Biomechanics of the plantar fascia in running and the implication for plantar fasciitis

Abstract

Running is an inexpensive form of physical exercises and has been gaining popularity in the past decades. However, the growth of the healthy lifestyle is accompanied by an increased risk of running-related injuries, among which plantar fasciitis is one of the preponderances. With the numerous efforts in studying the biomechanics of plantar fascia, researchers intended to minimize the risk of the problems by optimizing exercise paradigms or utilizing taping treatments. Nevertheless, challenges in assessing the loading environment and internal conditions of the plantar fascia impede the understanding of its interaction with these extrinsic factors. Hereinafter, the overall objective of this study was to investigate the internal biomechanical feature and mechanical environment of the plantar fascia that provides more insights for both scientists and runners. The scope of the study included the investigation of 1) biomechanical property of plantar fascia and 2) plantar fascia loading upon different foot strike techniques in running, and 3) the offloading effect of different taping techniques, which were achieved by ultrasound elastography, locomotion analysis, musculoskeletal modeling, and finite element analysis. In the first study, thirty-five recreational runners using different foot strike techniques received the ultrasound elastographic measurements. Forefoot strikers exhibited reduced plantar fascia elasticity compared to rearfoot strikers, which could potentially relate to the pathomechanics of plantar fasciitis. Immediately after, the second study aimed at reconstructing a finite element model of a typical runner and examining the differences in plantar fascia loading between forefoot strike running and rearfoot strike running. The model simulation was driven by data of the locomotion analysis and musculoskeletal modeling of the participant, following the procedures of a mesh convergence test and model validation. The predictions showed that, compared to rearfoot strike, forefoot strike increased the tensile force on the plantar fascia and depressed the medial longitudinal arch. The findings further supported the additional risk of plantar fascia injury contributed by forefoot strike. Using the same model, in the third study, we evaluated two tapping techniques (Fascia taping and Low-Dye taping) and their capabilities to offload the plantar fascia during running. The prediction showed that Fascia taping was more effective in reducing the strain of the fascia band and increasing the arch height, whilst the effects of Low-Dye taping seemed unapparent. In conclusion, we investigated different biomechanical features of the plantar fascia, from intrinsic, extrinsic factor to assistive device (taping). The significance of this study lay in its potential to provide quantitative evidence suggesting risk factors of plantar fascia problems by integrating ultrasonography, gait experiments and computer simulations, otherwise difficult to be assessed using in-vivo experiments alone. Moreover, we overcame some technical challenges in simulating highly dynamic scenarios with deep tissue deformation using a smooth particle hydrodynamics (SPH) technique, which was traditionally used for fluid or astrophysical simulation. Future studies shall consider a detailed material constitutive model of the plantar fascia considering the yielding and micro-torn responses. In addition, a prospective, controlled study can be conducted to confirm the causal relationship between the risk factors and plantar fasciitis.