Discussion
AH stiffness, pronation, flatfoot
SECONDARY
The primary purpose of this study was to investigate the effects of various plantar taping methods on midfoot joint and plantar tissue mechanics. We focused on taping methods that could be available for at-home application and compared these tapes with Low Dye, a traditional clinically applied inelastic taping method, as well as a barefoot control. Our hypotheses were mostly upheld, with longitudinally inelastic tapes (LD, FS, and FD) generally reducing arch motion and A/P shear spreading forces and laterally inelastic tapes (LD, FD, and KT) reducing M/L shear spreading forces. Our secondary purpose, investigating the influence of foot posture, was partially upheld, with lower MLA heights showing a greater tape influence.Our primary measurements revolved around the MLA deformation or drop that occurs from initial contact through mid-stance, which has a direct relationship with plantar fascia strain. During these phases, the rearfoot everts about the subtalar joint and the MLA drops in a somewhat coupled mannerThe effect of FS tape on MLA drop (using SHA pronation) was significantly correlated with standing AHI, suggesting a potential relationship between taping effects and foot structure. The correlation between pronation difference and AHI was negative, with lower AHIs (i.e. flatter MLAs) associated with greater taping effects. This may simply be due to a greater potential for manipulating the position of the MLA during tape application in lower arched feet. AH stiffness was close to, but not quite, significant, and may be worthy of future investigation (the correlation was positive, suggesting potentially greater flexibility associated with greater pronation effects). However, the lack of a correlation between AHI and AH stiffness also suggests that these two measurements are capturing slightly different aspects of foot structure. While we only tested healthy participants, the fairly strong relationship with AHI is encouraging given the potential for pathologies/injuries in flatfoot deformityWhile reduced MLA RoM in early and mid-stance is likely beneficial in reducing plantar fascia strain, longitudinally inelastic tape also affects MLA rise in late stance, which could have a mildly detrimental effect on gait energetics. In late stance, MLA rise contributes to propulsive power generationIn addition to MLA motion, we also evaluated the effects of taping on other plantar tissues through our directional shear force metrics. While the relationship between these metrics and taping effectiveness is not as straightforward, they provide some initial insights into the effects of taping on both joint mechanics and plantar skin deformation. In the A/P direction, the greatest spreading forces occur in mid-stance, when the arch is loaded and the forefoot and rearfoot generate opposing actions (much like a loaded truss), thus part of this spreading likely overlaps with the joint RoM results. Indeed, our A/P spreading results closely matched our MLA RoM results, although FD did not quite reach significance compared with barefoot. In the M/L direction, the laterally inelastic FD decreased spreading; however, LD and KT did not. For LD, this is likely due to the tape location, which leaves open the areas under the heel and forefoot where the greatest spreading occursStudy limitations primarily revolved around ecological validity and clinical significance, as our measurements focused on joint and plantar tissue mechanics in healthy participants in a lab based setting. We stopped short of estimating plantar fascia strain itself—this could be done using a simple truss model