A new protocol for the biomechanical evaluation of sport shoes and insoles: Comparison between in-shoe prefabricated and off-the-shelf insoles with metatarsal bar

Introduction: Practicing sport is a good habit to control body weight and to maintain a healthy cardiovascular system. However, the importance of wearing the correct sport shoes is underestimated and the choice of footwear is often merely dictated by fashion. However, only few studies have thus far reported the baropodometric effects of different foot types in sport shoes [1], and the influence of different insoles and shoes in running [2]. In this study, an ad-hoc “sport trial” was designed in order to reproduce in laboratory motor tasks common to different sports. Native insoles, i.e. provided with the shoes, were compared to an off-the-shelf sport insole and to a featureless flat insole. Methods: 20 young physically active subjects (10 M, 10 F; age 32±9 years; BMI 22.3±2.8 kg/m2) were asked to perform a series of tasks in an ad-hoc “sport-trial”, in the following sequence: normal walking; fast walking; running; sprints with change of direction; stair ascending; jump off a 0.5mhigh platform; jump on the spot, and side-to-side shuttle run. Three insoles were tested: the prefabricated insoles within the sport shoes (NATIVE); a flat insole in latex (FLAT), and off-the-shelf sport insole (OTS-sport) in EVA featuring a latex heel insert and a metatarsal pad. The testing order of the insoles was randomized for each subject and the test was blind. A capacitive 99-sensor insole system (Pedar, Novel) was used to measure plantar pressure in a number of foot regions. Analysis of the pedobarographic parameters, e.g. peak pressure (PP, kPa) and pressure-time integral (PTI, kPa*s), and statistical analysis were performed using a proprietary software written in Matlab (MathWorks, Inc.). A VAS questionnaire was filled after each test to score the comfort of each insole [3]. Non-parametric paired Friedman test with Bonferroni correction was used to assess statistical differences in pedobarographic parameters and comfort between the three insoles (˛= 0.05). Results: Statistically significant differences in comfort were found between OTS-sport and the other two insoles (NATIVE = 7.0±2.3; FLAT = 7.5±2.3; OTS = 4.2±2.6; p < 0.05). Significant differences in pedobarographic parameters at the same plantar region were observed between tasks, and between the three insoles for the same task. Side-to-side run showed plantar loading mainly at the forefoot (Fig. 1). In fast walking, the OTS-sport showed larger PP and PTI at the rearfoot than NATIVE (PP (kPa): NATIVE = 280±90; FLAT = 302±81, OTS = 328±78; p < 0.05) but no significant differences at forefoot. In running, the OTS-sport showed the largest PTI and PP at forefoot (PTI (kPa*s): NATIVE = 50±19; FLAT = 47±13; OTS = 53±11; p < 0.05). Discussion: In this study, an ad-hoc sport-trial was designed and proposed to allow the acquisition of in-shoe plantar pressure during motor tasks common to several sports. The presence of a metatarsal pad in the OTS-sport insole appeared to affect negatively the insole performance. This study has allowed to get an insight into the effects of foot orthotics on plantar pressure magnitude and distribution in sport shoes, and to measure the forces acting on the foot in different motor tasks in order to help with the selection of the most appropriate combination of footwear and orthotics for each sport.