Functional Evaluation of a Shock Absorbing Insole During Military Training in a Group of Soldiers: A Pilot Study

Abstract

Objective Soldiers’ lower limbs and feet are frequently affected by overload- and overuse-related injuries. In order to prevent or limit the incidence of these injuries, the use of foot orthoses is often recommended. The aim of this study is to assess the effects of shock-absorbing insoles on in-shoe plantar pressure magnitude and distribution in a group of professional infantry soldiers wearing military boots during standard indoor military training. Methods Twenty male professional soldiers of the Italian Army (age 35.1 ± 6.1 years; BMI 25.2 ± 2.3 kg/m2) were recruited for this study. Each subject underwent clinical examination to assess possible overuse-related diseases of the lower limb and trunk. Subjects with altered foot morphology according to the Foot Posture Index (FPI) were excluded from this study. Twelve subjects were considered eligible and therefore underwent an indoor training routine comprised of marching, running, jumping inside parallel bars and jumping from different heights. Soldiers repeated the training session twice wearing standard military boots along with two types of insoles: the standard prefabricated insole within the boots (STI), and a special shock-absorbing insole (SAI) featuring an elastic medial arch support. A 99-capacitive sensor insole system was used to record plantar pressure distribution in both feet. Analysis of in-shoe pressure parameters at rearfoot, midfoot and forefoot and in the total foot was performed via a custom-software application developed in MATLAB. Perceived foot comfort (VAS 0–15) was also assessed. Results Pressure parameters recorded during walking and running were considered suitable for statistical analysis. In the whole foot region, pressure parameters were 18–22% lower in military boots fitted with the SAI during walking and 14–18% lower during running. SAI resulted in better comfort (+25%) with respect to the prefabricated boot orthotics (median comfort: SAI = 15/15; STI = 12/15; p = 0.0039) both during walking and running. Conclusions Shock-absorbing insoles can be an effective solution when fitted inside military boots. The present functional evaluation shows that wearing a prefabricated shock-absorbing insole can provide a significant amelioration of perceived foot comfort and plantar pressure parameters. Further studies are now needed with a larger population and more demanding exercises.

Footwear comfort: a systematic search and narrative synthesis of the literature

“…The anchor statements indicating the lowest possible comfort score included ‘not comfortable at all’ [19–22, 25, 26, 30, 39, 49, 50, 53, 55, 56, 61–65, 73, 79, 82–85, 89, 93], ‘very uncomfortable’ [27, 28, 40, 41, 45, 46, 58, 68, 74, 78, 79, 98], ‘least comfortable’ [44, 76, 80, 90], ‘extremely uncomfortable’ [48, 59, 89], ‘not comfortable’ [71, 75], ‘not at all comfortable’ [15, 18], ‘not acceptable’ [37, 70], ‘totally disagree’ [10], ‘least comfortable imaginable’ [35], ‘not satisfactory’ [42], ‘very bad comfort’ [43], ‘very, very low’ [47], ‘minimum comfort’ [69], ‘maximal pain/discomfort’ [99], ‘not very comfortable’ [100], ‘completely uncomfortable’ [104], ‘extremely bad’ [57] and ‘unbearable discomfort’ [87]. The anchor statements indicating the highest possible comfort score included ‘most comfortable imaginable’ [19–22, 25, …”

“…Studies comparing different insole designs have generally found that softer, more flexible insoles are perceived as more comfortable (in casual footwear [99], running shoes [31, 67, 80] and military footwear [42, 69]). However, comfort perceptions related to insole hardness may vary according to an individual's occupation, as Anderson et al [14] have reported that people standing for long periods at work prefer soft materials under the heel and forefoot but firmer materials under the arch.…”

“…A wide range of measurement tools have been used to quantify comfort, including simple dichotomous responses [11,12,29,94], ranking footwear conditions in order of preference [14, 31-33, 36, 47, 48, 52, 60, 63-65, 76, 77, 79, 81], 4-point [42,80], 5-point [37,40,45,58,70,76,97], 6-point [59], 7-point [47,64,79,87], 9-point [57] and 12-point [41] Likert scales, 10-point numerical rating scales [43,78], and 100 mm [15, 16, 18-21, 27, 28, 30, 35, 39, 48, 49, 53, 56, 63-65, 67, 68, 71, 73, 74, 77, 79, 82, 85, 89, 90, 93, 99, 104, 105], 150 mm [22,25,26,36,46,50,55,61,62,66,69,75,83,84,98,100] and 170 mm [44] visual analog scales. The anchor statements indicating the lowest possible comfort score included 'not comfortable at all' [19-22, 25, 26, 30, 39, 49, 50, 53, 55, 56, 61-65, 73, 79, 82-85, 89, 93], 'very uncomfortable' [27,…”

Relationship of footwear comfort, selected size, and lower leg overuse injuries among infantry soldiers

“…Our study results showed that subjects wearing the wrong shoe size reported lower footwear comfort ratings. To potentially increase footwear cushioning and comfort shock-absorbing insoles have been recommended [ 8 , 40 ]. Prefabricated foot orthoses were found to be effective in preventing lower limb overuse injuries [ 41 ].…”

Effects of wearing raised-heel insoles for 60 days on physical functions: focusing on adult males in their twenties

“…Oh et al [5] have argued that people have difficulty walking with the correct posture when the heel height of the shoe is over 5 cm, which fatigues the foot very easily. Insoles were originally designed and developed to achieve a functional objective to prevent muscle fatigue by distributing body weight and protecting the ankle and knee joints by absorbing impact [6]. However, as more people are becoming interested in appearance, young men often use HH shoes and RHIs to overcome dissatisfaction with their heights and gain confidence regarding their heights [1,7].…”