Marathon Running Shoe Sizing: Why You Need to Size Up 0.5mm
Running causes your feet to swell. If your running shoes fit like your dress shoes, you're doing it wrong. Learn the 1cm rule for runners.
Running is one of the best ways to stay fit, but it's hard on the feet. Every time you land, your feet absorb three to four times your body weight. This impact, combined with the heat generated during exercise, causes your feet to swell significantly. This is why your casual shoe size is almost never your running shoe size.
1. The Science of the Swell
By the time you finish a 5k run, your feet can be up to half a size larger than when you started. If you start with a 'perfectly snug' fit, you will likely end your run with numbness, pins and needles, or the dreaded 'runner's toe' (blackened toenails). Professional runners always leave a 'buffer zone' to accommodate this biological reality.
2. The 1-Centimeter Rule
When standing in your running shoes, you should have roughly 1cm to 1.5cm of space between your longest toe and the front of the shoe. This might feel 'too big' at first, but it is essential. This space allows your foot to expand forward and outward without hitting the hard protective toe-cap of the shoe.
3. Fitting Checklist for Runners
- Heel Lock: Your heel should not slip up and down when you run. If it does, try the 'runner’s knot' lacing technique.
- The Midfoot Wrap: The shoe should feel secure across the top of your foot but not so tight that it cuts off circulation.
- Sock Choice: Always fit your shoes wearing the specific athletic socks you plan to run in.
Conclusion: Better safe than sorry
When in doubt, go up half a size. You can always tighten the laces or wear slightly thicker socks, but you cannot create space where there is none. Protect your feet from impact and give them the room they need to perform at their best.