in Running, Court, and Fitness Shoes
As recently as
thirty-five years ago, athletic shoes consisted of just a few shoes that were
used for a wide variety of athletic events. There were a few tennis and
basketball shoes. There were no shoes marketed specifically as walking shoes.
Aerobics or fitness shoes were nonexistent. Running shoes only amounted to a
few in number.
today's athletic shoe stores, the number of brands and styles of shoes for all
types of sports is staggering. There are shoes made specifically for wrestling,
rock climbing and windsurfing in addition to the more common sports such as
running, basketball, tennis, racquetball, aerobic dance and walking. In the
running shoe market alone, there are nine major shoe manufacturers with each
manufacturer having about five to ten running shoe models within their line.
Even though the increased selection of shoes increases the possibility of
finding just the right shoe for each set of feet, the large selection of models
creates a large degree of confusion among the consumer.
It is actually
this diversity and complexity within athletic shoes that is their most
interesting aspect. Shoes that have different shapes are made of different
materials, and which are put together by different construction methods all
will function on the foot differently. The purpose of this article is to
explain the major structural differences between the three broadest categories
of athletic shoes (i.e. running shoes, court shoes and fitness shoes) so that their
functional differences may be better appreciated.
walking, is considered a straight ahead sport since it involves no sudden stops,
turns or other maneuvers. Most runners land on their heels and then propel off
of their toes. This heel to toe cycle is repeated hundreds and thousands of
times every running session. The major biomechanical differences between
running and walking are that in running there is always one point during
running when both feet are off the ground and also during running the impact
forces which the foot absorbs are at least twice as great as that found in
strike on the outside of the heel, rapidly pronate, stay pronated for a brief
instant and then resupinate as the heel leaves the ground during the push-off
phase of running. [Pronation of the foot is a rolling inward of the ankle in
which the arch flattens. Supination of the foot is a rolling outward of the
ankle in which the arch increases in height.] Due to the large degree of
variation within the population, there are a large number of runners who
pronate excessively during running causing a multitude of running injuries such
as posterior tibial tendinitis, plantar fasciitis and pes anserinus bursitis,
to name a few.
Because of the
increased impact forces and increased excessive pronation seen in running,
running shoes must be designed both to help reduce excessive shock to the body
and also help reduce pronation in the foot (Fig. 1). Unfortunately, the same
shoe design characteristics that are best at helping to control pronation also
tend to lessen the ability of the shoe to cushion the foot. And conversely, any
shoe designed to maximize the cushioning of the foot during running will tend
to have decreased ability in helping to control pronation.
understand how the characteristics of running shoe design affect foot function,
it is important to detail the structural components of the running shoe. Every
shoe is made of two basic parts, the sole and the upper. The sole protects the
foot from the ground and provides a layer of cushion for the foot. The upper
covers the top and sides of the foot to provide a comfortable fit between the
foot and the shoe and to improve stability of the foot on the shoe sole.
In the running
shoe, the sole is made up of two distinct layers, the outersole and the
midsole. The outersole is the part of the sole that contacts the ground. It is
made of a thin layer of relatively hard, abrasion resistant material which
functions to resist wear, provide traction and allow flexibility in the
forefoot for propulsion.
shoes use a rubber compound with a high carbon content in the heel and forefoot
area, which is similar in composition to an automobile tire, so that the
outersole will resist the abrasion that comes from the heel striking the
ground. Running shoe outersoles also are constructed with studs or ridges in
the midfoot and forefoot area to aid traction on soft or slippery surfaces,
such as wet grass or slick pavement. In addition, most running shoe outersoles
also incorporate some form of transverse grooves placed in the area of the
forefoot so that the shoe will be more flexible in the forefoot once the heel
leaves the ground during the push-off phase.
however, is the part of the running shoe that either makes it work well or
makes it work poorly. The midsole is sandwiched between the upper and the
outersole. The upper is glued or bonded to the top surface of the midsole. The
midsole is the most important part of the running shoe because its design and
construction largely determine whether the running shoe will be a shoe which is
good at providing cushioning, good at controlling pronation, good for heavy
runners or good for nothing.
midsoles are designed so that there is thick cushioning under both the heel and
forefoot to help provide cushioning to the heel and forefoot. The total height
of the midsole and outersole under the heel is generally about 1 inch and the
total height of the midsole and outersole under the forefoot is about
5/8". The 3/8" difference of sole thickness between the heel and
forefoot in many running shoes tends to be preferred by most runners and also
reduces the strain on the Achilles tendon, therefore, reducing the likelihood
of Achilles tendinitis.
The midsole may
be constructed of various materials to provide cushioning and pronation
control. The two most common materials used in the construction of running shoe
midsoles is ethyl vinyl acetate (EVA) or polyurethane (PU). EVA is a copolymer
of ethylene and vinyl acetate that has microscopic air bubbles within it that
makes it lightweight and very cushiony. PU also has a microscopic air bubble
structure like EVA but is generally firmer and more resistant to compression
manufacturers use combinations of different densities of EVA and/or PU within
the midsole of the shoe, along with gel packets, air bags, plastic plates and
other exotic materials to provide what they believe is the proper amount of
cushioning and pronation control for the shoe. Many running shoe midsoles have
a firmer midsole material or a hard plate under the medial heel and a softer
midsole material under the lateral heel so that the medial heel resists
compression more than the lateral heel when the heel strikes the ground in
running [Medial is toward the big toe, lateral is toward the little toe]. This
"dynamic varus wedge" effect does effectively help control foot
pronation to some extent. The softest midsole material is generally placed
under the forefoot since most runners find that good forefoot cushioning is a
very desirable feature when running on hard surfaces.
The upper of a
running shoe also incorporates a stiff heel counter that is commonly stiffer
than in other athletic shoes to help control excessive pronation or supination
during running. Most running shoes also incorporate a raised padded
"Achilles tendon protector" within the design of their upper to
supposedly help protect the Achilles tendon. Most runners find that the
"Achilles tendon protector" serves only as a convenient handle by
which to pull their running shoes on with and serves little importance in
protecting the Achilles tendon from injury.
interior of today's running shoes are removable insoles known as sockliners.
Sockliners serve to cushion the foot and provide some arch support. Many sockliners
in more expensive running shoes serve to support the arch of the foot more
effectively than those seen in cheaper shoes. Nearly all sockliners can be
removed easily from the shoes so that custom foot orthoses may be added to the
shoe to replace the sockliner if needed.
important fact about running shoe design is that running shoes make excellent
walking shoes. Since running and walking are both straight-ahead activities,
their basic shoe designs are quite similar. In fact, I recommend running shoes
for my patients who walk for exercise in favor of many walking shoes since
running shoes are lighter, more comfortable and biomechanically more efficient
at helping control excessive foot pronation than the majority of walking shoes.
include tennis, racquetball, basketball, squash, badminton and volleyball.
Because court sports require sudden starts, stops and side to side motions, the
best shoe construction for court sports is much different than that required
for running (Fig. 2). The sudden side-to-side movements seen in court sports
tend to make the foot slide forcefully either in a medial or lateral direction
on the shoe sole. For example, if a tennis player is moving quickly toward the
right and then uses the right foot to come to a complete stop, the foot will
tend to slide laterally on top of the shoe sole. The only thing preventing the
foot from sliding directly laterally off of the shoe sole is the upper of that
shoe. It is because of this necessity for side-to-side stability that court
shoes must be constructed much differently than running shoes.
shoes, court shoes come in all shapes and sizes depending not only on the sport
which the shoe is designed for but also on the manufacturer. Unlike running
shoes in which the upper of the shoe always ends just below the ankle bones
(i.e. a low-cut shoe), the upper of court shoes may extend partially over the
ankle bones to about the ankle joint level (i.e. a mid-cut shoe) or may extend
above the ankle bones completely covering them (i.e. a high-cut or high-top
shoe). Many basketball shoes tend to be made of a higher cut than other court
shoes due to the relatively great frequency of ankle sprains seen with
basketball. All other shoe design parameters being equal, the higher the cut of
the upper of the shoe, the better that shoe will be at preventing ankle
instability during the activity and the heavier that shoe will be.
Since the goal in
a well designed court shoe is to make the upper hold the foot on top of the
sole, the uppers of court shoes are thicker and made of heavier weight
materials than running shoes or fitness shoes. The uppers of court shoes are
constructed of thicker leathers or synthetic leathers than either running or
fitness shoes. Lightweight and thin materials such as nylon are used less
frequently in court shoe uppers. In addition, many tennis shoes may have an
extra layer of synthetic or natural leather toe box reinforcement to prevent
the upper from wearing through in the toe box area from the scuffing which
occurs during tennis serves.
Many court shoes
also are constructed with an extended outersole or a midsole which rises up on
the sides to the bottom edge of the upper to give added strength to the
sole/upper interface. As a result of the use of thicker upper materials and the
side reinforcement of the sole up onto the upper, court shoes are nearly always
heavier than the same size of running shoe.
The outersole of
court shoes are usually made of a non-marking rubber compound for traction on
outdoor or indoor courts. Court shoes have a much lower profile of tread
patterns on their outersoles than running shoes since court sports are nearly
always played on a dry, flat and smooth surface. In addition, court shoes often
have a circular designs constructed into the outersole under the forefoot area
of the sole to act as a "pivot point" for the shoe during rotational
motions of the foot on the playing surface.
shoes, court shoe midsoles are predominantly made of either EVA or PU. However,
the midsoles of court shoes are firmer and thinner than running shoes to reduce
the instability of the court shoe during side-to-side movements. Shoes with firmer
soles have better side-to-side stability since the force of body weight through
the foot will not deform a firm sole as much compared to a cushiony sole. The
more that a shoe sole deforms under the forces which the foot exert on it
during aggressive maneuvers, the more likely the shoe sole will tilt to one
side or the other which may lead to either pronation or supination instability
at the ankle joint complex.
increase the height of the foot and ankle from the ground that, in turn, increases
the distance of the ankle joint complex from the ground. The higher that the
ankle joint complex is from the ground, the longer is the lever arm for the
reaction force from the ground to cause either a pronation or supination force
on the foot and ankle. Therefore, the thinner soles of court shoes decrease the
likelihood of ankle sprains since the ground has a much shorter lever arm to
produce pronation or supination forces on the ankle joint complex.
About fifteen to
twenty years ago there was a dramatic increase in the popularity of aerobic
dance. At that time, the shoes worn for aerobic dance were either running or
court shoes. Unfortunately, since running and court shoes were not specifically
designed for the demands of aerobic dance, many injuries occurred. Those
aerobic dancers wearing running shoes had good cushion to the forefoot, but
suffered from ankle sprains due to the lack of lateral stability in running
shoes. Those dancers wearing court shoes had good side-to-side stability, but
suffered from painful symptoms in the forefoot due to the lack of cushioning in
the forefoot in court shoes.
manufacturers responded with the aerobics shoe that blended technologies from
both the running shoe and court shoe. The result was a shoe with a midsole
thickness and degree of cushioning midway between that of court shoes and
running shoes. In addition, the aerobics shoe had an upper that was midway
between the court and running shoe in material weight and thickness.
Today, shoes made
for aerobic dance are very similar in design to those shoes made for the
various activities available in a health or fitness club. Therefore, shoes made
for aerobic dance and cross-training are now known as "fitness
shoes". Understanding the construction of fitness shoes is important since
they not only are a very popular style of shoe, but their relatively recent
birth into the shoe marketplace demonstrates the ability of shoe manufacturers
to design a totally new and unique style of shoe to meet the biomechanical
demands of a new sport (Fig. 3).
The fitness shoe
has been designed using technological features from both running shoes and
court shoes to create a shoe that is actually a better all-purpose shoe than
either the court shoe or the running shoe. It is lighter in weight and more
well-cushioned than the court shoe and much more able to resist side to side
movements of the foot than a running shoe.
The upper of fitness
shoes can range from a low-cut to a high-cut with the most popular height being
a mid-cut. The mid-cut upper is a very popular style in fitness shoes since it
does provide extra lateral stability without adding a great deal of extra
weight to the shoe. The fitness shoe upper is made from a combination of
thinner natural or synthetic leather and nylon that decreases the weight of the
shoe compared to a court shoe. However, since the fitness shoe upper is more
substantial than the upper found in running shoes, the lateral stability of the
fitness shoe is greater than in the running shoe.
Like court shoes,
many fitness shoes use an extended outersole or midsole on the medial and
lateral sides of the upper to provide extra bonding strength to the sole/upper
junction. The extended midsole is now very popular in fitness shoes and does
provide an extra degree of lateral stability to the shoe.
The outersole of
fitness shoes are very similar to court shoes being made from non-marking
rubber compounds in a low profile. However, the midsole in a fitness shoe is
thicker than that seen in the court shoe to provide extra cushioning to the
forefoot and rearfoot during aerobic dance, running and other impact
activities. Even though the midsole in a fitness shoe is not as thick as that
in running shoes, the fitness shoe can safely have a thicker midsole in its
design since the side to side activities seen in fitness shoes are not as
aggressive as that seen in court sports.
Certainly in the
case of all the shoes described, it is clear that the structure of the shoe
determines how the shoe will affect the function of the foot within that shoe.
Whether it is the composition of the outersole, midsole or upper, or it is how
the sole is attached to the upper, or it is any other shoe design parameter,
the construction of athletic shoes must match the biomechanical requirements of
the specific athletic activity in order for the shoe to be useful and desirable
for the athlete.