Exploratory logistic regression modeling showed that the stage of race was the best predictor of treatment success [odds ratio (OR), 74.9, P ≤ 0.01, 95% CI, 4.7-3277.7], followed by time spent racing (OR, 0.66, P = 0.01, 95% CI, 0.5-0.9) (Figure 4) and opposite dominant handedness (relative to which foot was taped) (OR, 3.7, P = 0.05, 95% CI, 1.1-15.2). Variables that were not statistically associated with treatment success included height, age, sex, weight, pack weight, body mass index (BMI), and race performance.
Multiple linear regression and analysis of variance were used to test correlation between the number of blisters and BMI, performance, pack weight, age, and race stage. Stage of race was most strongly correlated (P < 0.01, R2 = 0.17). Normalizing for time spent racing, analysis of variance of the number of blisters per hour shows the strongest relationship for race location (P < 0.01, R2 = 0.19) and whether tape was reapplied (P < 0.01, R2 = 0.07). Factors that did not have a significant association with the number of blisters included age, weight, sex, BMI, use of Injinji socks (San Diego, CA), and pack weight.
We found that paper tape had a robust protective effect on blister formation on runners' feet in multistage ultramarathons. Paper tape is an inexpensive, readily available, and easy-to-apply intervention that prevented blisters in approximately 3-quarters of the people who applied it. This study was the first to show that a simple adhesive tape can prevent foot blisters.
Blisters may lead to pain and inability to complete a race, with 6% to 16% of nonfinishers of ultraendurance events citing blisters as the primary reason for withdrawing.7,13 These rates of nonfinishers due to blisters may be an underestimation because the pain associated with blisters may lead to a modified gait, which can exacerbate underlying injuries.5,29 Runners citing sprains or muscle injuries as reasons for withdrawal may in fact have blisters that are worsening these injuries. Military trainees with blisters were found to have a higher incidence of overuse injuries, particularly to their knees and ankles,17,19 and those with blisters were 50% more likely to experience additional injuries.21
Prospective studies on blister reduction often examined strategies to decrease friction between the skin and other objects,21,23,30 because the magnitude of the Ff is the major factor found to contribute to blister formation.24 Despite over 40 years of clinical trials on blisters, multiple interventions have not provided a solution to this “enemy of the feet.” Petroleum jelly was found to increase friction and subsequent blister formation an hour after application.24 Application of an emollient combined with antiperspirant was not shown to reduce blister incidence,31 another attempt with antiperspirant alone was more successful,15 but the excessive irritation in the majority of study subjects has discouraged use except in cases of hyperhidrosis.15,32,33 A comparison of common blister prevention bandages (eg, Band-Aid, Moleskin, New-Skin, Compeed, Tegaderm) and a proprietary adhesive bandage Blist-O-Ban (Seaberg Company Inc, Newport, OR) found the lowest coefficient of friction in the adhesive pad34; however, paper tape was not included for comparison. Paper tape has a lower profile than that of most of these commercially available products, with the added advantage of affordability and ease of application to the toes and intertriginous areas. There was high user satisfaction of paper tape in this study, with 81% of compliant study participants who “agreed” or “strongly agreed” (on a 5-point Likert scale) to use paper tape for blister prevention in the future.
Previous ultramarathon studies have found that the most common location for blisters is the toes, accounting for 52% to 65% of encountered blisters.5,6 This locational trend was confirmed in this study with toes representing 56% of pretaped areas, and 50% of blisters occurring on the toes. Increased blister rates on the toes may be due to the greater contact time of this area of the plantar surface, with blister-prone individuals found to have significantly increased pressure and magnitudes of shear stress.35 Paper tape is uniquely suited to protect these blister-prone areas as its soft surface minimizes abrasion and friction blister development to the neighboring toes.36
Contrary to the findings of our smaller previous study,6 there was no correlation with blisters and Injinji socks, likely because those who wore these toe-separated socks did not get blisters at that location, so chose not to directly apply paper tape to the toes. Injinji socks are popular among ultraendurance runners, used by 45% (n = 49) of our compliant study participants Although we did not see significant correlation with toe blisters and Injinjis, it seems reasonable to avoid the use of paper tape on the toes with Injinji socks.
Feet of ultramarathon runners are exposed to heat, moisture, and repetitive activity for extended periods of time. The number of times a frictional stress is applied has been shown to increase blister rates.24 By analysis of IDR, we found that those who developed a blister under the tape (treatment failure) encountered it early in the race, whereas those who had treatment success had blisters developing appreciably later in the race in the noncovered locations. Figure 4 supports the efficacy of paper tape for blister prevention. This intervention likely minimized the shear stress at the blister vulnerable areas, as these areas have been found to have a 50% increase in shear time integral values compared with nonblistered sites.35
Of the compliant participants, there were 47 people (43%) who reapplied tape a total of 121 times. The need for tape reapplication was associated with an increased number of blisters, although not with treatment success or failure. It stands to reason that race locations (such as Madagascar and the Gobi) with wetter courses may have led to treatment failure by poor tape adhesion as seen by the lowest success rates. These wet conditions are also more apt to contribute to increased blister formation, represented by the greater number of blisters encountered. Repetitive rubbing on moist skin produces higher Ff than on dry or very wet skin.21,23,27 Wetter environments likely increased the need for frequent reapplications, possibly minimizing the overall benefit of paper tape. Although the most common reason for protocol noncompliance was the lack of tape adhesion, there is a benefit of the weak adhesive qualities of paper tape in that it minimizes the possibility of unroofing a blister upon its removal. The intact superficial epidermal cells of the stratum corneum and stratum granulosum form the blister's “roof.” In blister prevention and treatment, the maintenance of the roof's integrity optimizes healing rates,28 which highlights the utility of paper tape for dermatologic maintenance.
There are multiple variables at play over a 155-mile 6-stage ultramarathon that may have an effect on blister incidence and the success of a prophylactic. There was wide variation in treatment success between the study sites, which may be a reflection of these factors, but interrace conclusions are limited by combination of the cohort for study power. Interrace data were combined for the analysis as each race had similar design, length, and logistical demands; as the environmental and race conditions varied between the study locations, this assumption may have led to disparate results. However, our cohort grouping was similar to multiple studies that have combined athletes from different races for analysis.6,8,38
The Pre-TAPED II study methodology examined the areas at highest risk for blister development unique to each runner on 1 randomly assigned foot. The study participants directed 92% of the taped areas. Although the larger surface area of the foot that was untaped may have biased the results toward a positive study outcome, the historical predilection of blister development in these taped areas offered greatest protection and thus provided us maximal insight into intervention efficacy.39
Participants were not blinded to outcomes, as the end-of-study data collection was by self-reported questionnaire. This was logistically unavoidable. Although all study participants were requested to avoid taping the study foot, we could not standardize other foot care interventions that could possibly have led to unknown variables affecting outcomes.
We demonstrated than an inexpensive and easy-to-apply adhesive tape prevented foot blisters in runners. Foot care represents a substantial burden on medical teams at these races, and blisters cause significant discomfort to athletes, which may negatively impact race performance. This simple pretaping technique of blister-sensitive areas may substantially improve utilization and enjoyment of the outdoors by minimizing both the number and occurrence of friction foot blisters.
The authors gratefully acknowledge Mary Gadams and RacingThePlanet staff for their support of scientific research and the athletes whose participation and enthusiasm for endurance running made this study possible.
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Keywords:Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.
blisters; feet; ultramarathon; runners; injury prevention; paper tape