The Monday Shakeout: Shoe Durability
By Matthew Klein
Welcome to our first edition of the Monday Shakeout! This is a new segment where our team can drop a few thoughts we've been having recently about a running-related topic. This week Chief Editor Matt Klein dives into the topic of outsoles and durability.
One of the more frequent sets of questions we get at Doctors of Running
is about shoe durability. People will ask how long shoes last, when they
should replace them or why shoes seem to not last as long as they used
to. These are questions I also ask frequently because I have always worn
out shoes quickly and am the "standard of durability testing" amongst
the whole team at Doctors of Running. The answer to all of these is (of
course) "it depends" but there are some valid points worth addressing to
understand why.
Different shoes will last different amounts of time for different people. Shoes with thick amounts of durable outsole rubber will last longer than shoes without outsoles that have exposed midsole on the bottom (like the Under Armour Velociti Elite). People that land softer or less aggressively will wear down their shoes slower than someone who pounds the ground, scuffs one or both shoes during the swing phase of gait (like me) or lands on a part of the midsole that has less durable material. If you are someone who consistently wears out shoes quickly, chances are you are going to continue to do so and you will likely find an average limit with some experience (mine tends to be 150-200 miles).
The shoe industry has frequently cited 300-500 miles as being the time when you should replace your shoes. There is no evidence behind this unfortunately and current evidence suggests that all shoes will break down and how they break down will depend on the individual using them to a degree. There are some shoes that will break down at 50 miles and others at 500. Defining the phrase "break down" may be helpful here and using the term "failure" instead. A shoe is done when it no longer works for the runner, be it due to a loss of cushioning or a wear pattern that places undo/abnormal stress on the runner.
With increased wear and use, running shoes lose their cushioning properties (Brueckner et al., 2011; Chambon et al., 2014; Morio et al., 2009; Wang et al., 2009. The ability of a midsole to compress is called compliance. The ability of a midsole to bounce back from being compressed is resilience. With increased wear over time, the midsole compresses more and loses its resilience, compliance, and cushioning properties (Chambon et al., 2014; Lin et al., 2022; Verdejo & Mills, 2004). How quickly the midsole losses this ability depends on the type of foam used.
Under normal conditions, EVA foams tend to break down faster, PEBA foams tend to be a bit more durable and TPU are even more durable (Lin et al., 2022). When you introduce foam blends (most EVA midsoles are not pure EVA and are now combinations of foams), this changes the durability. Runners do adapt to this (usually) and will begin to compensate for these changes until they cannot (Brueckner eta l., 2011). At that point either the shoe will be too uncomfortable or they will experience some kind of bodily/tissue stress that if ignored may result in an injury. Certain people will be more or less adaptive or sensitive to this, which is why some people may be able to get 1000 miles out of a shoe while others will get 100.
Writer's Note: Some unpublished research (grey literature) I participated in while in college under the direction of Dr. Heidi Orloff suggested that all shoes, regardless of price, broke down at approximately 100 miles. The durability after that was more dependent on the individual's ability to compensate for the changes occurring in the shoe. This was done well over a decade ago and it would be interesting to see if the same thing proved to be true with foam blends, PEBA and other newer foams.
So to finally reiterate the answer to the above questions, how much mileage each person will get out of a shoe will depend on both the shoe and the person. Some shoes now are less durable as they are being made with softer foams, less outsole rubber to save weight and other components that cause faster breakdown. Older shoes tended to use harder foams with far more extensive outsole rubber. These of course were extremely heavy and uncomfortable, so a price has to be paid for greatly reduced weight, cushioning and comfort. There are several shoes that are still plenty durable but you will need to look for a shoe with a better foam that has extensive outsole rubber. Across all shoes, when they start to become uncomfortable, feel like they have no cushioning left (if they are supposed to and you want that. Minimalist shoes do not count), cause you pain or abnormal symptoms, have holes/wear the comprises the structural integrity of this tool, then it is time to get a new pair.
References
Brueckner, K., Heidenfelder, J., Odenwald, S., & Milani, T. L. (2011). Mechanical and biomechanical characterization of running shoes with different midsole materials before and after aging. Footwear Science, 3(sup1), S18-S20.
Chambon, N., Sevrez, V., Ly, Q. H., Guéguen, N., Berton, E., & Rao, G. (2014). Aging of running shoes and its effect on mechanical and biomechanical variables: implications for runners. Journal of Sports Sciences, 32(11), 1013-1022.
Escamilla-MartÃnez, E., Gómez-MartÃn, B., Fernández-SeguÃn, L. M., MartÃnez-Nova, A., Pedrera-Zamorano, J. D., & Sánchez-RodrÃguez, R. (2020). Longitudinal analysis of plantar pressures with wear of a running shoe. International Journal of Environmental Research and Public Health, 17(5), 1707.
Lin, S., Song, Y., Cen, X., Bálint, K., Fekete, G., & Sun, D. (2022). The Implications of Sports Biomechanics Studies on the Research and Development of Running Shoes: A Systematic Review. Bioengineering, 9(10), 497.
Morio, C., Guéguen, N., Baly, L., Berton, E., & Barla, C. (2009). Relationship between biomechanical variables and sole viscoelasticity with fresh and fatigued running shoes.
Verdejo, R., & Mills, N. J. (2004). Simulating the effects of long distance running on shoe midsole foam. Polymer Testing, 23(5), 567-574.
Verdejo, R., & Mills, N. J. (2004). Heel–shoe interactions and the durability of EVA foam running-shoe midsoles. Journal of biomechanics, 37(9), 1379-1386.
Wang, L., Xian Li, J., Hong, Y., & He Zhou, J. (2010). Changes in heel cushioning characteristics of running shoes with running mileage. Footwear Science, 2(3), 141-147.
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