Cross-Country and Track (XCT) athletes` training volume is often dictated by season, eliciting lower body musculoskeletal adaptations; but how these alterations impact seasonal injury risk is unknown. PURPOSE: To evaluate site-specific musculotendinous characteristics using diagnostic ultrasonography and musculoskeletal indices using Dual-energy X-ray Absorptiometry (DXA) in NCAA Division I XCT athletes across competitive seasons. METHODS: XCT athletes (n=23) were assessed pre/post cross-country and post outdoor (n=14) seasons. Voluntary informed consent, injury, training, and NSAID use logs were collected prior to a total body DXA scan with shank region of interest (ROI; tibial plateau to distal foot), for bone and body composition measures. Real-time brightness mode ultrasonography assessed cross-sectional area (CSA), thickness (TH), pennation angle (PA), and subcutaneous fat-corrected echo intensity (EI) for the bilateral gastrocnemii and tibialis anterior coinciding with multi-site TH, CSA, and EI of the Achilles tendon. Repeated Measures ANOVA compared seasonal differences. Cohen`s d effect sizes were calculated and a=0.050. RESULTS: Bilateral musculature CSA, PA, and EI increased pre/post XC (all p=0.001; d:0.48-0.87), coinciding with increased Achilles tendon CSA and TH (all p<0.001; d:0.23-0.88) and reduced EI (all p<0.001; d:0.65-0.87) across all sites. However, all measures returned to near pre-XC levels post-outdoor (all p=0.048; d: 0.24-1.07; Figure 1). Bone indices and body composition remained unchanged all year (all p=0.097; d: 0.01-0.14). CONCLUSION: These data indicate an elevated seasonal Achilles tendon injury risk from increased intramuscular adiposity corresponding with a thicker, less fibrous tendon. Detrimental adaptations coincided with sustained high mileage and NSAID use but subsided concurrently with reduced mileage and drug use; warranting across-season evaluation for precise injury risk assessment.
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