Why
Running shoes do not work: Looking at Pronation, Cushioning, Motion Control and
Barefoot running.
The running shoe model needs to be fixed. Pronation, Motion
Control, Cushioning, and Stability shoes? Get rid of them all.
It’s not just barefoot running and minimalism versus running shoes, the
either/or situation many portray it to be. It’s much deeper than that. It’s not
even that running shoe companies are evil and out to make a profit. Shoe
companies may be accomplishing the goals they set out for, but maybe the goals
their aiming for are not what need to be done. The paradigm that running shoes
are built upon is the problem.
Running shoes are built upon two central premises, impact forces and pronation.
Their goals are simple, limit impact forces and prevent overprontation. This
has led to a classification system based on cushioning, stability, and motion
control. The problem is that this system may not have any ground to stand on.
Have we been focused on the wrong things for 40+years?
I’ll start with the customary statistic of 33-56% of runners get injured every
year (Bruggerman, 2007). That is kind of mind blowing when you think about it. Since
there are a ton of injuries going on, let’s look at what shoes are supposed to
do.
Pronation:
As said earlier, shoes are built upon the premise that impact forces and
pronation are what cause injuries. Pronation, in particular has been
constructed as the bane of all runners. We have become inundated with limiting
pronation via motion control shoes. The central idea behind pronation is that
overpronating causes rotation of the lower leg(i.e. ankle,tibia, knee) putting
stress on the joints and therefore leading to injuries. Running shoes are
therefore designed to limit this pronation. Essentially, running shoes are
developed and designed to put the body in “proper” alignment. But do we really
need proper alignment?
This paradigm on pronation relies on two main things: (1)over pronation causes
injuries and (2) running shoes can alter pronation.
Looking at the first premise, we can see several studies that do not show a
link between pronation and injuries. In an epidemiological study by Wen et al.
(1997), he found that lower extremitly alignment was not a major risk factor
for marathon runners. In another study by Wen et al. (1998), this time a
prospective study, he concluded that “ Minor variations in lower extremity
alignment do not appear conclusively to be major risk factors for overuse
injuries in runners.” Other studies have reached similar conclusions. One by
Nigg et al. (2000) showed that foot and ankle movement did not predict injuries
in a large group of runners.
If foot movement/pronation does not predict injuries or is not a risk factor
for injuries, then one has to question whether the concept is sound or
working...
Looking at the second premise, do shoes even modify pronation? Motion control
shoes are designed to decrease pronation through a variety of mechanisms. Most
choose to insert a medial post or a similar device. In a study by Stacoff
(2001), they tested several motion control shoe devices and found that they did
not alter pronation and did not change the kinematics of the tibia or calcaneus
bones either. Similarly, another study by Butler (2007) found that motion
control shoes showed no difference in peak pronation when compared to
cushioning shoes. Lastly, Dixon (2007) found similar results showing that
motion control shoes did not reduce peak eversion (pronation) and didn’t change
the concentration of pressure.
This is sort of a double whammy on motion control shoes. If excessive pronation
does not cause injuries to the degree that everyone thinks, and if motion
control shoes don’t even alter pronation, what’s the point of a motion control
shoe?
Cushioning:
Impact forces are the other major scoundrel of running injuries. The thinking
goes like this, the greater the impact force on the lower the leg, the greater
stress the foot/leg takes, which could potentially lead to injuries. To combat
this fear, running shoes, particular cushioning ones, are to the rescue. Let’s
take a look.
The first question is, do cushioning shoes do their job?
Wegener(2008) tested out the Asics Gel-Nimbus and the Brooks Glycerin to see if
they reduced plantar pressure. They found that the shoes did their job!....But
where it reduced pressure varied highly. Meaning that pressure reduction varied
between forefoot/rearfoot/etc. This led to the interesting conclusion that
their should be a shift in prescribing shoes to one based on where plantar
pressure is highest for that individual person. It should be noted that this
reduction in pressure was based on a comparison to another shoe, a tennis shoe.
I’m not sure that this is a good control. Basically, this study tells us that
cushioned running shoes decrease peak pressure when compared to a Tennis shoe.
In a review on the subject, Nigg (2000) found that both external and internal
impact force peaks were not or barely influenced by the running shoes midsole.
This means that the cushioning type does not change impact forces much, if at
all. But how can this be? I mean it’s common sense if you jumped on concrete
vs. jumped on a shoe foam like surface, the shoe surface is softer right? We’ll
come back to this question in a minute.
Impact Forces: The picture gets cloudier:
But it’s not as simple as described above.
In an interesting study by Scott (1990) they looked at peak loads on the
various sites of likely injury for runners (Achilles, knee, etc.). All peak
loads occurred during mid-stance and push off. This led to an important finding
that “the impact force at heel contact was estimated to have no effect on the
peak force seen at the chronic injury sites,” and led to speculation that
impact force did not relate injury development.
Further complicating the impact force idea is that when looking at injury rates
of those running on hard surfaces or soft surfaces, there appears to be no
protective benefit of running on soft surfaces. Why is this? Because of
something called pre-activation and muscle tuning which will be discussed
below.
Supporting this data, other studies have shown that people who have a low peak
impact have the same likelihood of getting injured as those with a high peak
impact force (Nigg, 1997). If you want to complicate things even further,
impact seems to be the driving force between increased bone density.
As a coach or trainer this should make sense. The bone responds to the stimulus
by becoming more resistant to it, IF the stimulus is not too large and there is
enough recovery.
Underestimating our Body: Impact forces as feedback:
Back to the question I asked earlier: How can impact forces not change based on
shoe sole softness and why isn’t running on hard surfaces lead to more
injuries?
The problem is, once again, we underestimate the human body! It’s an amazing
thing, and we never give it the credit it deserves. The body adapts to the
surface that it’s going to strike, if you give it a chance. The body adapts to
both shoe and surface adjusting impact forces via changes joint stiffness, the
way the foot strikes, and a concept called muscle tuning.
An example of this can be seen with barefoot running, the diminished
proprioception (sensory feedback) of wearing a shoe negates the cushioning of
the shoe. Studies using minimal shoes/barefoot have shown that the body seems
to adapt the impact forces/landing based on feedback and feedforward data. When
running or landing from a jump, the body takes in all the sensory info, plus
prior experiences, and adjusts to protect itself/land optimally As mentioned
above, it does this through a variety of mechanisms. Thus, you stick some
cushioned running shoe on the bottom of your foot and the body goes “Oh, we’re
okay, we don’t need to worry about impact as much, we’ve got this soft piece of
junk on our foot
One concept that needs to be further discussed is muscle tuning. It’s a concept
recently proposed by Nigg et al. in 2000. He sees impact force as a signal or a
source of feedback, as I stated earlier. The body then uses this information
and adjusts accordingly to minimize soft tissue vibration and/or bone
vibration. His contention is that impact force is not the problem, but rather
the signal. Muscle tuning is essentially controlling these vibrations via a
variety of methods. One potential mechanism is pre-activation. Pre-activation
is activation of the muscles prior to impact. In this case it serves as a way
of muscle tuning to prepare for impact and in addition can alter muscle
stiffness, which is another way to prepare for impact. Pre-activation has been
established with multiple EMG studies.
Shoes not only impact this, but surface type does too. As mentioned previously,
the change in running surface did not impact injury rates. Why? Probably
because the body adapts to running surface. In an interesting study measuring
muscle activity, O’Flynn(1996) found that pre-activation changed based on
surface. To prepare for impact, and presumably to minimize muscle/bone
vibration, when running on concrete pre-activation was very high, when running
on a soft track, not so much.
What all of this means is that the body adapts via sensory input. It has
several different adaptation methods. A shoe influences how it adapts. The shoe
is not doing anything to alter cushioning, it is simply altering how the body
responds to impact. It’s a significant mindset jump if you think about it.
Here’s the summary:
The type of shoe and material of the shoe changes impact NOT because of
alignment of the lower leg or because of changes in cushioning. Instead it
changes impact characteristics because it alters the sensory feedback
In conclusion on the cushioning concept. Well, what are we trying to cushion?
Heel impact forces have not been shown to relate to injuries, in fact in one
study low impact runners had a 30% injury rate compared to a 20% injury rate in
high impact runners. Shoe midsoles do not change, or marginally change impact
forces anyway. So, not only may cushioning not be the answer, the shoes might
not even be doing their job. But what about those shoe cushioning studies
showing improved cushioning with their new midsole?! Well, the majority of that
testing is done by using a machine to simulate the impact forces that you experience
during running. That means, yes it may cushion an impact more, but it doesn’t
take into account the role of the body adjusting impact based on feedback.
The reason cushioning doesn’t work? Because the body adapts based on feedback
and feedforward information. These results prompted one notable
researcher(Nigg,2000) to call for the reconsideration of the cushioning
paradigm for running shoes.
Barefoot running?
Quickly, this topic could not be complete without a brief mention of barefoot
running. An interesting thing to note is that the initial peak impact force is
absent in barefoot running when compared to running with shoes. What this means
is that, the impact forces look like (A) for shoes and (B) for barefoot. That
initial little blip in A is the initial impact force. There is a hypothesis
that this initial impact force is related to injuries.
A recent study by
Squadrone et al.(2009) compared running shoes, barefoot running, and running in
Vibram Five Fingers. They demonstrated reduced impact forces, shorter ground
contact and stride length, but increased stride frequency while running
barefoot (and in Vibrams) as compared to running with shoes. This is not
unexpected, but shows that running shoes do in fact alter our normal strides.
An interesting point is the reduction in stride length but increase in stride
frequency. Shoes tend to promote this longer stride at a consequence of ground
contact times and frequency. This happens because of changes in feedback
signaling, increased likelihood to land on heel stretched out, increased
weight, all of which lead to longer times on the ground. It’s interesting to
note that elite runners all have short ground contacts and high frequencies (as
demonstrated by the often quoted Daniels study of 180 strides per minute).
Tying this to the discussion above on the body controlling things based on
sensory information, when running barefoot, there is a higher degree of
stiffness in the lower leg. Increased stiffness can result in an increased SSC
(stretch shortening cycle) response, resulting in greater force on the
subsequent push off (2001). Dalleau et al. demonstrated that pre-activation
causing increased stiffness improved Running Economy. In his study, the energy
cost of running was related to the stiffness of the lower leg (1998)
Another recent study found that knee flexion torque, knee varus torque, and hip
internal rotation torque all were significantly greater in shoes compared to
barefoot. What does all of this mean? Potentially, this means more stress on
the joints in this area. Jay Dicharry put it best when he said:
“The soft materials in modern running shoes allow a contact style that you
would not use barefoot. The foot no longer gets the proprioceptive cues that it
gets unshod. The foot naturally accommodates to surfaces rapidly, but a midsole
can impair the foot’s ability to react to the ground. This can mute or alter
feedback the body gets while running. These factors allow a runner to adopt a
gait that causes the elevated forces observed above.”
The one thing that non-barefoot/heel strike proponents use to dismiss midfoot
striking/barefoot running is the Achilles tendon. They say, correctly, that the
load on the Achilles is higher in midfoot striking runners. The Achilles is
meant to take a large load. The problem is we’ve weakened the Achilles through
years of wearing shoes with their elevated heels. Essentially, we’ve created
the Achilles problem with the shoes meant to prevent it. The Achilles is
designed to operate in a rubber band like fashion. . During impact such as the
braking or contact phase of running, the achilles tendon stores energy and then
subsequent releases that energy via recoil during the take off phase of
running. The Achilles, can store and return approximately 35% of its kinetic
energy (Ker, 1987). Without this elastic storage and return, the oxygen uptake
required would be 30-40% higher! So, in terms of performance why are we trying
to minimize the tendonous contribution? It’s like giving away free energy.
Running shoes do not utilize the elastic storage and return as well as barefoot
or minimal shoes. More energy is lost with shoes than with barefoot running
(Alexander and Bennett, 1989). In addition, in some models of shoes, the arch
is not allowed to function like a spring. The arch of the foot can store around
17% of kinetic energy (Ker, 1987). Given these results, its not surprising that
running barefoot when compared to running with shoes is more efficient. Several
studies have shown a decreased VO2 at the same pace with barefoot running, even
when weight is taken into account. This should be no surprise as I mentioned
above, without elastic recoil VO2 requirement would be 30-40% higher. Running
in a minimal shoe allows for better utilization of this system.
So, the take away message is that shoes change natural mechanics to one that
creates mechanical changes that are not optimal for running fast (decreased
stride frequency, increased ground contact, decreased stiffness of the system,
decreased elastic contribution, and on and on).
Tying it together with elites:
Looking at elite athletes, when racing and training, they generally have higher
turnover, minimal ground contact time, and a landing that occurs closer to
their Center of Gravity. Since the majority of elites exhibit these same
characteristics while racing, it makes sense that this is the optimal way to
run fast. So, why are we wearing footwear that is designed to increase ground
contact, decrease turnover, and promote footstrike out in front of the center
of gravity? I have no idea.
Conclusion:
In conclusion, I’m not some fanatic saying everyone ditch shoes now. Chances
are you’ve been running in shoes for 20+ years. Your bodies done some adapting
during that time. You’ve got to gradually change if you want to undue some of
the changes.
The purpose of this article wasn’t to talk about the benefits of barefoot
running. Instead it was to point out the problems with Running Shoe
classification. It’s based on a cushioning/pronation paradigm that simply is
not as true as they want us to believe. That paradigm needs to be reevaluated.
It’s not founded on good science but rather initial ideas that made sense with
no science behind them, but upon further review may not stand up to testing. A
recent study found that using the good old shoe classification system that
everyone uses, had little influence on injury prevention in a large group of
Army Basic Training participants (Knapik, 2009). They concluded that selecting
shoes based on arch height (like all major running magazines suggest) is not
necessary if injury prevention is the goal. I guess that means the systems
broken…
Where do we go and how do we fix it? I have no idea. Sorry, no genius answers
here. My inclination is that we aim for letting the foot function how it is
meant to function, or at least come up with some shoe that may alter foot
mechanics but while still allowing feedback/functionality of the body. The
first step is looking at the foundation on which running shoes are built upon,
the motion control, stability, and cushioning paradigm. My take is that it
needs to be reevaluated. I’m going to end with something I’ve already said, but
it’s an important concept to get across:
The body is more complicated and smarter than we give it credit.
The type of shoe and material of the shoe changes impact or stride
characteristics NOT because of alignment of the lower leg or because of changes
in cushioning. Instead it changes impact and stride characteristics because it
alters the sensory feedback. The brain is a wonderful thing.'
