Podcast Review: Running Shoes - Injury Prevention vs. Performance
#128 - Irene Davis: The Evolution of The Foot, Running Injuries, and Minimalist Shoes [The Drive: Peter Attia]
Reasons to Listen:
1hr 52min
Evolutionary look at human running and shoe development
The introduction of motion-control vs cushion-control shoes
Loading rates with different style shoes and strike patterns
My Take Aways:
Let’s start with some fun facts!
Over 24 hours, no land animal can cover more distance than humans
‘Humans’ have been running for ~ 2 million years
Humans have been wearing shoes for ~ 10, 000 years
During the running boom of the late 60s-70s people were beginning to run at a much higher rate. Due to a lack of training and proper adaptations, many people were getting injured, especially in the lower leg and foot.
Nike brought in a group of sport podiatrists that ‘analyzed’ these injuries and decided they were likely happening due to ‘too much motion’ or ‘too much impact’. From this, “motion-control” and “cushion-control” shoes were born.
Motion control shoes were designed for the low arch, flat foot, and over-pronators.
Cushion control shoes were for the high arch and rigid footed individuals.
There is a third category for ‘normal’ arches sometimes called a stability shoe.
These early injuries, especially to the achilles spurred on the development of a heel-toe drop to take some stress off the calf-complex.
BUT, does selecting a shoe to match your arch matter with regards to injury prevention?
Irene sites a study from 2014 where shoes were matched to people based on arch characteristics and then compared to a random distribution of shoes and found no difference in injury rates.
I guess not.
Irene states studies have shown that you actually land harder when you have extra cushion in your shoe and that extra support causes the intrinsic muscles of the arch to get weaker.
While this is true, the study I cited above is dependent on speed. There was no difference on impact loading between traditional shoes and maximalist shoes at 10km/hr paces.
Over the course of 12 weeks, it was shown that wearing orthotics decreases intrinsic muscle size by 10-17% in healthy feet.
Jason Tuori (see below), questions if this finding actually means anything with regards to injury rates.
Differences in landing patterns, forefoot strike (FFS) vs rearfoot strike (RFS) change the “rate of loading”. On a graph, the slope for a RFS runner will tend to be higher, meaning it takes less time to reach the peak force on every foot impact.
Landing on your forefoot has been shown to be the softer of the two (a lower slope) and Irene suggests that higher rates of loading are associated with increased injury risk.
The cue of “run softer” was given for 2 weeks and showed a 62% reduction in running injuries over the course of a year (in novice runners).
Match your shoe with your preferred foot strike pattern.
If you are already a forefoot runner or are transitioning to forefoot running then everything points towards being in a true minimalist shoe compared to a partial-minimalist shoe (see below for a standardized definition of minimalist).
Wearing a traditional running shoe and trying to run on your forefoot causes a series of mechanical changes, due to the extra bulk in the sole, that increase load on the achilles, increase the breaking force of each step (force in A/P direction) and increase the M/L force.
It sounds like it will certainly be less economical and Irene suggests will increase injury risk.
Partial-minimal shoes (some cushion, some heel toe-drop, etc) cause you to run more like you have a regular shoe on (ie. heel strike) but without the cushion… thus re-emphasizing the point that you should be matching a FFS with a minimalist shoe and a RFS with cushion.
This was shown in a study that compared regular running shoes, partial-minimalist shoes and minimalist shoes. The runners in partial minimalist shoes had significantly more injuries than the minimalist shoes.
An incremental transition to minimalist shoes is necessary even with healthy feet. If you rush into distance running you are almost guaranteed to run into an injury.
Wear them around while walking for a few weeks before even thinking about running.
A proposed progression is available in the linked document.
Is knee valgus a problem?
It depends….haha
Irene states that from her lab they see 2 main features of injury patterning.
High impact rates and general poor lower half alignment.
Poor alignment being defined as adduction and internal rotation of the femur and pelvic drop.
Irene was quick to state that injury-risk really depends on a number of factors as some runners have poor alignment and no pain while others have good alignment and lots of pain. Agreed.
She suggests thinking in a structure vs motor control vs dosage model.
Ie., even though motor control may be poor leading to a valgus collapse at the knee, the volume may be low enough to not cause pain.
Important to consider that even though the valgus moment is happening at the knee, pain can manifest at the hip, ankle or foot and not necessarily at the knee.
With regards to ITB pain, 2 studies, 1 retrospective and 1 prospective, determined that an increase in medial thigh angulation (adduction), hip drop, and tibial internal rotation were influential in its development.
For me, I think understanding that shoes can play a role in foot strike patterning and the rate of force development is important. I don’t think EVERYONE needs to be in a minimalist shoe, especially if you have no injury concerns and are running well. The idea that our ancestors ran on their forefeet and that is the ‘natural’ way of doing it misses the mark in some categories for me. As Irene mentions, it is painful to heel strike without cushion and leads to injuries. Being smart and resourceful creatures, we solved that problem by putting a cushion in the heel.
There are many variables when running that impact foot strike patterning and shoes are only one of them. Different speeds (cadence), different terrains, and different inclinations are all going to impact foot strike patterning.
It does seem like matching your choice of shoe with your preferred strike pattern is a useful starting place and these partial-minimalist shoes may not be the best idea.
If someone has a pre-existing injury to a certain body part then it may be favourable to recommend a foot strike pattern and subsequently an appropriate shoe to help them return to running. Using the shoe or foot strike pattern as a potential modifier of symptoms. Some examples below:
Achilles injury and client has been running in minimalist shoes. A switch to regular running shoes with a standard heel - toe drop and a heel strike pattern is going to take force off the achilles and decrease irritation in that region. This may allow them to continue running and eventually transition back to their preferred patterning/shoe as they recover.
Anterior knee pain and client has been running in maximalist shoes. Start with an increase in cadence… but a transition to forefoot striking (in appropriate shoes) will take load off of the knee and put more on the achilles complex. Again, once feeling better, they can transition back to their preferred patterning and shoe if they prefer.
These are obviously not extensive case studies but give an idea of how these modifiers may be used in practice.
Show notes here
#71 and 72: Jason Tuori: Footwear and The Running Athlete [The Clinical Athlete Podcast]
Reasons To Listen:
45 min each
Running shoe anatomy and properties
Running shoes and performance
Running Economy
My Take Aways:
Quick shoe anatomy lesson!
A sole has 3 layers that together make up the stack height. The difference in height between the heel and toe is called the drop. A standard drop is ~12mm but you can get shoes with a higher or lower drop, all the way to a 0mm drop.
Outsole - the tread
Midsole - foam
Insole - contact with your foot
A shoe has 4 main properties with regards to performance
Mass
A reduction in 100g of shoe corresponds to ~1% increase in running economy.
There is a tipping point though as running economy tends to be worse with barefoot running.
Cushion ie. foam
Compliance: amount the foam deforms (squishy)
Resilience: amount of energy returned by the foam (springy)
Shoe companies are trying to create a product that optimizes both qualities. In general, as compliance increases, resilience decreases. However, the new long distance running shoes have started using a Pebax foam that returns 87% energy. Up from the 66% energy returned by the traditional EVA foam.
As compliance increases so does limb stiffness, which decreases the metabolic cost of running. In other words, you don’t need to expend as much energy absorbing the contact with the ground.
Longitudinal stiffness - some research to suggest stiffer is better but largely unknown.
Comfort - current research topic to see if “feeling good’ improves performance.
Maybe???
The performance research around running shoes largely focuses on running economy (RE) which is the energy cost of running. More scientifically, RE is the oxygen consumption while running at a specific submax pace. An increase in RE is running faster while using the same amount of oxygen, thus an improvement in performance.
The impact of pace on RE and performance.
Less than 3m/s. 1% increase in RE = >1% increase in performance
Greater than 3m/s. 1% increase in RE = <1% increase in performance
5.5m/s (world class marathon pace). 1% increase in RE = 0.66% increase in performance
At marathon pace, 3% increase in RE = 2% increase in performance.
This works out to an improvements of minutes over the course of a marathon. Improvements in shoe tech may be a component for an official sub 2hr marathon sometime soon.
The 4% in Nikes vaporfly 4% was based on a 4% increase in RE compared to other comparable shoes.
Nike’s newest shoe the alphafly next% is said to have even better returns on RE than its predecessor. Rumour has it, improvements above 5% for some runners or ~1% more than their previous shoe.
Kipchoge was wearing some version of these bad boys in his latest race.
Strength and conditioning for endurance runners has been shown to improve running economy between 2-8%.
Who wants to work out when those new Nikes are calling your name. Just kidding, S&C is very important. Imagine how fast you could be with both!
RE is impacted by the shoe type and by the strike pattern. (RFS vs FFS)
RE worsens with a transition from RFS to FFS, at least in the short term
Does footwear reduce injury risk in running-related injuries?
Jason says simple answer, NO, but can be used to modify training load per stride and per session.
Running-related injuries are a complex system where shoes don’t play a huge role.
Errrrr, what was my whole writeup from Irene about…
Standardizes the definition of a minimalist shoe and provides a rating scale:
“Footwear providing minimal interference with the natural movement of the foot due to its high flexibility, low heel to toe drop, weight and stack height, and the absence of motion control and stability devices.”
0 (maximalist) - 100 (minimalist)
Should be used to purchase similar rated shoes or advise the modification of running load when changing shoes to reduce the likelihood of sustaining an injury in that transition
The authors suggest a 1 mo transition for every ~20 point change in shoes, however to be clear, the purpose of this study was not to create a timeline for running modification based on % change.
Shoe selection?
COMFORT
Feels similar to previous shoe
Minimalist Shoe Index
For me, the shoe index seems like a really good idea to make sure a new shoe isn’t going to be a huge change from the one you are wearing and a great way to advise patients on shoe selection. There are obvious performance enhancements in RE based on shoe selection. If you want to run faster, there’s a shoe for that. I agree that shoe selection isn’t going to be the make-or-break factor with regards to injury but, as I mentioned above, it seems like there is a way to optimize your footwear to your preferred strike pattern. Shoes can certainly be used to modify the load and with strike pattern, where that load is being distributed.
Thanks for taking the time to read!
