Straight to it: based on my understanding of the current knowledge, the evidence and discarding all the logical fallacies, I can find no evidence and no rationale for any blanket recommendations for any ideal drop in a running shoe. Yet, everywhere you go there are some pretty strongly held opinions with lots of the typical rhetoric and propaganda as to what it should be. Given the strength of those opinions I was surprised to find how little evidence backs it up.
‘Drop’ has become the populist term for what the footwear industry normally calls ‘pitch’ and is the difference in the height of a shoe between the heel and forefoot. Some call this the ‘gradient’. To avoid confusion, ‘stack’ is the actually height of the heel and forefoot in the shoe, so heel stack, minus forefoot stack = drop. I probably should be using the more correct term, ‘pitch’, but will use the populist term ‘drop’ here¹.
Typically the drop of the vast majority of running shoes have been around the 10mm mark. I could find no research, rationale, theory or arguments as to why 10mm is the standard that has been used for a very long time by virtually all the traditional running shoe companies. It just appears to be what most runners are comfortable with. Historically, I am aware of a couple of anecdotes from industry insiders in which they did experiment with changing, but it was not accepted in the market.
Obviously, more recently with the minimalist trend, the term ‘zero drop’ has entered the vernaculum. I did a lot of searching and reading to see just what underpins the belief that this is better than a 10mm drop. I could find the very strong opinions, but no research evidence to back it up. I checked the websites of running shoe companies that market zero drop shoes to look for their evidence or rationale as well as the usual books (eg) and websites and found nothing substantial. A lot of them did mention the word “science”, but I could not find any science! To paraphrase what I found: the basic reasoning for zero drop is that it is more ‘natural’ and facilitates a more ‘natural’ running form away from a heel strike whereas a 10mm cushioned shoe tends to encourage the “unnatural” heel strike. That is all I could find to justify it. Anyone with a basic understanding of the ‘critical thinking’ or ‘logical argument’ fallacies will immediately recognize the flaw in that reasoning. It is the natural fallacy and is used all the time to argue that something is better because it is natural. Its a false argument. Just because something is natural does not make it better. Something may or may not be better for you because its ‘natural’, but to use that as an argument is a logical fallacy because there are plenty of natural things that are bad for you and plenty of unnatural things that are good for you.
I also came across a lot of use of the wishful thinking fallacy in regard to this as well. This is simply stating that zero drop or 10mm drop is best and just wishing it to be true. Those kinds of arguments are easy to deconstruct.
So basically, at this stage, nothing really underpins the concept of zero drop except a logical fallacy and nothing underpins the 10mm drop other than most runners are using it and we been doing it for a long time, which is also the logical fallacy of ‘appeal to popularity’ which also does not mean its right. It may or may not be right, but popular things have turned out in the past to be wrong, so no one can use that argument either.
(As an aside, while reading forum posts, blog posts and comments sections on this topic in the crankosphere blogosphere, I was surprised how often I read comments that could be interpreted that as though the 10mm drop was one great conspiracy by the running shoe companies to injure runners and affect their running form in a negative way! … go figure that out, given that the injury rates between traditional shod vs barefoot/minimalist and forefoot/midfoot vs rearfoot are pretty much the same ).
What evidence touches on this? While there is really no direct evidence (unless I missing something), there is some indirect research that can shed some light on this. There was one recent undergraduate project that found no differences in running economy between omm and 4mm drop running shoes. Another study did show running in a shoe with a 7cm or 4.5cm heel raise vs 1 cm is more uneconomical, but that hardly contributes anything to this discussion. Clarke et al in 1983 found no effects on rearfoot motion with changes in running shoe heel height (it would be good to know if there are any kinetic differences here, rather than just kinematic differences). Probably the best bit of research to inform this was by Reinschmidt and Nigg in 1995 in which they looked at changes in ankle joint moments with different heel heights in running shoes and they basically found no systematic differences, but they did report that “However, single subject analyses indicated that for two subjects the plantarflexion moments decreased with increasing heel heights“. For those two subjects this hypothetically, theoretically and overly simplistically means running in a 10mm drop would have less load to plantarflex the foot. This hypothetically and theoretically means that those 2 runners will have less load in the Achilles tendon (ie decreased injury risk for the Achilles problems) and the calf muscles do not have to work as hard (ie improved economy).
That last section points to what is probably the answer to what is the ideal drop: Its subject specific. Some runners are going to do better in a 10mm drop and some are going to do better in a 0mm drop (or the 4,6 and 8 in between), and don’t forget we are talking about very small differences of a few millimeters of a compressible material here. I have not touched on those issues of compression and drop and a cushioned zero drop shoe, may even be a negative drop shoe under load.
There are plenty of anecdotes of runners transitioning to zero drop running shoes and doing just fine and claiming to get less injury. Similarly, there are also plenty of anecdotes of runners not doing so well and claiming to get more injuries. But these are anecdotes and we know from the evidence just how unreliable anecdotes are when it comes to making blanket recommendations. This is the anecdotal fallacy.
For those who managed to understand what I wrote in the post on why one size does not fit all, its just as applicable here. Just look at the picture in that post showing the variation of the location of the subtalar joint axis; imagine the differing effects and lever arms that a 10mm vs a 0mm drop will have at that joint (let alone all the variations in the other joint axes across a group of runners!). You can then start to appreciate why the ideal drop is probably going to be subject specific.
Unfortunately, all we mostly have at the moment to determine this subject specific need is trial and error. We certainly need more work. What was it about the 2 subjects on the Reinschmidt and Nigg study above that changed? Was there anything “clinically” different in them compared to the others to help predict that they hypothetically and theoretically would benefit from a 10mm drop shoe? In the comments section on the post I did on supination resistance it was also speculated that those with high supination resistance probably should be in a higher drop shoe (and that speculation was based on extrapolating some research). It is more work, preferably more than just thought experiments along these lines that are going to help get to the bottom of determining in advance what the subject specific response is more likely to happen with different drops, so better recommendations rather than trial and error can be made. There is probably never going to be any research showing that one drop is systematically better than another (and I am sure this will disappoint the conspiracy nutters who think running shoe companies are deliberately trying to injure runners and affect their running form in a negative way).
On a personal note, I have drifted away from doing some of my runs in the NB Minimus (0mm drop) to the Saucony Kinvara’s (4mm drop). But that is my personal preference. Its what just feels right for me. I just don’t feel motivated and arrogant enough to evangelasize that because it works for me, that I have found the final solution and the holy grail and everyone should do it the way I preach.
While researching this, I was surprised to find a forum post I made 2yrs ago on this topic and had forgotten I made it:
“All we have is the nonscientific pseudoscientific propaganda from the ‘one size fits all’ school.
I don’t think there is a systematic ideal height. There is probably a subject specific ideal height … all we need is a way to determine it.”
… nothings changed! All we need is a way to determine it.
As always: I go where the evidence takes me until convinced otherwise, and thou shalt not commit logical fallacies when trying to determine it.
1. Sorry, David