As
the push-off phase of running is approached, the foot supinates in order to
become a rigid lever and propel the body forward, So in essence, the foot
initially coils to absorb the body’s weight then recoils to propel the body
onto the other foot(15).
Thus,
if the foot rolls in excessively, the subject is a pronator. Pronators tend to
roll medially throughout the lower extremity during the stance phase. They also
tend to have a more supple, shock absorbing foot. The drawback to this type of
foot is that more power will be necessary during push off. When looking at old
shoes of a pronator they deform medially. The medial arch of the midsole is
compressed, and there is extensive wear at the lateral aspect of the heel and at
the medial forefoot. The pronator may also have low arches. Therefore, while
it is important for the foot to have good shock absorption, athletes with
pronated feet also need shoes which emphasize control of the rear foot.
Research
has shown that shoes constructed with soft materials in the soles and uppers,
or shoes that are broken down on the medial aspect, may allow a medial roll of
the foot and ankle during stance(16). Clarke, and coworkers(17), noted that
shoes with a soft midsole and no heel flare allow the greatest amount of
pronation, while shoes with hard midsoles and a 30 degree flare allowed the
least pronation.
Supination
is on the opposite end of the spectrum from pronation. If the foot rolls out
excessively, the subject is a supinator. Supinating feet do not absorb shock
well, and their shoes should provide adequate cushioning for the lateral edge of
the foot. Tell-tale signs of shoe wear in a supinator include old shoes that
tilt laterally, laterally compressed midsoles, and soles that are overly worn
along the lateral edges. Supinators usually have high arches.
Thus,
selecting a running shoe that will adequately support a runner’s lower limb
anatomy and biomechanics can be quite complex, as documented in several
sources(18,19).
The
way people run varies considerably, and a shoe that’s right for one person can
cause another blisters, musculoskeletal strains, or joint
inflammation.
Twenty years ago, the only criteria for buying sneakers was ensuring that the
toes didn’t jam against the end of the toe box. Today, however, shoe design
has become sophisticated with a wide variety of choices available. It has become
necessary for physical therapists, and other health care specialists, to
assess foot biomechanics and running style in order to provide the patient with
helpful information in choosing the correct shoe.
It
is important to determine if a patient is a pronator or a supinator. This can be
done by drawing a line bisecting the Achilles tendon and the calcaneus's. The
alignment of these marks is evaluated with the patient standing. If the
calcaneal line tilts medially then the foot has a tendency to pronate.
Conversely, if the calcaneal line tilts laterally then the foot has a tendency
to supinate(20).
Another
clinical technique used to determine foot posture is to palpate the talar
dome. This is done with the patient standing. If the talus is more palpable
medially, then the foot is in a pronated position. If the lateral aspect of the
talus is more palpable, the foot is in a supinated position.
Wear
of Shoes
A running shoe, when placed on a flat level surface, should not be biased medially or laterally. The main purpose of the shoe is to hold the foot stable. It should be constructed so its upper, midsole and outsole are firmly attached (Figure 1). The uppers, heel counter and the sole should be straight. The shoes should not rock from side to side and the shock absorbing pockets should resist collapsing under load. Defective or worn out shoes which don’t hold feet in a neutral position may accentuate a preexisting musculoskeletal imbalance (i.e. excessive pronation or supination). This may lead to unnecessary aches and pains and, if not treated, a more serious or permanent injury.
The
importance of carefully inspecting running shoes for manufacturer’s
defects before purchase, and regular checks for uneven or
excessive
wear throughout the life of the shoe can not be overemphasized. The following
guidelines will help the athlete avoid buying defective running shoes and
max’ prevent unnecessary injuries.
The
shoe should be glued together secure-lv. Test this by holding the shoe and
trying to pull the upper part of the shoe away from the midsole, and the
midsole from the outsole (Figure 2). Any separation will weaken the shoe’s
support.
The
upper part of the shoe should he glued straight into the sole. Test this by
putting the shoe on a level surface and inspect the hack
of the shoe (Figure 3A). The heel counter should appear even, and
should not lean to the right (Figure 3B) or left, A brand new shoe that leans
medially or laterally could cause injury. especially if there is a large asymmetry~ between each shoe of a pair.
The
sole of the shoe should be level to the surface on which the shoe is resting.
Test this b~’ checking that the medial and lateral aspect of the heel is
even when resting on a flat,
level surface (Figure 4Aand B). Compare each shoe individually,
then compare the right to the left shoe for symmetry. An asymmetry of two
millimeters can tilt the shoe in or out significantly.
Test
for asymmetry by applying a downward medial and a downward lateral force to
Figure 3: A) The medial (a) and lateral (b) vertical distances are equal on the left shoe,
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