track your kilometres. Most running apps and watches can log distance per shoe. Otherwise, write the start date inside the tongue.
2. Start paying attention around 500 km. Lighter racing shoes with soft foams often wear faster; durable daily trainers often last longer.
3. Look for real signs of wear:
   • the midsole has deep creases or feels flat and hard,
   • the outsole is worn through to the foam in places,
   • the heel counter has collapsed or the shoe leans to one side on a table,
   • the upper is torn or no longer holds your foot.
4. Notice new aches that appear after runs in that pair but not in others.
5. Consider two pairs in rotation if you run often. It spreads the wear and lets you compare a fresh pair with an old one – which makes worn-out shoes much easier to spot.

Things that shorten a shoe's life

• Higher body weight and a strong heel strike
• Lots of road running compared with soft paths
• Using running shoes for everyday walking, gym work or standing at work
• Drying them on a heater, which can damage foam and glue