Morphological Changes and MRI Characteristics of the Achilles Tendon in Amateur Marathon Runners With Different Running Experience

BACKGROUND: With the escalating popularity of marathon running, Achilles tendon injuries, particularly gradual-onset Achilles tendon injury, have become common, often causing substantial training disruptions. However, the influence of running experience on the Achilles tendon structure in amateur runners remains largely unclear. This study aimed to investigate the association between running experience and asymptomatic Achilles tendon pathology as well as its structural changes. METHODS: This was a cross-sectional observational study. Forty-eight amateur marathon runners were categorized into four groups based on running experience (1, 3, 5, and > 5 years), with 12 healthy nonrunners as controls. Inclusion and exclusion criteria were strictly applied. All participants underwent MRI scanning using a 3.0 T GE scanner. Two radiologists evaluated MRI scans for pathology and measured tendon length, thickness, volume, and cross-sectional area (CSA). Statistical analyses, including Shapiro-Wilk, ANOVA, Kruskal-Wallis H, and chi-squared tests, were conducted using SPSS 23.0. RESULTS: Baseline characteristics showed no significant group differences. Qualitative analysis revealed that the prevalence of midportion tendinopathy, insertional tendinopathy, and retrocalcaneal bursitis increased significantly with longer running experience. Quantitative measurements indicated that tendon thickness, volume, and CSA were significantly greater in long-running groups compared to short-running and control groups, whereas tendon length remained unchanged. Interobserver reliability was excellent. CONCLUSION: In amateur marathon runners, running experience is associated with increased asymptomatic Achilles tendon pathology and morphological remodeling. Prolonged running may induce both adaptive and degenerative changes, highlighting the importance of MRI-based monitoring for early intervention in high-risk populations.