Here’s how often you really need to replace your running shoes
Google ‘When do I need to replace my running shoes?’ and the internet’s collective ‘wisdom’ advises somewhere between 300-500 miles. But dig deeper and you’ll find scant scientific evidence behind this decades-old rule-of-thumb. Add our increasing awareness that the more miles we run in our shoes, the lighter we tread on the planet, and elite runners like Jasmin Paris being vocal about pushing shoes past 1,000 miles, and the blunt 300-500 mile yardstick looks increasingly outdated.
However, many manufacturers still use a version of it, often based on their own unpublished durability tests. It’s easy to accuse shoemakers of promoting these upper lifespan limits in some nefarious shoe-selling plot. But then you’ll often hear physios, coaches and running experts sharing the same advice.
What’s certain is rapid advances in shoe technology have transformed our running shoes and that raises new questions. Do modern foams last longer? Do shoes still have a set lifespan? Or can we run in them until they literally disintegrate without risking injury?
Unpacking the '300-500 miles' rule
Let’s go back to that stubbornly enduring ‘rule’. It appears to come from one 1985 study, in which researchers used a combination of machines and humans to investigate shock absorption in a range of running shoes from zero to 500 miles.
The shoes retained around 80% of shock absorption after 150 miles. That dropped to 70% at 500 miles. However, between 300 and 500 miles, the curve flattens and the loss of shock absorption bottoms out. If impact protection is your top priority – and you’ve run past 300 miles without any major issues – there’s arguably no compelling reason in the research to ditch your shoes. But crucially, that research is from 1985 when shoes – and our expectations – were different.
In recent years, we’ve swapped thin wedges of hard, heavy EVA for soft, light and bouncy nitrogen-infused superfoams. We’ve added carbon and nylon plates, featherweight mesh uppers and plant-based components. Running shoes are now fine-tuned to deliver precise benefits for every different type of run. A stripped-back, carbon racer built for speed is a very different proposition to a max-stack daily trainer made for long-haul comfort.
Designers select different materials to fulfil these specific priorities and this precision of purpose has repercussions for the longevity of our shoes. Even if the one-size fits all mileage quota once had value, in the era of superfoams and super-specific super shoes, it now seems far less likely to work.
A new era of midsole
Our expectations mirror this design evolution and we now expect shoes to do much more than simply reduce impact. Beyond comfort and protection, we want energy return and responsiveness to deliver running economy and performance gains. We want shoes that help keep legs fresh the day after hard sessions. And to deliver all this, midsoles have taken a giant leap forward.
The most common foams now roughly break down into two camps: standard foams like EVA (HOKA Profly+), TPE (Altra Ego Pro) and TPU (Adidas Boost/Saucony PWRRUN+) and premium foams like PEBA (Asics Flytefoam Blast Turbo), PEBAX (Nike ZoomX) and TPEE (Adidas Lightstrike Pro).
The ‘standard’ foams tend to be cheaper, more durable and more stable but offer lower energy return. Premium foams offer big energy returns but may possibly compromise on durability – or at least the durability of their performance benefits. These aren’t always the same thing. But more on that in a moment.
Then there are supercritical foams created using supercritical fluid – often nitrogen – as a blowing agent, to expand foams, essentially creating bubbles throughout. This process gives manufacturers precise control over properties like compliance, resilience and density. The result is foams with enhanced performance characteristics such as improved cushioning and energy return, but they can be less hard wearing.
Just to make things even more complicated, to unlock the best of both worlds, brands increasingly use foam blends. For example, Nike’s React foam is a mix of TPE and EVA with the EVA adding durability.
Performance endurance
The lifespan of these new midsole materials is now judged not only by how long it delivers protective cushioning but also whether it continues to boost energy and efficiency. Thankfully, the performance and durability of foams has generally improved. Though not all foams tick both boxes — peak performance isn’t always long-lasting.
‘Generally foams have taken big leaps over the past few years for all brands,’ says Rohan Van der Zwet, Senior Product Marketing Manager at Asics. ‘This is why we have much higher stack heights and midsoles because the foams are lighter, more durable and return more energy.’
Andy Farnworth, co-founder of sustainable running shoe brand Zen Running Club, works with major foam suppliers to all the big brands. He’s seen the improvements first hand, even in plant-based and premium supercritical foams. ‘We’ve tested quite an advanced compression-moulded EVA and we were seeing next to nothing in the decrease in cushioning performance over 500km (310 miles),’ says Farnham. ‘I think up to 500km, you can pretty much say it's still good. And that's any foam. The supercritical foams are slightly less durable but not much.’
However, not all foams are created equal and designers still make trade-offs. ‘The ideal foam is extremely light, very soft, and extremely bouncy,’ says Van der Zwet. ‘But the softer and lighter something gets, typically it becomes less durable.’
When comparing the durability of new foams to older foams, Van der Zweet says it’s important to distinguish between the energy or cushioning durability and the durability for general wear and tear.
‘The actual durability of the energy return in superfoams is good,’ says Van der Zwet. ‘Foams have improved well on this and now typically outlive other elements like outsole rubber or upper durability.’
When it comes to general wear, it’s slightly different. The risk of unwanted wear rises if the foam is unprotected, says Van der Zweet. Think lightweight race shoes with minimal outsoles.
‘If you step with your exposed Asics Flytefoam Turbo foam on very rough terrain, you can literally tear the midsole, says Van der Zweet. ‘This is less durable versus previous foams but is only true for those superfoams.’
So it’s even more important to use your shoes for their intended purpose.
Super shoes vs daily trainers
The range of foams, production processes and purposes also means it’s much harder to provide blanket lifespan advice across different brands and shoes.
‘All these polymers have strengths and weaknesses,’ says Jorma Seabourne, product director at low-environmental impact footwear specialists Hylo Athletics. ‘A PEBAX foam made three different ways would offer different levels of responsiveness and different levels of durability, depending on whether they're created by compression, injection or supercritical gas injection.’
The picture gets more complicated. A worn PEBAX midsole – as found in Nike’s carbon racers – past its optimal performance best, might still offer more energy return than a brand new EVA foam. So, your old, past-its-peak carbon racer might still have more bounce, what shoe makers call resilience, after 200 miles than your brand new daily trainer.
‘The testing we've seen shows supercritical foams retain the resiliency, the cushioning properties for longer than standard EVA,’ says Nikhil Jain, Director at Brooks’ Blue Line innovation team.
Seabourne suggests this is where perception plays a big role. Shoes some runners might consider well past their performance best, may still feel great for others. ‘I could probably get somebody who's been running in a Nike Pegasus, give them a 1,000km-old pair of Adios Pros, and they’ll think “these are good” because those shoes started on a different level,’ says Seabourne, who thinks much also depends on your needs and expectations.
‘For a racer looking for that 1%, if a shoe loses 5% after 300km that’s a massive deal. But if you're running a recreational parkrun, or just out and about, I don't think anybody's going to notice.’
So in theory, could your carbon racer become your daily trainer once it’s lost its optimal competitive edge? Possibly. The ‘death’ of a shoe isn’t as clean cut as it once was.
‘These new chemistries and compounds are unlocking new ways for a pair of shoes to interact with the runner over its lifespan,’ says Jonathan Hutnyan, Senior Project Line Manager, Performance Run Footwear at Under Armour. ‘Even towards the end of its life, a shoe still feels better than a lot of old products did out of the box.’
Do super shoes really lose their performance benefit?
When Nike’s Vaporfly carbon race shoes landed in 2017, they raised the performance bar. They also forced us to recalibrate our expectations around longevity. If 300-500 was the finger in the air for standard shoe staying power, 100 miles was often touted as the benchmark for bouncy racers.
Things got extreme at the end of 2023 when Adidas launched the Adios Evo Pro 1 as a single-race shoe. You could almost hear the planet groan. Not to mention runners’ bank accounts. A £300, one-race shoe felt like a step too far.
Unfortunately what makes super shoes so effective – big stacks of light, high-energy foams – is also their weakness. If lifespan is measured in optimal performance, research suggests the foams lose their edge.
Recent research at the University of Castilla-La Mancha compared modern super foams to traditional EVA in a new and worn state. Twenty two volunteers performed a running economy test in specially made carbon-plated shoes. The only difference between them was one had a PEBA midsole, the other EVA. After 280 miles, the PEBA shoe performed 2.2% worse while the EVA shoe lost nothing. And at 280 miles there was no significant difference in running economy benefits between the EVA and PEBA shoes. That magic super shoe effect had disappeared.
This could have a big impact on performance. A recreational marathoner wearing fresh super shoes could see a performance difference of around three minutes. ‘For a standard runner of 1.75m and 70kg with a marathon time of 3:00, improving 2% in running economy would mean improving 1.65% in performance. That means a final time of 2:57:05,’ says Victor Rodrigo-Carranza, who led the Spanish research.
Rodrigo-Carranza adds a big caveat though: not all super foams are equal. Plus, we don’t know what happens after 280 miles.
‘It would have been very interesting to wear the shoes up to 900km and evaluate the difference between PEBA and EVA,’ says Rodrigo-Carranza. Based on other studies, he believes EVA would lose all its cushioning at around 800-900km. ‘But I don't like to generalise because I’ve seen results from shoe companies where a model with EVA with nitrogen maintains the same cushioning with over 1,000km.’
It’s also worth reiterating that just because a super shoe isn’t providing peak performance that doesn’t mean it’s dead.
The bottom line
When it comes to knowing when it's time to replace your running shoes, the best advice seems to be this: listen to your body, rather than relying on arbitrary yardsticks. Don’t rush to bin shoes that could potentially play a different role in your running rotation when they lose their high-performance edge, either.
Cherish the evolving relationship you have with shoes over their lifespan and you can tread lighter on the planet without compromising your running.
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