Achilles tendon adaptation in cross‐country runners across a competitive season

Ultrasound tissue characterization ( UTC ) is an imaging tool used to quantify tendon structural integrity. UTC has quantified Achilles tendon ( AT ) acute response to load in athletes; however, AT response to cumulative load over a season is unknown. The purpose of this study was to evaluate AT response across a four‐month competitive season in collegiate cross‐country ( XC ) runners. Participants (n=21; male=9, female=12; age=19.8±1.2 years; height=171.9±8.9 cm; weight=60.2±8.5 kg) were imaged using the UTC device with a 10‐ MH z linear‐array transducer mounted in a tracking device. The device captures images at 0.2 mm intervals along the AT . UTC algorithms quantified the stability of pixel brightness over every 17 contiguous transverse images into four echo types (I‐ IV ). A total of 168 scans (n=21, bilateral limbs) were performed monthly across the four‐month season (Aug=M1, Sep=M2, Oct=M3, Nov=M4). Echo‐type percentages (%) were calculated from each scan. Generalized estimating equations ( GEE ) linear regression models evaluated echo‐type % change (β) over the season (M1=reference). Type I increased from M1 to M4 (β=9.10, P <.01; 95% CI : 7.01, 11.21) and Type II decreased from M1 to M3 (β=−2.71, P= .018; 95% CI : −4.96, −0.47) and M1 to M4 (β=−10.19, P <.01; 95% CI : −12.22, −8.17). Type III increased from M1 to M3 (β=0.42, P =.003; 95% CI : 0.19, 0.65) and M1 to M4 (β=0.49, P =.002; 95% CI : 0.18, 0.81), Type IV increased from M1 to M4 (β=0.57, P <.01; 95% CI : 0.29, 0.84). A positive adaptation in AT structural integrity was observed over the XC season, with a ~10% shift from Type II to Type I UTC echo types, suggesting AT resilience to a competitive season of repetitive loading in highly trained runners.