Tendon Structure Quantified using Ultrasound Imaging Differs Based on Location and Training Type.

Achilles tendinopathy is ten-times more common amongst running athletes compared to age-matched peers. Load induced tendon remodeling and its progression in an at-risk population of developing symptomatic tendinopathy is not well understood. The purpose of this study was to prospectively characterize Achilles and patellar tendon structure in competitive collegiate distance runners over different competitive seasons using quantitative ultrasound imaging. Twenty-two collegiate cross country runners and eleven controls were examined for this study. Ultrasound images of bilateral Achilles and patellar tendons were obtained near the start and end of the collegiate cross country season and the conclusion outdoor track season. Collagen organization, mean echogenicity, tendon thickness, and neovascularity were determined using well established image processing techniques. Achilles tendon collagen was less aligned in runners compared to controls (28% greater) but improved slightly (7% decrease) after the completion of the track season. Conversely, patellar tendons in runners were similar to control tendon throughout the cross-country season but underwent collagen alignment (17% decrease) and tendon hypertrophy (21% increase). Our findings indicate that Achilles tendon structure in trained runners differ structurally to control tendons but is stable throughout training while patellar tendon structure changes in response to the transition in training volume between cross country and track seasons. These findings expand upon prior reports that some degree of tendon remodeling may act as a protective adaptation for sport specific loading.