Traction Seems Far More Consequential Than Cushioning

Blog entry posted by trevize1138, Jun 12, 2018.

Barefoot TJ kindly asked that I start making blog posts. I've got a few things I've posted over on reddit that made for interesting conversation so I'll start putting them up here, too.

For the most part people have a very linear view of traction: more traction is better than less traction. I'm starting to see how this issue is far more complex when it comes to running. When running on different surfaces is discussed the focus is usually on hardness but that's just one of several factors that distinguish one surface from another. If I were to break it down for concrete vs dirt singletrack I'd list the following:
  • Concrete: Smooth, level, hard and high traction
  • Dirt singletrack: Varying degrees of texture from smooth to rocky to rooted, not level, varying degrees of soft to hard and overall a loose surface with varying degrees of traction
All of these properties of these two surfaces play a part in how you run on them. Hardness is just one and I'd argue the least consequential. It's also perhaps the least different between concrete and a singletrack trail as hard-packed trail and certainly rocky trail can be quite hard.

I believe the biggest difference is in how much singletrack can vary in its properties compared to concrete which is designed to be uniform throughout. An unpredictable surface, of course, forces you to watch where you step so you don't trip or twist an ankle. If you want to avoid impact injuries that's a very good thing because it means you'll take short, quick, careful steps. Running on concrete, therefore, doesn't encourage careful steps, especially if you put shoes on.

The only way you get better traction than rubber shoe tread on concrete is spikes on a track. And I don't think that's entirely a good thing. High traction is beneficial if your goal is to leverage that for forward momentum or acceleration. You can't really compete in a 100m dash without spikes. However, you can be fooled into over-striding on concrete with shoes because there's no feedback telling your body how bad that is. Cushioned shoes certainly block some of the sensation of impact to complicate matters but I'm discovering that just the traction itself plays a far bigger role. Your body isn't encouraged to take short, careful steps because the tread provides so much traction.

Think about the opposite of high-traction: running on ice. If you over-stride on ice your feet slide out in front of you landing you on your ass. If you push off too far behind you your feet slip out the other way and you land on your face. If you want to run on ice and don't have spikes you'll take very short, quick, careful steps. You won't be going anywhere fast, to be sure, but your body automatically reacts and adjusts to a safer movement.

Now think about traction between ice and concrete: loose dirt. You can run just about as fast on dirt as you can on concrete but over-stride too much and your feet start slipping. Push off too far back and same problem. Shorter, quicker, more careful steps are more encouraged than they would be on a high-traction surface.

That feedback you get from a loose dirt surface even in shoes is very similar to the feedback we unshod runners get on every surface. It's more than just avoiding impact and injury: it's about avoiding inefficient friction. If you're over-striding it's a braking move. On concrete you don't feel the braking effect if you've got padded shoes. Even if you have unpadded minimalist shoes you can still over-stride. In fact, when I first started out I was over-striding horribly in minimalist shoes but "I'm forefoot striking so I'm OK." I was still hitting the brakes like when I was heel-striking but now instead of shin splints I was getting pulled calf muscles.

The very nature of the loose surface itself encourages safer running form. Lots of people report how much nicer they like running in shoes on dirt than on concrete. I believe them when they say they're incurring less impact on dirt but very little if any of that has to do with surface hardness. It has a lot more to do with instinctive, involuntary movement adjusting to all the numerous differences in the properties of the surface.

Why it matters: runners are in danger of continuing to get injured by simply thinking cushioning is the end-all, be-all of injury prevention. Understanding the whole picture is far more helpful and you can only truly fix a problem if you properly identify the root cause. In the case of impact injuries the root cause is over-striding and it's far easier and more comfortable to over-stride in shoes, padded or thin, on concrete than any other type of running.

For minimalist and unshod runners this also explains why running on concrete in minimalist shoes can feel awkward compared to dirt or gravel. The tread under your feet blinds you to harsh, inefficient friction in your gait on high-traction surfaces. Some on barefoot/minimalist forums have even recommended getting shoes with a little bit of cushioning for running on roads which would only exacerbate the problem rather than addressing it.

This explains why so many of us have found the seemingly contradictory experience of enjoying unhod on concrete. You still have a lot of traction but with your skin exposed you now have the feedback of pain and discomfort if you engage in wasteful friction. That feedback encourages very similar movement to what you get on lower-traction surfaces.

Keep all of this in mind the next time you're finding paved surfaces challenging. Hardness is the least of the differences. That high level of traction can fool you.