- The basis of injury risk lies within the balance of
intrinsic and extrinsic control. Intrinsic factors rep-
resent each specific athlete’s alignment, stability,
flexibility, and imbalances that are unique to him or
her. Extrinsic factors include surfaces, weather,
training programs, and footwear. The intrinsic and
extrinsic factors are dependent variables of each
other. To assess proper footwear selection, the ath-
lete’s intrinsic factors must be assessed to determine
the best functional outcome (O’Connor and Wilder,
2001). - Incorrect footwear choices can exacerbate or cause
lower extremity dysfunction, while ideal footwear can
help in prevention or even speed healing caused by
decreased tissue stress on impaired structures
(Stacoff, Kalin, and Stussi, 1991; Nigg et al, 2003;
Wakeling, Pascual, and Nigg, 2002; Roberts and
Gordon, 2001; Hennig and Milani, 2001; Barnes and
Smith, 1994). - Different shoe constructions in the same runner result
in significant differences in peak pressures distribu-
tion measured both in and outside the shoe (Sharkey
et al, 1995). - The goal of any shoe/foot interface is to provide cush-
ioning and increase functional stability about the
foot’s tri-planar motions of pronation and supination
throughout the stance phase of gait and provide proper
support for the propulsion phase of the gait cycle
(Barnes and Smith, 1994).
SHOE CONSTRUCTION AND ANATOMY
- Upper:Functional unit is the heel counter. This is a
plastic molding that wraps around the heel to control
pronation at heal strike. Achilles tab cut-out in the rear
of the shoe is made to decrease friction on the Achilles
complex. The upper is usually made of highly breath-
able fabric to minimize heat build up. This may be
reinforced by Gore-Tex or similar fabric for water
resistance. - Lacing:Round laces slide through holes in the upper
more easily than flat laces and reduce pressure points
in the dorsum of the foot. Various lacing techniques
are available to minimize pressure or increase stabil-
ity and tension on the foot. - Midsole:Functional part of the shoe. The midsole is
usually made up of a mixture of EVA and polyurethane.
EVA has the advantage of being light in weight and
available in multiple densities so that the manufacturer
can manipulate the amount of support for a given shoe
type. Polyurethane is heavier, but is longer lasting.
Most shoes use a combination of the two to achieve the
desired balance between weight and cushioning. Most
shoe companies have developed a trademark insert
such as Air, Gel, Grid, Hydroflow, Torsion, Rollerbar,
and Adeprene. The goal of these is to increase cushion-
ing, dissipate stress forces, and increase durability,
while keeping weight low. Most companies have rein-
forced areas around the inserts to increase stability
where needed.- Lastings:The lasting sits on top of the midsole and is
glued or stitched depending on the control require-
ments. The following are types of lastings: Board-
favors motion control. Slip or California-favors
cushion and flexibility. Combination-board last rear-
foot, and slip last in the forefoot. - Insole or Sockliner:Usually a thin layer of cushion
material, mostly to smooth the surface of the foot. The
insole does not provide any functional stability to the
shoe and usually breaks down in its cushioning prop-
erties with 1–2 weeks. This should be removable for
replacement with over-the-counter insert or custom
orthoses. - Outsole:Most current shoe models are a mixture of
carbon rubber for firm support and durability, and
softer blown rubber for increased cushioning. Some
manufactures utilize a flare in the heel. This can help
to increase stability in the rear foot but can also
increase the torque moving torsionally through the
foot and increase pronation. - Last or shape:This is different from the lasting and
is not a separate component of the shoe, but the design
element on which the shoe is built. A curved last will
encourage pronation, a straight last will provide addi-
tional stability, and a semicurved will provide ele-
ments of both. (see Table 72-1)
ANATOMICAL DETERMINANTS- The selection of footwear for the athlete needs to be
based on a comprehensive foot and lower quarter
assessment to recommend the proper balance of con-
trol versus cushion (Frey, 1997).
438 SECTION 5 • PRINCIPLES OF REHABILITATION
TABLE 72-1 Three Major Running Shoe Categories
SHOCK MOTION
ABSORBTION STABILITY CONTROL
Slip or California lasting Combination lasting Board lasting
Soft midsole Medium density midsole Firm midsole
Curve last Semi curved last Straight last
Blown rubber Mix (blown and Carbon rubber
carbon rubber)