Physical Impairments in Children With Chronic Renal Failure

This study is measuring and comparing physical health, muscle function, and exercise capacity in children and teenagers with chronic kidney failure versus healthy children of similar ages. The goal is to better understand how long-term kidney disease affects physical development and fitness in young people. **You may be eligible if...** - You are between 8 and 18 years old - You have been clinically stable for at least 3 weeks (if you have kidney failure) - You are physically and mentally able to complete the testing - You are willing to participate **You may NOT be eligible if...** - You have had any significant orthopedic, neurological, cardiovascular, or psychological issues in the past 6 months that would interfere with testing - You have had a kidney transplant - You smoke or have recently quit smoking - As a healthy participant: you have any chronic disease Talk to your doctor to see if this trial is right for you.