Leg stiffness changes in athletes with Achilles tendinopathy

Overuse injuries of the Achilles tendon cause impairment in lower leg muscle-tendon function. The purpose of this study was to evaluate leg stiffness in patients suffering unilateral Achilles tendinopathy. 51 athletes with unilateral Achilles tendinopathy underwent leg stiffness testing by modeling the vertical ground reaction force in a contact mat, measuring flight and contact time during hopping. Clinical status was estimated with a pain VAS and a validated questionnaire (VISA-A). The 'leg stiffness ratio' (LSR=stiffness of injured leg/stiffness of healthy leg) was calculated to determine the relative patient affectation and for intra-group comparison. 84 percent of subjects showed lower leg stiffness in the affected side during hopping. Leg stiffness was significantly lower in the limb affected by Achilles tendinopathy than in the healthy side (14.07±3.74 kN/m vs. 15.61±4.01 kN/m, p=0.047); overall LSR was 0.90±0.09. Intra-group comparison did not show significant differences related to patients' age, gender, sport level, and site of tendon injury (midportion or insertional). Leg stiffness was significantly reduced in patients with unilateral Achilles tendinopathy probably related to increasing ankle compliance. Regular leg stiffness assessment would be beneficial for athletes suffering Achilles tendon problems in terms of quantifying performance capabilities and providing objective data for a safer return to sport activity.