How Socks Make The Feet

While typically thought of as a minor nuisance injury, blisters of the feet are
among the most common injury suffered by athletes and can lead to more
serious injuries. A recently published study examining friction blisters among
military personnel discovered that recruits who suffered from friction blisters
also experienced a higher incidence of overuse injuries, including stress
fractures, tendonitis and shin splints. A poll of runners completing a warm
weather marathon found that one out of every five runners had suffered a
friction blister. Blisters have a far greater potential to sideline athletes than
generally is thought possible.
Athletes should choose their footwear and socks carefully. The first defense
against friction blisters is proper fitting socks and shoes. Numerous high tech
sock choices exist, including one which lifts perspiration off the skin like
a “squeegee”, while others wick perspiration, some have anatomically placed
padding to increase cushioning and others utilize two separate layers of fabric
to decrease friction next to the skin.
It is well known that moisture on the skin increases friction, torque and
shearing forces by increasing the adhesion of the skin to the sock. This
increased coefficient-of-friction transfers mechanical stress from the sock to
the deeper layers of the skin where a separation of skin layers may result in
the formation of blisters. Socks made with a new fiber technology
Drymax® “squeegee-up” (http://www.drymaxsocks.com/videos.php)
perspiration produced during exercise and quickly transport this moisture
away from the foot to the sock’s outer layer and then to the upper part of
the shoe where it can evaporate away. To optimize moisture management, it
is best to select socks constructed and knit with synthetic fibers, specifically
intended to carry moisture away from the foot
(http://www.drymaxsocks.com). Synthetic fibers such as Coolmax®, a
polyester fiber (http://www.coolmax.invista.com/), acrylic, nylon,
polypropylene and the natural fiber merino wool are common to many athletic
socks.
Controlling perspiration build up around the foot and dissipating
friction are not necessarily inclusive for technical socks. In fact, three of the
most popular fibers used in the construction of technical socks possess good
moisture management properties but also exhibit higher coefficient-of-
friction. This friction may be minimized by sock designs that include
anatomically padded zones or double layering. Certain models of Drymax®
socks have effectively combined the benefits of moisture management with a
very low coefficient-of-friction PTFE fiber called Profilen®, thus providing for
the design of an effective blister-preventing sock, suitable for diabetics,
tennis players, triathletes and ultra distance runners or athlete’s just prone to
getting blisters.
Friction and torque created during athletic activity generates
shearing forces between the skin and sock / shoe surfaces. These forces
when absorbed by the skin can accumulate, weakening the bonds between
skin cells and lead to the development of a friction blister. Typically, these
forces are below the threshold felt by most athletes until it is too late.
Various sock designs are available to minimize these forces; most common is
the anatomical placement of dense padding to cushion areas of the foot
prone to blisters such as the toes, forefoot and heel. Also popular are double
layer socks which attempt to divert friction away from the skin and shift it
outward between the sock’s two layers. For those individuals who frequently
suffer from blisters between toes anatomical toe socks can minimize the
friction and rubbing between toes that occurs during running. Unfortunately,
toe socks can be awkward to put on and take off and can feel somewhat
unnatural by spreading the toes with two layers of material between each
toe.
Athletes should consider their individual sock needs, including fit,
durability, leg height, cushioning, support, thermal properties and especially
moisture management. Avoid pressure points; select properly fit socks and
carefully inspect any new sock on the inside for potentially injurious sock
seams. When considering the construction of the sock select only socks
made with flat knit toe seams and a Y-heel, or vector heel pocket designs.
Socks, like shoes, are sized to the foot and improper fit can lead to blisters.
Avoid overly tight or loose fit socks. Ill fit socks which are too tight may bind
the toes, while socks which fit too loose can lead to harmful wrinkles, capable
of pinching the skin and causing blisters.
During warm weather the accumulation of heat around the foot has
been considered a contributing factor in the formation of blisters. Many
socks are thinner over the instep and under the arch. Some sock brands
offer ventilation panels under the arch and/or base of the toes to help
dissipate heat generated during athletic activity.
Healthy skin is less likely to develop a friction blister. Athletes
should avoid chronic dehydration especially during warm weather training
and / or during periods of heavier training efforts. Healthy, well hydrated skin
will tolerate more stress before breaking down and developing a friction
blister.
No discussion about socks is complete without some attention to
shoe fit. Proper fit of any new shoe should be done with the preferred sock
thickness, and after training activities, or later in the day after the foot has
swollen. It is also important to carefully inspect new shoes for manufacturing
flaws, check inside the upper and the outside for prominent seams or
stitching, abrupt fabric edges, fabric wrinkles, malformed thermal plastic
parts, misaligned lace eyelets or tongue or excess fabric, all of which could
lead to hot spots or blisters.
When blistering persists and basic steps have been taken to resolve
this problem then seek professional assistance. The Fellows and Associates
of the American Academy of Podiatric Sports Medicine
(http://www.aapsm.org/) are uniquely equipped and dedicated to meet the
needs of the athletic community.
By: Kirk M. Herring, DPM, MS, FACFAOM
Fellow, American Academy Podiatric Sports Medicine
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