Barefoot-like designs challenge footwear conventions: MBT+Nike Free

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Biomechanics Magazine February 2007

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Barefoot-like designs challenge footwear conventions

Shoes from Nike and Swiss Masai increase activity of small muscles,

which could trim runners' times or decrease OA pain.

By: Jordana Bieze

The idea of going barefoot means different things to different

people. To some, the absence of footwear means one less barrier

between man and nature, feeling the warmth of sand between one's

toes or the coolness of dewy grass tickling one's soles. To others,

it means one less layer of protection from the heat of a sun-

scorched sidewalk, the bits of broken glass lurking in the sand or

the animal droppings that help keep the grass so green. Some think

of going barefoot as losing not just protection, but also the

stability and cushioning that footwear provide. And some think of it

as an opportunity to use muscles in the foot that would otherwise

lie fallow.

As one might expect, there aren't a lot of footwear manufacturers in

the last category. But two shoe designs, the Nike Free and the Masai

Barefoot Technology shoe from Swiss Masai, are now being marketed to

individuals who want the benefits of going barefoot-both the feeling

of freedom and the biomechanical challenge-along with some degree of

protection. Research confirms that both shoes alter gait patterns

and increase muscle activity. It remains to be seen, however,

whether those changes result in injury prevention or improved

performance. Practitioners and research also remain unclear as to

just which athletes or patients might benefit from the use of the

footwear, and for which individuals the unorthodox designs might

pose a risk.

Barefoot background

Barefoot running, made famous by such athletes as trackster Zola

Budd and marathoners Abebe Bikila and Charlie " Doc " Robbins, not

only has something of a cult following among hard-core runners but

also has long been used as a training tool by coaches. And barefoot

walking isn't just for the beach any more, judging from the number

of Web sites extolling the delights of shedding shoes for everything

from driving to hiking.

Given this level of popularity, surprisingly few recent studies have

specifically examined the biomechanics of barefoot walking or

running-with much of what is known in this area dating back more

than a decade. A February 1985 study published in Medicine and

Science in Sports & Exercise found that barefoot running was more

economical than shod running in terms of aerobic cost, and was

associated with less angular displacement of the knee. In the April

1987 issue of MSSE, Canadian researchers documented that barefoot

running was characterized by deflection of the medial longitudinal

arch not seen in shod runners. An April 1991 study by Swiss

researchers, published in the same journal, reported that running

shoes decreased torsion angles and increased pronation angles

compared to running barefoot, but those results were disproven in a

November 2000 study that used more accurate marker placements. The

follow-up study, published in the Journal of Biomechanics, found no

significant differences in calcaneal or tibial movement between

barefoot and shod running.

Following the lead of researchers from the 1980s, more recent

studies have also offered evidence for active adaptations on the

part of barefoot runners. Belgian researchers reported in the March

2000 issue of the Journal of Biomechanics that barefoot running was

associated with flatter foot placement and lower peak heel pressures

than shod running, and suggested that the latter change was the

result of the former. In the September 2005 issue of the

International Journal of Sports Medicine, French researchers found

greater preactivation of the triceps surae muscles and lower impact

peaks associated with barefoot running. And in the August 2003 issue

of the Journal of Biomechanics, investigators from the University of

Calgary reported that the timing and intensity of the tibialis

anterior muscle firing was altered with the use of running shoes.

Recent studies have also focused on the effect of barefoot running

on shock absorption further up the kinetic chain. In a study

published in the August 2001 issue of IJSM, Austrian researchers

found that running shoes significantly decreased shock transmission

and improved muscle response at the spine while jogging compared to

a barefoot condition. But a July 1995 German study of a single

subject with instrumented hip implants, published in the Journal of

Biomechanics, revealed that loads at the hip were lowest while the

subject was barefoot and that softness of footwear materials did not

translate into load reductions. And a September study from Rush

Medical College in Chicago found that peak joint loads at the hip

and knee were significantly lower in 75 patients with knee

osteoarthritis while walking barefoot than while walking in shoes;

those findings were published in Arthritis & Rheumatism.

" The concept is that shoes take over certain functions, so some of

the muscles don't have to do the work that they would normally do, "

said Benno M. Nigg, PhD, director of the Human Performance

Laboratory at the University of Calgary. " They can provide intrinsic

stability, and because small muscles usually have a lever arm that

is smaller with respect to the joint, loading is reduced when these

muscles are active. This should have an effect on performance. "

Free thinkers

The idea to make a Nike shoe for people who prefer not to wear

running shoes came, in a roundabout way, from Vin Lananna, then-head

coach of the Stanford University track and field team. Since the

university had a partnership with Nike, company designers and

researchers were on hand during workouts to observe how their shoes

were being used-and noticed that, at times, Lananna had his athletes

run barefoot, claiming that it improved performance. Likely taking

into account that Lananna wasn't the only coach enamored of barefoot

training, Nike gave researchers the go-ahead to see if they could

develop a footwear product that would serve the same purpose.

On a sunny day in June 2001, the researchers used high-speed video

cameras and pressure sensors to analyze 10 male and 10 female

competitive runners on a natural grass field, running barefoot at a

pace equivalent to a seven minute, 30 second mile. They found that,

relative to running shod on a hard surface, barefoot running on

grass resulted in differences in timing of foot contact, pressure

progression pattern, distribution of contact area, magnitudes of

peak pressures, foot angle relative to the surface just prior to

contact, metatarsophalangeal joint range of motion, and range of

plantar flexion right before toe-off.

" The foot was in control, " said Jeff Pisciotta, senior researcher

and biomechanist at Nike's Sports Research Laboratory in Beaverton,

OR. " I had thought variables at the knee would have changed due to

lack of cushioning, such as more flexion for shock absorption, but

all the changes were at the foot and ankle. That made us start

thinking that when you put a shoe on, it starts to take over some of

the control. "

The Nike Free 5.0 running shoe, introduced in 2004, was designed to

provide about half (i.e., five out of 10) the stability of a

conventional running shoe-stopping short of allowing full range of

plantar flexor or MPJ motion, for example. It features a very thin

upper material, no heel counter, and an outsole segmented by deep

grooves to allow for flexion. A cross-training version of the 5.0 is

now available, along with a 7.0 version for heavier athletes who

need more stability; a 3.0 version is in the pipeline.

Two clinical studies of the prototype Nike Free were conducted by

researchers at the University of Cologne and presented in the summer

of 2005. In one study, presented at the International Society of

Biomechanics' Symposium on Footwear Biomechanics just prior to the

July 2005 meeting of the ISB in Cleveland, OH, 25 athletes used the

Nike Free shoes for warm-up only (then switched to conventional

training shoes for the majority of a workout) three or four times

per week over a five-month training period. A control group of 25

athletes used only conventional training shoes for the same period.

At the end of the intervention, the researchers found that MPJ

flexor strength, plantar flexor strength, dorsiflexor strength, and

inversion moment had significantly increased from baseline in the

experimental group but not in the control group. In addition, the

cross-sectional area of the flexor hallucis longus and flexor

digitorum longus significantly increased in the experimental group.

In the second study, presented at the 2005 ISB meeting, an

experimental group of 50 subjects wore the Nike Free shoes while

performing a set of specific exercises (20 to 30 minutes) four times

per week for six months; a control group of 50 subjects did the same

exercises in their own footwear. The results indicated a significant

(20%) increase from baseline for toe flexor strength in the

experimental group, but no change in the control group. The path of

motion of the MPJ (in degrees of dorsiflexion) decreased by 7% in

those who wore the Nike Free but did not change significantly in the

controls. And a significant 5% increase in flexor hallucis longus

muscle volume was seen in 25 randomly selected subjects from the

experimental group, with increases of 4% and 5% in the abductor

hallucis and tibialis posterior approaching significance. Neither

group demonstrated a significant change in MPJ range of motion.

Neither the German investigators nor Nike's research team have

looked specifically at whether those documented changes translate

into improved performance. But research from the University of

British Columbia presented in June at the annual meeting of the

American College of Sports Medicine suggested the shoe could be

useful for rehabilitation following an ankle sprain (see " Nike's

barefoot-like Free shoe could play role in rehabilitation, " August,

page 59).

" The hope is that a stronger, more flexible foot in a traditional

running product will perform better and have less risk of injury, "

Pisciotta said. " We have not really tried to follow that up, but we

do get a lot of positive feedback. "

Unstable mates

Like the Nike Free, the Masai Barefoot Technology concept challenges

the small muscles of the foot to work harder by providing less

stabilization. In this case, the minimalist design of the Nike Free

is replaced by a thick rocker bottom sole with a negative heel,

providing the same type of instability while standing as a wobble

board. In fact, standing in the MBT shoe is likely more beneficial

than walking or running in it, Nigg said.

" When you walk or run in the MBT shoe, you have slightly less muscle

activity. It's like riding a bicycle; the faster you ride, the more

stable you are, " Nigg said. " Since you stand a lot during the day,

that's a training effect that can be quite substantial. "

An eight-subject study published by Nigg and colleagues in the

January 2006 issue of Clinical Biomechanics confirmed that center of

pressure excursion was greater in the MBT shoe than in a control

shoe and that EMG activity increased in all tested muscles,

particularly the tibialis anterior. A prospective study (submitted

for publication) confirmed that balance time more than doubled after

six weeks of wearing the shoes.

Looking at effects of the MBT shoe during gait, Swiss researchers

found that subjects took smaller steps than in traditional shoes and

demonstrated EMG increases in the tibialis anterior during swing

phase, the gastrocnemius muscles from terminal swing to midstance,

the vastus medialis and lateralis muscles from midstance to toe-off,

and the rectus femoris muscle in midstance. The study, published in

the September issue of Clinical Biomechanics, also found increased

ankle dorsiflexion at initial contact, a continuous plantar flexion

moment throughout stance phase, and increased knee flexion.

And, consistent with the Chicago study that found benefits of

barefoot walking for patients with knee OA, Nigg and colleagues

reported in the October issue of MSSE that knee OA patients

randomized to wear MBT shoes had greater pain reductions between

three and six weeks than did those who wore control shoes; both

groups experienced significant pain reductions over the 12-week

study period.

Like going barefoot, shoes that mimic the barefoot experience are

not for everybody. For one thing, they're not cheap: the Nike Free

runs about $100, the MBT shoe more than $200. Both Pisciotta and

Nigg noted that similar benefits could be achieved less expensively

by simply running barefoot on sand or standing on a wobble board.

And conditions such as ankle instability, metatarsalgia, or diabetic

neuropathy are likely contraindications to both shoes.

" I would be concerned about the use of the MBT shoe in patients who

had limited triceps surae length or who had equinus foot, " said

T. Gross, PT, PhD, professor of physical therapy at the

University of North Carolina in Chapel Hill. " This would especially

be a concern in an older individual who then might be predisposed to

falling backwards with the negative heel configuration during the

early part of stance phase of walking gait. If a tight triceps surae

were a contributor to a patient's plantar fasciitis, that might be

another reason to stay away from this shoe. "

Irene , PT, PhD, professor of physical therapy and director of

the Running Injury Clinic at the University of Delaware, said she

would generally not recommend the Nike Free shoe for patients with

plantar fasciitis, high arches, or severely pronated feet. However,

she said, one of her patients who had plantar fasciitis and flat

feet went ahead and bought a pair for himself, and to her surprise

the plantar fasciitis symptoms abated and the patient was able to

run short distances in the shoes.

" This is how we often learn things, when patients don't listen to

us, " said , who added that reading up on barefoot running

studies has motivated her to incorporate more barefoot walking in

her own life. " I think perhaps the widespread plantar fasciitis in

this country is partly due to the fact that we really don't allow

the muscles in our feet to do what they are designed to do. "