Clinical Analysis of Running, Running Footwear, and Injury Prevention/Performance. The Doctor(s) of Running, using knowledge of human movement, clinical biomechanics and performance to bring you cutting edge reviews, science and knowledge.

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Footwear Science: Running Shoe Fit

   As a website and group of Doctors of Physical Therapy, we get a great deal of questions on running shoe fit. From individual footwear, to brands, to even switching between different gender of shoes. After so many questions, we figured we would finally put together a post on running shoe fit. This is an extremely complicated and highly individual specific topic. Most people will probably know about general size measurements. This post is about some general rules for fit and especially about the difference between men's and women's shoes and whether or not you can switch between them. The answer is yes you can in some cases. Let's start with the simple stuff first.

Editor's Note: There are always exceptions to the rules below. As always, the true answer is "It Depends." We are discussing primarily RUNNING SHOES in this post. Hiking, Cleats and dress shoes are not within our area of expertise. 


Image from Amazon.com


US Shoe Sizes

    Most people in the United States are introduced to their shoe size by measuring their foot on a Brannock device. This has been the standard for measuring feet for many years. You can also measure your foot on your own and this handy chart from Running Warehouse (FOOT CHART) will help you convert your foot size in inches to whatever shoe size you want. The most important thing to remember is that you will probably have to go a half to a full size up from whatever you measure by yourself or what comes from the Brannock device. Most people are used to wearing their exact size in dress and normal shoes. For running, you will generally need a half to full size up to allow enough room for a little bit of foot movement, enough room for your toes and enough room to allow for swelling over longer miles. This obviously varies depending on the kind of shoe you are using and what you prefer. Some people prefer a little more room in their shoes and may want a half size bigger. Whereas those who want a tight fit for a racing shoe may want to go a half size down. It depends on you as the individual. For most people, when you first transition to running shoes, go a half size up. Or as people are often told in running stores, make sure you have a half to a full thumb's width between your longest toe and the end of the shoe (that is a general and non-researched based suggestion). Don't be married to the size as feet change in shape and length over the lifetime (Luxiomn & Goonetilleke, 2019). Additionally, sizing and widths vary greatly between different companies and even among different shoes in the same company! So again... when you ask what size may be best for you, the answer is... it depends. So if possible, always try the shoes on.

Mizuno Wave Duel GTZ - Racing Shoe currently available only overseas. 

International Shoe Sizes

   We at Doctors of Running do some international footwear reviews. I (Matt) have always been curious of the exclusive Asian market racing shoes that frequently do not make it to the US. This may revolve around the fact that firm, fast racing shoes do not sell as well in the US compared to traditional, highly cushioned trainers. Fortunately the release of cushioned super shoes like the Nike Vaporfly has been changing that. However it is still cool to see what is going on in other countries. The most common sizing you will see outside the US include UK sizing, Japan sizing and European sizing.

     For men, UK sizing is generally a half size down from the US number. For example, a US men's 10 is usually a UK size 9.5. A UK size 8.5 is a men's US size 9. Unlike the US, UK sizing doesn't change based on the gender. There is simple one sizing chart. Women's US sizes are generally 1.5 to 2 numbers larger than the UK size. So a US women's 11.5 is also a UK 9.5 (also technically a US men's 10).

Editor's Note: I have noticed some websites list a full size difference between a men's US size and UK size. Most however demonstrate a half size difference. From my experience, a half size has been more accurate, thus I go with what I was taught and my experience. Like many measurements, if I can't remember, I use Running Warehouse's measurements.

     For Japan (JPN), shoe sizes generally do not go up as high. Frequently, the largest shoe size you will find is the equivalent to a men's US 10 to 11. The conversation between US and JPN sizing isn't perfect, but generally a men's US 10 is a JPN 28. A men's US 9 is a JPN. Like the UK, there are not separate men's and women's sizing. So a US women's size 8 is a JPN 24.5 (men's 6.5) and a US women's size 11.5 is a JPN 28 (also US men's size 10).

    European sizes are very challenging. Not all sizes convert directly. In my usual US men's size 10, an EU size 44 is usually equivalent. When I wore Vivobarefoot shoes though, which used to be in EU sizes only, I was all over the place, from a 42 to a 43. Shoes that have more traditional shapes have been a 44 for me. So know there may be some variance. Every 1.5 sizes in the US (men) seems to line up with an even number EU size. A EU 46 is a US men's 11.5. A EU 42 is a US men's 8.5.  Good luck with this one. I try to avoid looking at EU sizing as best I can....



 New Balance Hanzo U 2E - another Japan only shoe, but I ordered the wide version.
Japan and Asia have a MUCH better availability of wide training and racing shoes.
 
Widths

    Widths vary greatly between companies. Different companies use different lasts, which is another word for shoe shapes. Some are wider, some are narrower. Traditionally, the most common width measurements are a B width for women and a D width for men. A narrow width is generally an A width for women and a B width for men. Meanwhile, a wide is a D width for women and a 2E (EE) width for men. There are many other variations of this. An extra wide for men is usually a 4E. Some companies may get more specific with a A width (slightly narrow from women), a C width (between a B and D width), an E width (between D and 2EE) and more. I have seen 8E once but they are very rare among running shoes. Most commonly among running footwear however, you will see A, B, D and 2E.


Image from StockX. Despite being Pink, these Next% are Unisex (men's) size).

Men's and Women's Sizing 

    This is where a great deal of questions come from. In US sizes, the difference between men's and women's footwear is about 1.5 sizes and B to D width. A US men's 9 is a US women's 10.5 and vice versa (just with a slight width difference). A B width is considered a normal woman's width by the industry and a D width is considered normal for men. Your actual results may vary.

     Few companies actually make men's and women's specific lasted shoes. This was unheard of until recently, despite the amount of literature demonstrating significant differences between the shape, sizes. There is clear research demonstrating that women have particular differences in the arch, forefoot, lateral aspect of the foot and the first toe compared to men (Wunderlich & Cavanagh, 2001). There are differences in the widths and lengths obviously between men and women's feet, but there are also height differences, although the research varies on this (Krauss et al., 2008; Lou et al., 2009). Given differences in bone structure, there are also differences in articular (joint) motions, hence the need for differences in flex grooves between men's and women's shoes (Ferrari, Hopkinson & Linney, 2004).

    Most footwear companies, until recently, participated in the act of "Shrink It And Pink It." Meaning that the majority of women's footwear was based on a men's last (shape) and simply narrowed, shortened and styled with women's colors. Some companies have been changing this, most notably Altra, Reebok and Asics, who have shoes with specific women's lasts. Some of Nike's performance shoes have women's specific lasts and the company seems to be improving. Mizuno is noted for gender specific flex grooves in their soles. And while the others may at least one women's specific shoe, they may not be as prevalent as you think.

    Given that most of the industry still does not make women's specific shoes, both men and women should feel comfortable switching between gendered shoes. For women with wider feet and men with narrower feet, don't be pushed away by a certain gender assignment to a shoe. Finding a comfortable fitting shoe may be one of the more important ways to prevent injury (Nigg et al., 2015). Thus both genders should feel comfortable switching. As mentioned earlier, there is about a 1.5 size difference between genders. So for a women looking at a men's shoe, add 1.5.  So a men's size 7.5 would be a women's size 9. For the male looking for a narrower fitting shape in a women's shoe, a women's size 10.5 will be a men's size 9 (narrow). While some may be concerned regarding different flex grooves, posting and more that are supposedly different between different gender footwear, remember that feet frequently do their own thing regardless of what you put them in (Nigg et al., 2017). Dr. Benno Nigg has pioneered the theory of the "Preferred Movement Pathway" and this suggests that although footwear may influence to a mild degree what happens, it is difficult to completely alter what the foot does. Each person has their own unique movement path, which makes designing shoes for a population challenging (generalization can be difficult). So again, like my advice previously, just find a comfortable fitting shoe and ignore the gender assigned to it for now.


The Brooks Hyperion Elite, another Unisex sized racing shoe

UNISEX Sizing

   After discussing differences between men's and women's feet and that many companies just make men's lasts and put pink colors on them for women, let's talk about unisex sizing.  Unisex sizing is always based on men's sizing. Unless told otherwise, women will have to add 1.5 sizes to determine their size. There is no research or public data on how these shoes are fitted, so unless told otherwise, expect a D width and men's last for most of these shoes.

 5 Step Fit Process - A Snails Pace
Image from A Snail's Pace, Southern California's Local Running Store

Getting It Right

    Now after everything we have discussed, how do you find the perfect fit? Since each person is different, you are going to have to find what works best for you. Some people like snug shoes while others don't like any pressure on their feet. Some people like having a wide toebox for their forefoot while others like a wide heel. Fortunately with the huge variety of running shoes out there, there is something for everyone. I do have some general suggestions for everyone however.

1.  Except for shorter races, shoes should not be too tight. There are a large number of sensitive nerves in the foot and ankle. Nerves do not typically do well with compression. Compression of the toes, metatarsals or any one of common nerve entrapment sites is asking for trouble. YOUR FEET SHOULD NOT GO NUMB WHEN YOU PUT ON A SHOE OR WHEN YOU RUN. That is not normal. So make sure you have adequate room through the shoe, but not so much that you slide around.

2. Make sure your toes have enough room! Shoes that are too narrow not only may cause excessive compression, they may alter the mechanics of the foot. More research is coming out suggesting that shoe shape may predispose people to certain pathologies, like narrow toeboxes and bunions (Ferrari et al., 2004). The foot works best when everything is lined up. The tendons and muscles have optimal length tension relationships, so changing that (ie smashing the toes together) may alter your mechanics, speed, strength and more. I will have a post in the future to dive into the research on this topic.

3. Again except for some people racing very short distances, make sure you have a little room between your toes and the end of the shoe. Feet do swell over runs and over the course of the day. That is why it is usually better to try on shoes in the evening compared to the morning. Shoes that are too short may predispose individuals to pathologies like hammer toes or shortened toe flexor muscles/tendons.

4. Find what works for you. Each person has a unique foot. It doesn't matter what your neighbor or best running friend says. You need to try these things and learn what works for your feet.

Conclusion

   Running shoe fit is not a straight forward. After reading this, hopefully you begin to understand how unique this experience is for each person. Not only are the feet of each person unique, but each company and individual models are unique in fit! If you forget everything else, remember that comfort is far more important than anything else. Don't be married to a specific size or even gender as many companies vary in width and lengths. While I am sure they (running companies) attempt to be consistent, the manufacturing process doesn't always work out that way. Unless you are in Japan, width options can be limited, so being a bit creative is key. Ladies, don't be afraid to wear a men's shoe if you have wider feet. Men, don't be afraid to wear a women's shoe if you have narrow feet (they often have better colors anyway....). Find what fits you comfortably so you can focus on your training, strength, speed and enjoyment of running!

Thanks for reading!
Editor's Note: As always, the views presented on this website belong to myself or the selected few who contribute to these posts. This website should not and does not serve as a replacement for seeking medical care. If you are currently injured or concerned about an injury, please see your local running physical therapist. If you are in the Los Angeles area, I am currently taking clients for running evaluations in person or via telehealth.

Matthew Klein, PT DPT OCS FAAOMPT
Doctor of Physical Therapy
Board Certified Orthopedic Clinical Specialist
PhD Student Movement Science and Rehabilitation
Fellow of the American Academy of Orthopedic Manual Physical Therapists

***Disclaimer My views are based on my extensive history in the footwear industry and years testing and developing footwear. If you are a footwear rep looking for footwear reviews or consultations on development, we are currently looking to partner with companies to assist, discuss and promote footwear models. Partnership will not affect the honesty of our reviews.

References

Ferrari, J., Hopkinson, D. A., & Linney, A. D. (2004). Size and shape differences between male and 
female foot bones: is the female foot predisposed to hallux abducto valgus deformity?. Journal of 
the American Podiatric Medical Association, 94(5), 434-452.

Krauss, I., Grau, S., Mauch, M., Maiwald, C., & Horstmann, T. (2008). Sex-related differences in 
foot shape. Ergonomics, 51(11), 1693-1709. 

Luo, G., Houston, V. L., Mussman, M., Garbarini, M., Beattie, A. C., & Thongpop, C. (2009). 
Comparison of male and female foot shape. Journal of the American Podiatric Medical 
Association, 99(5), 383-390.

Luximon, A., & Goonetilleke, R. S. (2019). Foot size and foot shape of children, adults and elderly. 
  In DHM and Posturography (pp. 295-319). Academic Press.

Nigg, B. M., Baltich, J., Hoerzer, S., & Enders, H. (2015). Running shoes and running injuries: 
mythbusting and a proposal for two new paradigms:‘preferred movement path’and ‘comfort 
filter’. British Journal of Sports Medicine, 49(20), 1290-1294.

Nigg, B. M., Vienneau, J., Smith, A. C., Trudeau, M. B., Mohr, M., & Nigg, S. R. (2017). The 
  preferred movement path paradigm: influence of running shoes on joint movement.

Wunderlich, R. E., & Cavanagh, P. R. (2001). Gender differences in adult foot shape: implications
  for shoe design. Medicine & Science in Sports & Exercise, 33(4), 605-611.

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