The Re-emergence of the Minimal Running Shoe

Transcription

[
clinical commentary
]
Journal of Orthopaedic & Sports Physical Therapy®
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Copyright © 2014 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
IRENE S. DAVIS, PT, PhD1,2
The Re-emergence of the
Minimal Running Shoe
M
inimal shoes are defined as those that have less cushioning
and stability than traditional running shoes. While the
minimal shoe is often considered a new trend in running
footwear, it has actually been around for a very long time.
It has only been in the past 50 years that footwear has progressively
evolved into the modern-day, elevated cushioned-heel, motion-control
shoe. While such changes were purported to assist in reducing running
injuries, these injuries have persisted at a
high rate. It has been suggested that this
modern-day footwear has significantly
changed the way we run and may contribute, in part, to the high rate of running injuries. This clinical commentary
describes the various aspects of the minimal shoe, including the history of running
footwear leading to its re-emergence and
how it differs from the traditional running
shoe in regard to biomechanics and injury
potential. Although this clinical commentary is not intended to be a comprehensive review of shod-running mechanics, it
TTSYNOPSIS: The running shoe has gone through
significant changes since its inception. The purpose of this paper is to review these changes, the
majority of which have occurred over the past 50
years. Running footwear began as very minimal,
then evolved to become highly cushioned and
supportive. However, over the past 5 years, there
has been a reversal of this trend, with runners
seeking more minimal shoes that allow their feet
more natural motion. This abrupt shift toward
footwear without cushioning and support has
led to reports of injuries associated with minimal
footwear. In response to this, the running footwear
industry shifted again toward the development of
will review the biomechanical studies that
have compared minimal shoes to barefoot
and elevated cushioned-heel shoes. In addition, it will discuss the progressive increase in running injuries since the 1970s,
as well as review the injuries associated
with different types of minimal shoes. The
importance of proper transitioning into
minimal shoes will be underscored, and
studies relating to transitioning to minimal shoes will be presented. Finally, the
application of minimal footwear beyond
running will be discussed, and areas of
future research will be suggested.
lightweight, partial minimal shoes that offer some
support and cushioning. In this paper, studies
comparing the mechanics between running in
minimal, partial minimal, and traditional shoes
are reviewed. The implications for injuries in all
3 conditions are examined. The use of minimal
footwear in other populations besides runners is
discussed. Finally, areas for future research into
minimal footwear are suggested. J Orthop Sports
Phys Ther 2014;44(10):775-784. Epub 11
September 2014. doi:10.2519/jospt.2014.5521
TTKEY WORDS: biomechanics, footwear, running
injuries, transitioning
A BRIEF HISTORY
OF FOOTWEAR
H
umans have been running essentially barefoot for the majority of
their evolutionary history. Homo
erectus, emerging nearly 2 million years
ago, is credited with being the first endurance runner.4 Homo erectus may have initially covered his feet for protection, using
materials found in the environment. The
oldest shoes recovered were found under
layers of volcanic ash in Fort Rock, OR
and radiocarbon dated to 10 000 years
old.6 These sandals were fashioned from
sagebrush bark woven into a flat surface,
and had rope ties to secure them to the
sole of the foot (FIGURE 1). It is clear that
the purpose of this shoe was simply to
protect the plantar surface of the foot
from the elements.
Shoes have undergone many changes
over the past 10 000 years. However, athletic shoes emerged in the early 1800s,
and their evolution was described in The
Sneaker Book by Vanderbilt.35 In 1832,
rubber soles were added to the bottom
of the leather shoes for greater durability. The next evolution in athletic footwear was the development of vulcanized
rubber, perfected in 1868, which allowed
for the formation of a flexible sole with
a tread. This sole was attached to a canvas upper, and Keds (mixture of “kids”
and “peds”) were introduced in 1916 by
the manufacturer Goodyear (FIGURE 2A).
They were advertised as “sneakers,” as
Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA. 2Spaulding National Running Center, Cambridge, MA. The author certifies that she
has no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article. Address
correspondence to Dr Irene S. Davis, Spaulding National Running Center, 1575 Cambridge Street, Cambridge, MA 02138. E-mail: [email protected] t Copyright ©2014
1
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[
clinical commentary
FIGURE 1. First documented footwear, made of
sagebrush bark, found in the Fort Rock caves in
Oregon. These shoes date back 10 000 years.
Copyright University of Oregon Museum of Natural
and Cultural History, photograph by Jack Liu.
they were quiet and allowed one to sneak
up on someone. In 1895, J.W. Foster and
Sons (now Reebok) added spikes under
the forefoot of the athletic shoe and developed the first running shoes (FIGURE 2B).
The father of the modern running shoe is
Adolf Dassler, who in 1926 introduced
the first customized running shoe. This
shoe had customized spike patterns and
lengths, depending on whether it was to
be used for sprinting or distance running.
Dassler’s shoes were worn by runners such
as Jesse Owens in 1936, and their success
later led to the formation of Adidas.
In 1964, Mr Onitsuka of Japan produced the first pair of cushioned running
shoes, the Onitsuka Tiger (FIGURE 3A),
which eventually led to the creation of
ASICS (Kobe, Japan).35 These shoes were
also marketed in the United States by Bill
Bowerman, a University of Oregon track
coach, and Phil Knight, one of his disciples. However, Bowerman and Knight
soon decided to form their own company,
which eventually became Nike. In 1972,
they developed their own version of the
Tiger that they named the Nike Cortez
(Nike, Inc, Beaverton, OR) (FIGURE 3B),
which was an instant success.
If we fast-forward 40 years, we find
that numerous athletic-footwear companies have emerged, including Brooks,
New Balance, Reebok, and Saucony, to
name a few.35 Throughout these years,
shoes have become increasingly more
cushioned and supportive. Jeff Johnson,
who worked for Nike between 1965 and
1983 and created the Nike name, was
]
FIGURE 2. Early sports shoes. (A) Keds sneakers that were fashioned from vulcanized rubber and a canvas upper
(courtesy of Keds). (B) First running shoes developed by J.W. Foster and Sons (now Reebok) in 1895 (courtesy of
Reebok). Adi Dassler (now adidas) later customized the spikes according to the distances to be run in them.
FIGURE 3. First cushioned running shoes. (A) Onitsuka Tiger (courtesy of Asics). (B) Nike Cortez.
able to shed some light on why this progression occurred (personal communication, March 12, 2014). Jeff began running
at 9 years of age in a pair of sneakers and
continued to run in high school. He remembers running in thin, solid-rubbersoled shoes with canvas uppers, recalling
that his training was of higher intensity
and much lower mileage than what is
typical today. He and his teammates developed what he referred to as “iron legs”
from running on hard surfaces with these
flexible, thin-soled shoes. What we have
since learned is that we have an incredible ability to modulate the stiffness of
our leg spring according to the surfaces
with which we come into contact.2,8,9
When training on hard surfaces, the leg
adapts by increasing its compliance, requiring increased demands on the muscular system. This may be what Jeff refers
to as iron legs. One point that Jeff was
very clear about was that running injuries
were rare at that time.
Running Injuries: The Impetus
for New Shoe Design
There were no reports of injury incidence
found in the literature in the 1960s, which
may, in fact, be indicative of a low occurrence of running injuries at that time.
However, reports of running injuries did
begin to emerge in the 1970s, when the
running explosion began (FIGURE 4). In
fact, a relatively newly minted magazine,
titled Runner’s World, conducted the first
survey of running injuries in 1971 (800
runners) and repeated it again in 1973
(1680 runners).6 This was followed by an
unpublished study conducted by Lloyd
Smith and colleagues in 1979 (974 runners) of injuries at a runner’s clinic at St
Elizabeth’s hospital in Massachusetts.6
These reports demonstrated an increasing percentage of runners sustaining
injuries. As is true today, knee injuries
were the most common injury reported
in these reports. However, the percentage of knee injuries in all runners increased from 17.9% in 1971 to 22.5% in
1973. Knee injuries as a percentage of all
injuries have also increased from 30.5%
reported in 19796 to 42% in 2002,33 one
of the most recent reports.
Jeff Johnson recounted that the first
reports of injuries in the Runner’s World
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Introduction of the
cushioned-heel
running shoe
(Onitsuka Tiger)
1963
1970
First runninginjury survey by
Runner’s World
Addition of motion
control and more
cushioning into
shoe
1971
1977
1973
1979
Formation of
Second runningNike; beginning injury survey by
of the running Runner’s World
boom
Third running
injury survey by
Dr Lloyd Smith
Emergence of the
first published
transition
programs
Introduction of Born to Run
the Nike Free published
2005
2006
2009
Introduction of the
Vibram Five Fingers
shoes; other minimalfootwear companies
begin to proliferate
2013
2011
First published case
report of stress
fracture in 2 minimalfootwear runners
FIGURE 4. Fifty-year timeline from the beginning of the cushioned-heel shoe to the development of transition programs to minimize injury during transition to minimal shoes.
study prompted Nike to collaborate with
3 pioneering sports podiatrists, Dr Steven Subotnick, Dr Harry Hlavick, and Dr
Dennis Vixie, who, seeing these injuries,
could provide some input into shoe design (personal communication, March 12,
2014). Though there were no empirical
data, these 3 prominent clinicians felt
that the injuries they were seeing were
related to excessive impact and excessive
foot motion, in particular, foot pronation.
Jeff reports that this was the clear catalyst for the addition of cushioning and
motion control in the running shoe. This
increasing trend has continued for over
4 decades.
With time, running shoes also became differentiated into 3 classifications:
cushioning, stability, and motion control
(Jeff Johnson, personal communication,
March 12, 2014). Cushioning shoes were
developed for runners with high-arched,
rigid feet that tended to excessively supinate or exhibit reduced pronation.
These shoes were relatively flexible, with
midsoles of lower durometer, a measure
of hardness. Stability shoes were designed with some cushioning and some
control and were intended for runners
with a neutral foot and normal mechanics. Motion-control shoes were intended
for runners with flat feet and were designed to control rearfoot and midfoot
pronation. They were constructed with
higher-density midsoles and additional
stiffening of the heel counter. Throughout these years, there have been countless running-footwear developments,
FIGURE 5. (A) Nike Free, the first modern minimal shoe. (B) Flex grooves in the sole allow for maximal flexibility
(www.nikeinc.com).
such as air soles, torsional springs, kinetic
wedges, etc. There has even been a shoe
touted as altering its stiffness to a female’s
menstrual cycle. Despite all of these technological advancements in the running
shoe, it has been reported that up to 79%
of modern runners are injured in a given
year.36 The purpose of matching footwear
to foot type was to assist in reducing injury. The validity of these claims was tested
by Knapik and colleagues13-16 in 3 large,
randomized controlled trials conducted
in differing branches of the military. In
all 3 studies, these authors reported that
matching footwear to foot type had no
influence on injury. Therefore, one is left
to question whether any of the technological developments in running footwear
designed for motion control and cushioning have been helpful in reducing injury.
The Rebirth of the Minimal
Shoe: The Nike Free
In the midst of the increasing technology,
Nike unveiled the first modern minimal
shoe in 2004. The shoe was developed
in response to feedback from Nike representatives, who in 2001 observed the
Nike-sponsored Stanford University
track team doing some of their training
barefoot. In fact, the legendary coach
Vin Lananna was quoted saying, “I believe that athletes that have been training barefoot run faster and have fewer
injuries.”21 The goal of the Nike Free was
to mimic barefoot running as closely as
possible. Jeff Pisciotta and a team from
the Nike Sports Research Lab embarked
on 3 years of research to better understand the mechanics of barefoot running
(Jeff Pisciotta, personal communication,
March 3, 2014). This team noted that
barefoot runners tended to land with
a flatter foot orientation and different
pressure distribution under their feet,
and exhibited greater hallux dorsiflexion at push-off. They therefore sought to
design a shoe that mimicked these characteristics. The Nike Free running shoe
represented a revolutionary change and
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[
clinical commentary
]
FIGURE 6. Some of the first modern, true minimal shoes with no cushioning and no motion control. (A) Huarache sandals of the Tarahumara indians in the Copper Canyon
of Mexico, fashioned from discarded tires and leather laces for tying them onto the foot. (B) Vibram FiveFingers shoes (courtesy of Vibram). (C) LUNA Sandals (Seattle, WA).
Courtesy of Ted McDonald.
a large departure from traditional running footwear. It was constructed with
an extremely flexible upper, including a
fully flexible heel counter. Additionally,
there was no arch support. The midsole
thickness and the heel-to-toe drop were
both reduced. Finally, the sole of the shoe
had so many deep flex grooves that it allowed the shoe to be rolled up into a ball
(FIGURES 5A and 5B). The shoe was designed on a numbering system, with 0
being referenced to completely barefoot
and 10 being their most supportive, cushioned shoe, the Nike Air Max 2000. The
first shoe they produced was the Nike
Free 5.0, which was halfway between
these conditions. Pisciotta and colleagues
fully realized that this shoe would place
greater demands on the foot and lower
leg. Therefore, each box of shoes came
with instructions on outlining a progressive transition to minimize injury risk.
The shoe was initially released only to
Nike Town stores and specialty running
stores, and only after staff attended educational seminars at Nike headquarters.
The shoe received a lot of publicity initially, but quietly fell into the background
of Nike’s extensive line of running shoes.
It eventually became more widely available, and a 3.0 version (less support) and
a 7.0 version (more support) were added
to the inventory.
The Impact of Born to Run21
While Nike Frees were fading from the
limelight, a new revolution in running
began. The catalyst for this movement
was the 2009 release of the bestselling,
epic nonfiction story Born to Run.21 Au-
thor Chris McDougall introduced the
world to the Tarahumara (meaning “running people”) indians who live in the
Copper Canyon of Mexico. He noted that
this reclusive group of ultrarunners did
not appear to be plagued with the injuries of most modern-day runners. More
surprising is that they were able to run
high mileage throughout most of their
lifetime and without the aid of modern
running-shoe technology. Their running
shoes were huarache sandals, consisting
of a rubber sole fashioned from discarded auto tires, held on with leather laces
(FIGURE 6A). They are similar in design
to the first sagebrush bark shoes dating
back 10 000 years, whose purpose was
simply to protect the sole of the foot from
the environmental elements.
Before the Born to Run21 explosion,
longtime barefoot runner Ted McDonald, aka Barefoot Ted, resided in Burbank, CA and did much of his training
in the steep, rocky, and hot foothills of
Los Angeles (Ted McDonald, personal
communication, February 3, 2014). As a
result, he had been experimenting with
all types of minimal footwear to protect
his feet. These included rope, yucca, and
rice-straw sandals. Unfortunately, none
of these were durable enough for his
running. However, in 2005, Vibram introduced the FiveFingers shoes (Vibram
SpA, Albizzate, Italy) (FIGURE 6B). They
were invented by Robert Fliri, a design
student from Vinschgau, who wanted
to “figure out a way to move around in
nature better.” They were originally marketed for yacht racers to maintain grip
on slippery decks while maintaining the
barefoot feel. Ted contacted the CEO of
Vibram to suggest that these shoes might
be the ideal minimal running shoe. The
rest, as they say, is history.
In 2006, Ted headed into the Copper
Canyon of Mexico in his Vibram FiveFingers to further his study of the “natural
selection of footwear in human socie
ties.” While he was there, a local Tarahumara indian, Manuel Luna, fashioned
him a pair of the huarache sandals out
of discarded automobile tires and leather
strapping. Little did Manuel know that
this would be the impetus for the launch
of Ted’s company, LUNA, and a line of
premium huarache sandals (FIGURE 6C).
The Minimal-Shoe Explosion
Although there was no empirical evidence, many of those who read Born to
Run21 were convinced that running barefoot or in minimal shoes would be the answer to their running injuries. Research
was revealing that most traditionally
shod runners land on their heels due to
the additional cushioning that cushioned
shoes offered.17,18 There were increasingly
more studies suggesting that the repetitive vertical impact loads associated with
a heel-strike landing might be detrimental to the musculoskeletal system.7,23,26,40
Habitually running barefoot, or in shoes
that lack cushioning in the heel, promoted more of a forefoot strike pattern,
which typically eliminated the vertical
impact transient.16 It appeared that a
paradigm shift in running footwear and
foot strikes was occurring. This led to
the emergence of a number of new footwear companies focusing on minimal
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running shoes, such as Inov-8, VIVOBAREFOOT (FIGURES 7A and 7B), and Altra. There is also a new line of huarache
sandals called the Invisible Shoe, which
consists of a flat bed and straps to hold
it onto the foot. Additionally, some of the
traditional companies began to develop
their own lines of minimal shoes, such
as the New Balance Minimus and the
Merrell foot gloves (Merrell Footwear,
Rockford, MI) (FIGURE 7C). Runners have
also begun to run in low-cost water shoes
such as the Teva Nilch (Deckers Outdoor
Corporation, Goleta, CA) (FIGURE 7D). The
common characteristics of all of these
shoes are no drop between the heel and
forefoot, no arch support, no midsole,
and either no heel counter or a flexible
heel counter. Basically, the shoe provides
protection for the sole of the foot and a
means for attaching it to the foot. While
many consider minimal footwear a new
trend, the shoes of Ron Hill, who won the
Boston Marathon in 1970 (FIGURE 7E), tell
a different story. Hill's shoes were custom
made by Reebok and named the World
10 shoe because Ron had broken two 10mile world records in them. These shoes
are more minimal than the majority of
the most minimal shoes of today, suggesting that we may be returning to an old
trend. In fact, when the minimal shoes
recently resurfaced, Ron’s response was,
“Hello, we’ve been here before … years
ago!” (personal communication, July 24,
2014).
BIOMECHANICS ASSOCIATED
WITH MINIMAL SHOES
M
inimal shoes have been designed to mimic barefoot running
as closely as possible. Most of the
studies that have incorporated true minimal shoes have found this to be true. For
example, Squadrone and Gallozzi32 compared the biomechanics between barefoot, minimal-footwear (Vibram Classic
FiveFingers), and traditional neutralshoe conditions. All participants were
experienced barefoot runners. These authors reported that the minimal-footwear
condition was similar to barefoot in strike
indices, vertical impact peaks, sagittal
plane foot and knee angle at touch-down,
as well as foot and knee excursions during
the support phase. Oxygen consumption
was also similar between these conditions. The only difference noted was that
stride length was longer when running in
the minimal shoe compared to barefoot.
However, in the traditional shoe, strike
index indicated a more posterior strike
pattern, the vertical impact peak was
significantly higher, and the foot was in
greater dorsiflexion and the knee in less
flexion at foot strike compared with both
barefoot and minimal-footwear conditions. Oxygen consumption was also significantly higher in the traditional shoe.
These results suggest that the minimal
shoe used in this study closely mimicked
the mechanics of barefoot running and
was clearly different from the traditional,
more cushioned shoe.
It is important to differentiate studies using habitual barefoot or minimalfootwear users compared to novice ones.
The majority of habitual barefoot/minimal runners do not land on their heels,15,16
most likely because it hurts to do so if
maintained over a prolonged period. This
typically results in lower vertical impact
forces and lower rates of loading than
when landing in traditional shoes, which
are associated with a heel strike in up to
89% of runners (FIGURE 8).17,18 However, in
a study of novice barefoot/minimal-footwear runners, vertical impact peaks and
rates of loading were significantly higher
in the barefoot and minimal-footwear
conditions compared with traditional
shoes.25 These novice runners likely did
not, on average, alter their mechanics
significantly during the single testing session. What is still unknown is just how
long it takes for someone to adapt to the
minimal-footwear condition, resulting in
a change of mechanics.
It has been shown that habitually
shod, rearfoot-striking runners who undergo a progressive, 12-week program
of running in minimal shoes (Vibram
FiveFingers) transition to a pattern that
FIGURE 7. The next wave of minimal running shoes.
(A) Inov-8 (Inoveight Ltd, Crook, UK) Bare 200x (with
permission from Inoveight Ltd); (B) VIVOBAREFOOT
(London, UK) Aqua Lites (http://www.vivobarefoot.
com); (C) Merrell foot gloves (courtesy of Merrell);
(D) Teva Nilch (water shoes that can be used for
running) (with permission from Teva). (E) Shoes worn
by Ron Hill, who won the Boston Marathon in 1970
(courtesy of Amby Burfoot). Note that these shoes
are more minimal than many of the minimal shoes
of today.
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[
clinical commentary
FIGURE 8. The vertical ground reaction force during running in traditional running shoes (left), minimal shoes
(middle), and barefoot (right). Note the similarity between the minimal-shoe and barefoot conditions and their
difference (additional impact peak) from the traditional-shoe condition. Abbreviation: BW, body weight.
is similar to barefoot running.20 This
includes a plantar-flexed ankle at foot
strike, shorter ground contact, and reduced knee flexion excursion. A related
study demonstrated a significant reduction in heel pressures following a 4-week
training program in Vibram FiveFingers.38 Both of these programs incorporated a foot and ankle strengthening
program as well. These studies indicate
that, with time, individuals do adopt a
more anterior strike pattern. More studies are needed to determine the exact
time of this transition and the permanence of these changes.
CAUTION: INJURIES
ASSOCIATED WITH
MINIMAL FOOTWEAR
A
long with the new movement in
minimal shoes have come reports
of injuries. The first report in the
literature was by Giuliani et al,11 which
described 2 runners with second metatarsal stress fractures following transition to Vibram FiveFingers minimal
shoes. However, both of these runners
incorporated this minimal footwear into
their running programs without any alteration in their running volume or any
preparation of their foot and ankle mus-
culature. Salzler et al29 reported a case
series of 10 experienced runners who
had been injured during their transition
to minimal footwear. All runners had
been injury free for 1 year prior to the
transition. Nine of the 10 injuries were
stress fractures and 8 of these were to
the metatarsals. The majority of these
runners transitioned very quickly (average, 0.7 months) and most injuries occurred within the first few months of
minimal-footwear running. This indicates that these injuries might be predominantly from poor transitioning, as
opposed to the minimal footwear itself.
Ridge et al27 randomized 17 runners into
a traditional shoe group and 19 runners
into a minimal-footwear group (Vibram
FiveFingers). The traditional-shoe runners continued with their typical training
mileage. The minimal-footwear group
was provided very liberal guidelines for
transitioning into the minimal shoes,
and was not given any exercises for foot
strengthening. Magnetic resonance images were taken at baseline and following a 10-week transitioning period. Ten
of the 19 minimal-footwear runners exhibited bony edema in their feet consistent with a stress injury (marrow edema
score between 2 and 4, with 4 being a
stress fracture). Interestingly, the major-
]
ity of these cases were subclinical (ie, the
subject had no symptoms). Most of these
were, again, to the metatarsals. Two were
diagnosed stress fractures, with the remaining diagnosed as stress reactions. It
is unclear whether those classified with
a marrow edema score of 2 (out of 4)
would have progressed to stress fracture
or were indicative of remodeling. However, this transition program was admittedly loosely structured and might have
allowed runners to transition too quickly.
Collectively, these injury reports underscore the need for a well-controlled, slow
transition to minimal footwear.
Unsupervised transition programs
should be conservatively designed to increase minimal-footwear running very
slowly. The transition program proposed
by Warden et al37 for returning to run
from a stress fracture is a very reasonable
one that can be easily adapted for transitioning to minimal footwear (FIGURE 9). To
follow this program, one must be able to
work up to walking briskly for 30 minutes
in minimal footwear. The 30 minutes are
then divided into three 10-minute intervals. In each of these 10-minute intervals,
walking is slowly replaced with running.
Rest days are provided and runners are
guided to progress only if they are pain
free at the current level. Therefore, the
transition is customized to the runner.
Running with less shoe support places
additional load on the foot. If progressed
gradually, this has been shown to increase
the strength of some of the foot and ankle
musculature.5 However, if the muscles are
not adequately conditioned, they are likely to fatigue quickly, and muscle fatigue
has been shown to increase strain of the
bones that the muscles support.22 Therefore, to further protect against injury, a
foot-strengthening program should accompany any transition to minimal footwear. This should include calf stretching
and strengthening (FIGURES 10A and 10B),
as minimal-footwear running is associated with more of a forefoot strike pattern, which loads the calf musculature.
To strengthen the intrinsic muscles of
the foot, towel curls and toe abduction
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(spreading) and adduction (squeezing)
exercises should be included (FIGURE 10C).
To address the muscles that support the
arch, foot doming should be performed
by pressing the toes down into the
ground and raising the arch (FIGURE 10D).
The importance of foot doming has been
highlighted in the study by Jung et al,12
demonstrating the significant increase
in activity of the abductor hallucis when
performing foot-doming exercises. The
abductor hallucis has been shown to play
an important role in the maintenance of
the medial longitudinal arch during static
stance.10 Others24 have shown that training with foot-doming exercises results in
a significant reduction in navicular drop,
an indication of less arch collapse.
Graduated Loading Program
Stage 0
Pre-entry to graduated loading program
Pain during walking in normal activities of daily living
Stage 1
Walk and jog stage (2 days loading, 1 day rest)
Level
A
Walk 30 min
B
Walk 9 min and jog 1 min (×3)
C
Rest
D
E
F
Rest
G
H
I
Rest
J
K
L
Rest
M
N
O
Rest
Stage 2
Jogging every second day
Level
A
Jog 12 min
B
Rest
C
Jog 15 min
D
Rest
E
Jog 15 min
F
Rest
G
Jog 17 min
H
Rest
I
Jog 17 min
J
Rest
K
Jog 20 min
L
Rest
M
Jog 20 min
Stage 3
Jogging (4 loading days in 1 week)
Level
A
Jog 25 min
B
Rest
C
Jog 25 min
D
Rest
E
Jog 30 min
F
Jog 30 min
G
Rest
Stage 4
Individualized running (5 loading days in 1 week)
Level
A
Running
B
Running
C
Rest
D
Running
E
Running
F
Rest
G
Running
Stage 5
Return to activity (individualized)
REGRESSION TO CUSHIONING
AND SUPPORT: THE
PARTIAL MINIMAL SHOE
I
t is likely in response to these
transition injury reports that shoe
companies have begun to produce partial minimal shoes. These are shoes that
may have a midsole, some heel counter,
some arch support, and a mild heel-totoe drop, but all to a lesser degree than
traditional running shoes. A comparison
of these footwear characteristics between
traditional, partial minimal, and minimal
shoes is provided in the TABLE. Partial
minimal shoes are touted as a safer compromise to the true minimal shoes. The
problem is that, despite having less midsole, these shoes have enough cushioning
that runners still tend to land on their
heels and experience impacts. For example, Bonacci and colleagues3 reported
that running mechanics in partial minimal shoes (Nike Lunar Racer, Nike Free)
were similar to running in traditional
running shoes (Nike Air Pegasus), but
statistically different from running barefoot. For example, stride length as well as
ankle and knee kinematics and kinetics
were generally similar between all shod
conditions, but different from barefoot.
This suggests that running in the partial
minimal shoes produced a similar pat-
FIGURE 9. Graduated loading program for transitioning from walking 30 minutes in minimal footwear to running
normal mileage. Reproduced with permission from Warden et al.37 Copyright ©2009 Elsevier.
tern to the traditional shoe, but a different one from the barefoot condition. In
another study, Willy and Davis39 reported that runners landed harder and with
more dorsiflexion when running in a partial minimal shoe (Nike Free) compared
with a traditional shoe. Further high-
lighting the potential danger of partial
minimal shoes, a recent prospective study
reported that runners in partial minimal
shoes sustained more injuries than those
running in true minimal or traditional
shoes.28 These studies together should
raise caution regarding the use of par-
9/16/2014 4:56:50 PM
[
clinical commentary
]
tial minimal shoes. Runners appear to
continue to heel strike in these shoes, yet
there is less cushioning to protect them.
The culmination of the research to date
also suggests that if a runner’s goal is to
adopt barefoot-like running mechanics,
he or she should transition slowly, and do
so with true minimal shoes. Alternately,
if runners are going to maintain a rearfoot strike pattern, they need to have adequate cushioning under their heel, and
they need to replace their shoes when the
cushioning becomes compromised.
THE APPLICATION
OF MINIMAL SHOES
BEYOND RUNNING
T
here have been a number of
studies recently suggesting that
shoes for the elderly should also be
more minimal. A study of women between the ages of 55 and 75 years determined that performance on the forward
reach test, the timed up-and-go test, and
the 10-meter walk test was better when
walking barefoot or in flexible, flat, thinsoled shoes compared to standard heeled
shoes.1 These minimal-type shoes appear
to be better for individuals with knee osteoarthritis (OA) as well. Shakoor et al30
reported that the knee loads associated
with the development and progression
of knee OA are reduced when walking
in thin-soled, flexible shoes compared to
either a control stability walking shoe or
a self-chosen walking shoe in individuals with knee OA. This same research
group31 has reported similar results when
walking barefoot, in flip-flops, or in thinsoled shoes as compared to clogs and
standard heeled shoes. Finally, there is a
prospective randomized controlled trial
in 56 elderly women with knee OA that
is currently under way.34 These authors
have provided thin-soled, flexible, minimal shoes to half of the women, whereas
the remainder will continue to wear
their own shoes. Measures of pain, function, and mechanics will be recorded at
baseline and at 6 months. Based on their
prior work, these authors hypothesize
FIGURE 10. Recommended foot and ankle exercises to prepare for minimal-footwear running. (A) Calf stretches
off a step; (B) calf raises off a step; (C) foot intrinsic exercises, including towel curls and toe spreading and toe
squeezing; and (D) foot doming, pressing down with the toes while raising the arch.
significant improvements in all variables
in the intervention group only. These
types of studies are needed to determine
if the concept of minimal footwear can
be extended to populations other than
runners.
Limitations
This clinical commentary presents a historical perspective on how running footwear has evolved from very minimal to
very cushioned and supportive, then reverted to minimal again. As some of this
9/16/2014 4:56:50 PM
TABLE
Characteristics of Traditional, Partial
Minimal, and Minimal Running Footwear
Characteristics
Traditional
Partial Minimal
Minimal
Arch support
Moderate
Minimal
None
Heel
24-32
12-24
0
Toe
14-22
10-17
0
Heel-to-toe drop, mm
>12
4-12
0
Heel counter
Stiff
Semi-flexible
Flexible/none
Sole
Stiff
Semi-flexible
Flexible
4.
5.
Midsole thickness, mm
history has not been documented in the
literature, personal accounts were solicited from key individuals in the running
community over the past 50 years. These
accounts are subject to bias and therefore limit the strength of this evidence.
Additionally, a focus of the commentary
was the relationship between footwear
and injury as it relates to biomechanics.
However, it must be acknowledged that
other factors not examined in this article,
such as fitness level, running experience,
age, culture, and environmental changes,
might also have played a role in injuries.
SUMMARY
I
t appears that the footwear pendulum has swung from the far left (our
barefoot/minimal footwear beginnings) to the far right (heavily cushioned
and supportive shoes) and back to the far
left (barefoot/minimal footwear), and is
now trying to find a settling point. Current running research suggests that the
mechanics of running in partial minimal
shoes are similar to running in traditional
shoes, but with less cushioning. Available
studies to date suggest that true minimal
shoes are needed to promote our natural barefoot running style. However, this
style of running places greater demands
on the foot and ankle, and transition injuries of the foot and lower leg have been
reported. Therefore, a transition must
be undertaken slowly and carefully to
allow proper adaptation. This is no different from taking on any new physical
activity that loads the body in a new way.
Unfortunately, simply putting a different type of shoe on does not automatically trigger a need to reduce training
and has resulted in injuries. Research
has also suggested that running in true
minimal shoes results in landing with a
flat or slightly plantar-flexed foot, with
less impact. As these impacts have been
associated with common running-related injuries, running in this manner with
minimal shoes may reduce injury risk.
However, prospective randomized controlled studies are needed to determine
if injuries are actually reduced with this
footwear. Additionally, research is needed
to determine the best way to transition
safely to reduce the incidence of injuries
during the transition period. Until then,
runners should err on the side of caution
by strengthening their foot and lower leg
and progressing their mileage slowly as
they transition to minimal footwear. t
ACKNOWLEDGEMENTS: The author would like to
6.
7.
8.
9.
10.
11.
12.
13.
acknowledge Erin Futrell, PT for her assistance
with the literature review for this article.
14.
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The Re-emergence of the Minimal Running Shoe

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