Marathon Blisters Related to Pronation?

QUESTION:

Hi Doc,

I have just finished a marathon qualifier for an ultra coming up here in South Africa. I have always been pretty neutral footed, but with the tendency to pronate slightly. I have always had the odd blister after a very long run, but lately they seem to be worse and I am wondering if I am beginning to pronate more (can this happen over time?). I have taken a photo of some blisters that occur after a marathon. I don't like to get rid of them, I sorta let them callous for the season so its not so sore :-). Should I try pronation shoes? What are your thoughts? I use Nike Pegasus +28's. Really hope you can shed some light on this for me :-) 

Many thanks

ANSWER:

Blisters that pop up anywhere on the foot during/after a marathon are always the result of excessive pressure and friction. With excess friction the underlying layers of the skin begin to separate. Fluid accumulates and collects between the dermis and epidermis creating the fluid filled bubble that runners know as a blister. In the pictures here we can see that one blister has clear fluid and the other is dark. The dark blister implies that this is a collection of blood. This kind of blister is of course often referred to as a "blood blister." 

A blood blister insinuates more pressure or increased trauma, not just friction.

The location of the blister is important and helps a podiatrist figure out the cause. These blisters and calluses forming at the inside of the big toe joint. The medical term for this location is the "medial and plantar-medial aspect of the first metatarsophalangeal joint." 

All runners know the basic causes of blisters.  To be clear we will review:

1. Running shoes that are loose. The feet slide around with every foot strike and push off while running. The result of 26.2 miles of this is excessive friction producing blisters. 

2. Running shoes that are too tight. The feet are compressed against the inside of the shoes, increasing the risk of excess friction (with increased pressure) at parts of the shoe that move (such as the tips of the toes or ball of the foot where the break in the shoe occurs).  

3. Wet feet. Think twice about running through those garden hoses on the marathon course. Moisture in the skin can weaken the structure between the layers of skin, making blisters form with less friction that usually required. 

4. Starting and Stopping too much. If you are running with a walk/run approach, all of the starting and stopping actually takes more force (and produces more friction) than running at an even pace. This can increase your risk of blisters.  

There are other certain circumstances that can contribute to blister formation at the medial big toe joint. 

1. Pronation. As the foot pronates, the foot rolls inward, unlocking the joints in the mid-foot. The first metatarsal bone gets pushed up by the ground and the running shoe effectively twists right around the inside of the big toe joint. This of course creates excess friction and stimulated the formation of blisters during longs runs such as marathons. 

2. Bunions. Same forces at work as in excess pronation, with the added pressure at the bunion stick out and presses against the inside of the shoe. 

Solutions:

1. Blister-prevention socks that have 2 layers that can glide past each other. In effect, you beat up the socks instead of the skin.

2. Custom orthotics or over-the-counter inserts that support the foot, stabilize the subtalar joint and decrease pronation. If properly fitted and constructed, inserts can slow the pronation that contributes to the problem. 

3. Motions control running shoes. Stability running shoes decrease pronation with aggressive medial posting on a stable platform.  They are heavier, and stiffer. Beware-if you have high arches they can increase your risk of shin splints and stress fractures. 

4. Build mileage gradually. This gives the skin a chance to toughen up and form protective calluses without blistering.  

When in doubt. See a local podiatrist for a complete evaluation, running shoe analysis and gait exam to assess your running biomechanics. 

Dr. Christopher Segler, DPM a marathon runner, podiatrist and 10-time Ironman Triathlon finisher who is is Board Certified, American Board of Podiatric Medicine.  He believes the best podiatry practice combines cutting edge technology with the old-school convenience of house calls. He makes podiatry house calls for runners in San Francisco, Palo Alto, Sausalito, Pacifica, and Corte Madera. He also does remote consults for runners who live outside of the United States. If you have a question, you can reach him directly at 415-308-0833. You can learn more about running injuries at www.DocOnTheRun.com