An Elastic Foot Orthosis for Limiting the Increase of Shear Modulus of Lower Leg Muscles after a Running Task: A Randomized Crossover Trial

Background: Excessive foot pronation may be attributed to an increasing burden on leg muscles during running, which might be a factor in medial tibial stress syndrome. We developed an elastic foot orthosis (EFO) that can decrease foot pronation and aimed to identify whether this orthosis could limit the increase in lower leg muscle hardness after running. Methods: Twenty-one healthy volunteers participated in this randomized crossover trial with an elastic or sham foot orthosis (SFO). All volunteers ran on a treadmill for 60 min while wearing either orthosis. Muscle hardness of the posterior lower leg was assessed using shear wave elastography before and after running. The Wilcoxon signed rank test was used to compare muscle hardness between the two orthotic conditions. Results: No significant differences were observed between the two orthotic conditions before running (p > 0.05). After running, the flexor digitorum longus (FDL) hardness in the EFO group was significantly lower than that in the SFO group (p < 0.01). No significant changes were observed in the other muscles. Conclusion: The results suggest that the EFO can restrict the increase in FDL hardness with running. The EFO may be an effective orthotic treatment for medial tibial stress syndrome.