There's a rite of passage to earn your stripes as a serious runner. It isn't completing a marathon or achieving a sub-25-minute 5km. The reality is far less glamorous. It's called "runner's toe": a bruised and blackened toenail, or worse, lack thereof. It's almost guaranteed for long-distance runners (even with the best trail running shoes) but there are ways to lessen your chances of this stomach-churning side effect – and it could be as simple as sizing up your shoes.
It should come as no surprise to hear that an ill-fitting pair of running shoes is never okay. If there was ever a time to find the perfect footwear fit for your feet, it's when hammering paved roads or uneven trails for hours on end. A shoe that's too small can cause a range of problems, from blisters and knee pain to issues like Achilles tendonitis. (Not to mention the impact the wrong-sized shoe can have on your performance.)
Your standard shoe size might seem like a safe bet. After all, a shoe that's too big can cause just as many problems as a shoe that's too small. According to experts, however, your typical size usually won't cut it, and even a shoe that feels like the right fit probably isn't. Feeling bewildered about how trail running shoes should fit? Here we explore one of the most debated topics in the running world: whether or not you should size up your running shoes.
Should you size up running shoes?
It goes without saying, but make sure you try before you buy when choosing running shoes. To find the best fit, you should always head into a store to test a shoe first. Even then, a pair that feels right while standing and walking might not be up to scratch when you take to the trails or tarmac.
So how should a running shoe really fit? You'll need the shoe to feel snug around your heel, but there should still be a bit of room in the toe box. "The rule of thumb here is to leave roughly a thumb’s width between the toes and the front of the shoe," says Jeremy Stevens, running footwear buyer at Ellis Brigham.
To measure, remove the insole of the shoe and stand on it with your heel in position to see how far the insole comes out beyond your toes. "For some people, a full thumb’s width may be too much, but you’re definitely looking for enough space that there’s no risk of rubbing or stubbing your toe if you accidentally knock a rock or root," explains Jeremy.
The general advice, then, is to size up. According to Kaleigh Ray, Running Biomechanist and Certified Exercise Physiologist (ACSM) at Treadmill Review Guru, that generally equates to an additional 0.5 to 0.75 inches of extra space at the end of your shoe.
That said, you also want to avoid sliding back and forth in your shoe in order to keep those dreaded bruised toenails at bay. "The sliding around can also cause black toenails, blisters, and inefficiency during the push-off or toe-off," adds Frankie Ruiz, running coach and co-founder of the Miami Marathon at Life Time. The perfect shoe will be a happy medium: a tight fit that still allows wiggle room around the toes.
You also need to account for the terrain, which will be a more weighty consideration for trail running shoes vs road running shoes. "For more technical ground such as mountain terrain and fell running, a snugger fit will give better stability and precision," notes Jeremy.
Why is it important to size up running shoes?
Having extra room for your toes might seem counterintuitive when running. Surely you want to avoid repetitive impact from movement inside the shoe, such as your toes sliding forward? And beyond discomfort, you certainly don't want to disrupt any foot mechanics that could affect your kinetic chain of movement.
However, it's important to remember that your feet move with more force when running, meaning there's greater impact between your toes and the shoe. "Running inevitably puts more force through the gait cycle compared to everyday wear, making it more likely that your toes will suffer if they don’t have enough room," explains Jeremy. "Feet also tend to swell over the course of a run, and the longer you run for, the more likely they are to expand, pushing your toes closer to the front of the shoe."
"The extra space also provides protection for your toes when running downhill," adds Kaleigh. "Steep descents can cause your feet to slide forward in your shoes, knocking your toes against the front of the shoe."
How much should you size up by?
The debate is settled on sizing up, but by how much? Is a full size necessary, or is a half size more realistic? The answer isn't as clear-cut. "Whether you size up by a full size or half a size will depend upon the running shoe brand and how your shoes fit currently," Kaleigh explains. "I’ve had to size someone up three full sizes because they were wearing extremely tight shoes."
Your distance and terrain will come into play here, too. "In general it would be beneficial to size up half a size when buying running shoes, but a full size for ultra marathons," advises Matt Campbell, trainer and running coach at PRO Club. "You could also consider shoe inserts depending on your foot shape, which may help alleviate pressure on your toes."
The width of your foot will also play a part, with runners with wider feet more likely to need a full size up. "Runners with particularly narrow feet have the opposite problem, sometimes finding shoes which are the right length have too much volume and give a loose fit over the midfoot," adds Jeremy.
Lastly, don't forget to take the brand of shoe into account. With clothing, a size 10 in one shop can differ significantly from the shop next door, and the same is true for footwear. "For a long time, I had to size runners up an additional half-size for Asics and down a half-size for Hokas," says Kaleigh. "However, brands make changes to their fit all the time, and one model often fits differently from another."
"Depending on the shoe brand, sizing up may not even be necessary," adds Matt. "I recommend trying on multiple brands and models of shoes to see what fits and feels best. Be sure to try on with running socks and jog around in place."
If you're serious about your sport, there's little room for mistakes when choosing running shoes. Sizing up, even if only a half size, is the safest option, but it's always best to have your shoes fitted by a professional in a store to be sure. Perfect size secured, it's finally time for the fun part – breaking in your running shoes, a process that should now be far more comfortable.
