Abstract: BACKGROUND: Medial tibial stress syndrome is a common chronic lower limb injury among runners, potentially linked to the “muscle traction theory.” However, this hypothesis has not been fully confirmed. 
OBJECTIVE: To investigate whether the contraction characteristics of the soleus, posterior tibialis, and flexor digitorum longus muscles during running are correlated with stress levels at the medial tibial border and influence the occurrence and development of medial tibial stress syndrome using musculoskeletal simulation systems and finite element analysis. 
METHODS: Motion capture data of six subjects running at different speeds were input into the Anybody Modeling System for inverse dynamic simulations during the stance phase at running speeds of 2.5, 3.5, and 4.5 m/s. The calculated boundary conditions were combined with finite element models to examine the stress distribution on the medial tibia. Partial least squares regression was used to analyze the correlation between independent variables (muscle force and elastic potential energy) and the dependent variable (tibial stress). 
RESULTS AND CONCLUSION: (1) There were statistically significant differences in tibial stress levels across different speeds during the stance phase (1%-50%) (P=0.044, F=3.834, ηp2=0.040). (2) Among the three speeds, the average correlation between soleus muscle force and tibial stress was the highest (r=12.999), followed by the correlation between posterior tibialis muscle force and tibial stress (r=-10.735), flexor digitorum longus muscle force (r=-9.751), posterior tibialis elastic potential energy (r=8.012), soleus elastic potential energy (r=9.076), and flexor digitorum longus elastic potential energy (r=-4.782). (3) The results indicate that with increasing running speed, tibial stress levels rise. The contraction of the soleus muscle and the release of absorbed elastic potential energy during running have a significant impact on the development of medial tibial stress syndrome, whereas the roles of the posterior tibialis and flexor digitorum longus muscles have been overestimated. Overall, the study supports the hypothesis that the contraction of the soleus muscle plays a crucial role in the development of medial tibial stress syndrome, consistent with the “muscle traction” hypothesis.

Key words: tibial stress syndrome, biomechanical simulation, medial tibial stress syndrome, anybody modeling system, Abaqus, finite element analysis