#168 Should I add carbon fiber stiffening insoles to my running shoes? - DOC

#168 Should I add carbon fiber stiffening insoles to my running shoes?

Today on the Doc On the Run Podcast, we’re talking whether or not you should add carbon fiber stiffening insoles to your running shoes.

Lots of running injuries are aggravated by bending of the toes. Plantar plate sprains, sesamoiditis, and Morton’s neuroma all get irritated when you bend the toes too much while you run. If you have any of these conditions it may help if you add some stiffness to your running shoe.

One way to help decrease pain in the big toe joint and the ball of the foot is too add a carbon fiber insert to the running shoe.

But believe it or not there are some right and wrong ways to use the carbon fiber inserts.

I recently got a call from a runner in Houston who was using some carbon fiber inserts in his running shoes. He was having a couple problems so he called asking questions.

The first question he asked was: “Should I put the carbon fiber insert on top, or under my shoe insert?”

Don’t forget, the insert comes in the running shoes is made of soft foam to protect you.

When you jump of a diving board, right, and you belly flop onto the water, you land flat and it’s an enormous amount of force. When you go with your feet first, it’s not as much force and it doesn’t hurt as much. 

When you take the carbon fiber insert, and you put it on top of the foam, it’s effectively like belly flopping onto the water every time because the carbon fiber is so stiff that it gives you all this peak force underneath the points of your foot, that really do have the most pressure normally. The foam in the shoe is supposed to absorb some of that. Now, of course, you have foam underneath the carbon fiber insert. A lot of people will argue, “Well, you have foam under there so it doesn’t really matter.” But that’s the thing, it actually does matter. 

If you put the foam insert that comes in the shoe, you take that out, put the carbon fiber inserts in, and then put your foam stock insert on top of it, it does give you a little bit of cushioning and will decrease some of the potential trouble for things like sesamoiditis, and for calcaneal bursitis, a bunch of stuff you don’t really care about. They’re problems you will get from too much pressure in one specific pressure point. That’s avoidable. 

Also, that foam insert, the sort of floppy flimsy one that comes in the shoe, it is perfectly designed, and cups, and fits, in the bottom of the shoe in a way that’s very precise. When you put that on top of the carbon fiber one, it really does do a lot to stop all the sliding and skidding around. 

On short runs, it really doesn’t matter that much. But when you’re doing long runs, or if you do any runs with hills, or your form starts to fall apart, you will wind up on the carbon fiber sliding forward and bashing your toes into the end of the shoes. You’ll wind up either with blisters or with black and blue toenails, and even lost toenails from beating them up too much. 

When this runner called, he said he had been placing the carbon fiber insoles on top of the existing stock inserts, but he felt like he was sliding around a bit on the slippery material while running. 

Well, most people do that. I see runners, frequently who get these inserts and then have carbon fiber inserts which they just stick them on top. Then I explain all that to them. 

There is another issue too. If you put the carbon fiber layer in the shoe, it actually stiffens it. It spreads the forces out more evenly across the bottom of the shoe, which will, in effect, make the foam last longer ’cause it doesn’t break down in one specific point as much. Right? It’s like if you lay down on the bed, it’s not that bad for the mattress, if you jump up and down on it with high heels, it’s high pressure in one spot and it wears it out sooner. That’s why you don’t want your kids jumping on your bed. 

The other thing, though, is that in terms of what it will do to you or your feet, as a runner, is that the carbon fiber is very good at adding more inherent stability to the shoe. It also increases, obviously, the length-wise stiffness of the shoe. If you’re prone to jamming your big toe joint, and you have hallux limitus or hallux rigidus where you get stiffness in the big toe joint, with just gets worse the more your bend it. 

If you have a plantar plate sprain or some other things where just bending the toes too much causes trouble, the carbon fiber inserts are fantastic at reducing the amount of bending in the foot because the stiff carbon prevents bending and that will help. 

The flip side of that is that when you’re used to running in very flexible shoes, you’re running form may change a little bit when you put them in because you then have a stiffer lever underneath you. You have to alter your gait a little bit because you don’t move your heel as easily off the ground and you don’t bend your toes as easily. Again, those are not necessarily good things. If you’re running with shorter strides, you’re not gonna do as much of that anyway. If your running as a heel striker, you’re more prone to bending the toes more ’cause your foot’s actually further behind you when you finally launch and take off again. 

In general, I think it’s a good idea, particularly if you like the shoes … Is one sort of rule, if you like the shoes but the shoes feel like they’re too flexible, or you’re starting to get issues because they’re not stable enough, adding a carbon fiber insole to the shoe can actually make it stiff enough that it does really help you and decrease a variety of different problems. It will, yes, it will alter your gait some. You just have to see whether or not do you like the way it feels. 

If you have extra flexible unstable shoes and you add carbon inserts it will make them a lot more stable. 

For example, I have done most of my Ironman races with Saucony Kinvaras. I’ve done marathons in Kinvaras. Kinvaras s are probably more similar to these minimalist type running shoes. They are just too flexible for my foot type for frequent long runs. 

You know, in general, I still do long runs Hokas or a standard sort of cushioning type running shoe. I don’t know. It’s like you really gotta be used to them to run long without getting injured when your forms falls apart. 

With the Kinvaras too, I will tell you if I’m not feeling good and super fit, I wouldn’t run a marathon in Kinvaras or minimalist lightweight shoes, you kind of have to be in good shape, and feeling good, and in good form, and all that sort of stuff, I think, to run in flexible shoes you’re talking about to do really long runs. 

Again, a simple strategy … One of the things I tell doctors, more than anything else, I’m like, “Look, I run in basically … I run in four different types of shoes. I use them for different types of run. Not because I think you need to match that shoe to that run, it’s ’cause I can’t remember.” I do speed work in Newtons, I do long runs in Hokas, I do long-ish runs in the Asics Gel-Nimbus, and I do fast runs in something like the Kinvara. I try to race in something like the Kinvara. 

That, also, is like cross-training for your feet. It spreads out the trouble. It gives you different stressors for different runs with different shoes because the different shoes will load you separately. 

When it comes to running shoe selection, runners think and want to believe there’s some secret weapon with the Hoka for long runs. Some secret weapon for track work or whatever. 

You just need to used different shoes to spread out the risk. You need to stress different things.

Because in over training, you are simply getting too much stress on one specific structure before you run again. If you stress them all differently, there’s less risk. Make sense?

You also have to match the amount of stiffness in the shoes to the stiffness of the surface. If you have running shoes with carbon fiber inserts and you’re running in Houston, they might be awesome for Memorial Park and they might be terrible at Allen Parkway. That’s because Memorial Park is mostly a soft crushed granite and dirt type running trail. But Allen Parkway is asphalt and concrete.

So if you had carbon fiber inserts to your shoes I may feel really good on soft surfaces but a little bit too stiff on hard paved surfaces.

Just experiment to see which combination of stiffness and your shoe, and stiffness in the running surface is right for you.


If you have a question that you would like answered as a future edition the Doc On The Run Podcast, send it to me, and then make sure you join me in the next edition of the Doc On The Run Podcast. Thanks again for listening!