By: Kirk M. Herring,
DPM, MS, FACFAOM
Fellow, American Academy Podiatric Sports Medicine
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.