Abstract
Achilles tendinopathy affects many running athletes and often leads to chronic pain and functional deficits. Although changes in tendon structure have been linked with tendinopathy, the effects of distance running on tendon structure are not well understood. Therefore, the purpose of this study was to characterize structural differences in the Achilles tendons in healthy young adults and competitive distance runners using quantitative ultrasound analyses. We hypothesized that competitive distance runners with no clinical signs or symptoms of tendinopathy would have quantitative signs of tendon damage, characterized by decreased collagen alignment and echogenicity, in addition to previous reports of thicker tendons. Longitudinal ultrasound images of the right Achilles tendon midsubstance were acquired in competitive distance runners and recreationally active adults. Collagen organization, mean echogenicity, and tendon thickness were quantified using image processing techniques. Clinical assessments confirmed that runners had no signs or symptoms of tendinopathy, and controls were only included if they had no history of Achilles tendon pain or injuries. Runner tendons were 40% less organized, 48% thicker, and 41% less echogenic compared with the control tendons ( P < 0.001). Young adults engaged in competitive distance running have structurally different tendons than recreationally active young adults. NEW & NOTEWORTHY In this study, we quantified the Achilles tendon substructure in distance runners, and a control group of young adults, to determine whether distance running elicits structural adaptations of the tendon. We found that competitive distance runners have structurally compromised Achilles tendons despite not showing any clinical signs or symptoms of tendon injury. These findings suggest that distance running may stimulate structural changes as a protective mechanism against tendon pain and dysfunction.
Highlights
Midsubstance Achilles tendinopathy is among the most commonly reported injuries in running athletes [24]
Some runners had reported dealing with running-related pain either at the time of the study or previously; these reported events did not originate in the Achilles tendon
Achilles tendon structure differs in competitive-distance runners compared with recreationally active young adults despite no clinical presentation of midsubstance tendinopathy or pain
Summary
Midsubstance Achilles tendinopathy is among the most commonly reported injuries in running athletes [24]. Repetitive tendon loading as high as 12 times body weight [10] is thought to elicit structural changes observed in tendinopathy development. This overuse injury presents with pain and swelling of the tendon 4 – 6 cm proximal to the calcaneal insertion, which leads to upward of a 50% decrease in the elastic modulus of the tendon [4]. While structural changes elicited by tendinopathy, in both human and animal tendon, have been characterized using histological and imaging techniques [39], these invasive measurements are not practical to employ in clinical settings
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