Project Summary/Abstract Ankle contractures in muscular dystrophy: mechanisms and tissue adaptations Duchenne muscular dystrophy (DMD) is a genetic disorder that causes progressive muscle degeneration and weakness leading to difficulties walking, using the arms, and breathing. In addition to muscle weakness, individuals with muscular dystrophy often lose flexibility in joints such as their ankles, knees, hips, elbows, and hands. This loss of range of motion, called a contracture, can cause difficulty with function, positioning, and comfort. The loss of ankle joint range of motion and development of plantarflexion contractures affects nearly all children with DMD while they are still able to walk, and contracture prevention and management is a major goal of rehabilitation for ambulatory children with DMD to allow for maximal function and quality of life. However, there is little convincing evidence to demonstrate that currently prescribed contracture interventions are effective or improve function, and this is likely due to a gap in knowledge about the pathophysiology of contracture development in DMD. The goal of this proposal is to prospectively evaluate the potential mechanisms driving loss of ankle range of motion in DMD and the plantarflexor muscle and/or tendon changes that result. Our central hypothesis is that progressive proximal muscle weakness and degeneration drives ankle contracture development in ambulatory children with DMD and that the primary adaptation in the plantarflexor muscle-tendon unit is shortening of the Achilles tendon. In aim 1, we will quantitatively evaluate lower extremity muscle strength and muscle replacement by fat using magnetic resonance imaging (MRI) to evaluate the impact of muscle weakness and degeneration on ankle joint dorsiflexion range of motion in ambulatory individuals with DMD. In aim 2, we will evaluate the tissue adaptations occurring alongside loss of joint range of motion including changes in plantarflexor muscle length, Achilles tendon length, Achilles tendon structure, and muscle-tendon passive stiffness. Data collected from this study will help physical therapists and other rehabilitation professionals better understand the causes of ankle contractures in muscular dystrophy, which will lead to more evidence-based decisions about targeted interventions that may help prevent or slow contracture formation.