Updated with poll results below!
As I try to keep up with all the buzz on the release of Daniel Lieberman's much-anticipated barefoot running research, I'm spending more time on Lieberman's Harvard old-school-styled website titled Running Barefoot or in Minimal Footwear, which for sake of reference, I'll refer to as "Running BoMF."
One of the things I noticed on Running BoMF that I'd like to dig into is Lieberman's speculation as to why approximately 75% of shod runners heel strike. Per Running BoMF's section Foot Strikes & Running Shoes:
- It's comfortable. The shock-absorbing features cushion the force of impact. The graph below compares the forces that occur at the ground for a runner landing on the heel when barefoot (a) and in a running shoe (b). Note the initial impact transient, a nearly instantaneous and large increase in force that occurs as the heel comes to a sudden stop upon impacting the ground. The shoe reduces the force by about 10% and slows the rate of loading considerably. This, in addition to distributing the impact force over a larger area of the rearfoot, makes it comfortable to heel strike.
Thicker rearfoot cushioning than forefoot cushioning. This high heel makes it easier to heel strike because the sole below the heel is typically about twice as thick as the sole below the forefoot. So if your foot would tend to land flat when barefoot, it will land on the heel when in a shoe.
- It's stable. The shoe is designed to prevent too much movement such as pronation. This helps to make runners feel stable in modern shoes.
The thing that jumps off the page to me here is #2, "[If] your foot would tend to land flat when barefoot, it will land on the heel when in a shoe."
As I've moved away from both shod-running and shod-walking, I've observed substantial changes in how I strike the ground: in both instances, I've shifted towards using a forefoot strike. Striking with the forefoot has become secondhand now.
However, when I have to don shoes with a heel — and it doesn't take much heel to cause this — I find myself inescapably heel-striking. What gives? Well, my conclusion is the same as Lieberman's speculation: it's the elevated heels catching the ground when my foot reaches a near-flat clearance point.
Not that Lieberman was specifying any chronology here, but anyone who has ever watched young children or toddlers walk will tell you they walk on their forefoot — even in shoes (Granted, many of their shoes are moccasins without elevated heels like these). I contend that in a natural state, human beings would naturally learn to walk with a mid-foot or forefoot strike—just like little kids.
It's just that most shoes make a natural gait impossible*
Given that thicker heeled shoes can force a heel-strike, Lieberman's other speculations as to why shod runners heel strike naturally follow.
For one, given a cushioned heel that is getting in the way of a forefoot strike, you either fight the design of your shoe, requiring a sharper angle of approach at the forefoot so as to give the heel enough clearance to miss, or you just let the catch do it's thing and do your best to stay comfortable. I further speculat that even if you can manage a forefoot strike in a thick-heeled shoe, you're still going to lose some of the biomechanical efficiency that you get with a flat-shoe or barefoot because your foot won't be able to compress as far to the earth before ramming into the cushion of the shoe (And maybe this is why so many shoes try to capture that reduced compressibility via springs in the heels).
As for the third reason, this seems a natural extension given conditions #2 and #1: running shoes are designed to control your landing. With a monster spike in impact you get when running with a heel-strike, controlling that shock wave would be an important component in design as it's reverberation up your leg and foot could cause instability.
Anyway, I'm curious if anyone else has noticed that they forefoot strike while running or walking in VFFs or barefoot, but inadvertantly heel-strike in less minimalist footwear, and in particular as with shoes with elevated heels.
It's gotta be the shoes.
Update with poll results:
Below are the results of a poll that ran from January 28 through February 5 of approximately 100 minimalist footwear wearers. The results provide striking, albeit anecdotal, evidence that shoes with thick heels seem to force a heel-strike.
If you walk/run with a forefoot strike (barefoot or in VFFs), have you noticed that when wearing thick-heeled shoes they catch the ground, effectively forcing a heel-strike?
- Yes: 94% (95)
- No: 5% (5)
- N/A. I don't forefoot strike.: 1% (1)
Total Votes : 101
These two videos (barefoot and shod) showing an elite Kenyan runner in slow motion running in running shoes and then barefoot are used to illustrate how the angle of approach is the same in both instances, but in the shod-running video, the heel catches the earth, forcing a heel-strike. Lieberman uses this as an example to bolster his why-heel-strike-when-shod speculation on this page of his website.
Also, see Peter's video analysis of how individuals run shod or in VFFs here. I made similar comments on that post.
* Link is to a nine page read on the subject — I may go into more detail on this article at a later date as it is fascinating to me!