Sixteen Weeks of High-Speed Treadmill Running is Insufficient to Induce Achilles Tendinopathy in a Rat Model.

Despite the high prevalence of Achilles tendinopathy, clinically-relevant animal models of Achilles tendinopathy are lacking. Previous studies have demonstrated possible tendinopathic cell and matrix changes with high-speed treadmill running, but the consistency as well as functional and mechanical consequences of these changes were unclear. We sought to determine the applicability of this protocol as a tendinopathy model by defining changes in Achilles tendon structure, function, and mechanics associated with 16 weeks of high-speed treadmill running (26.8 m/min, 60 min/day, 5 days/week). We expected high-speed running would induce detrimental structural, functional, and mechanical changes that worsen over the course of the 16-week protocol. Treadmill running did influence bodyweight, hindlimb gait, and tendon cross-sectional area. However, contrary to our hypothesis, treadmill running did not induce tendinopathic changes in matrix organization, cell morphology, or tendon mechanics. As such, alternative strategies for robust and reproducible induction of Achilles tendinopathy in pre-clinical animal models are needed.