This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Plyometric exercise encompasses running, jumping and agility activities and is used in anterior cruciate ligament-ACL reconstruction rehabilitation to prepare patients for sports participation. However, clinical protocols have not been scientifically tested to quantify functional gains, and high forces during plyometric exercise might contribute to knee osteoarthritis development. The primary objective of this application is to examine how plyometric exercise intensity during ACL reconstruction rehabilitation affects knee function and articular cartilage metabolism. Our central hypothesis is that knee function and articular cartilage degradation will increase in a dose-dependent manner with the intensity of plyometric exercise during ACL reconstruction rehabilitation. Secondarily, we will examine the effect of plyometric exercise intensity on impairments after ACL reconstruction. Thirty patients that are 12 weeks post-operative ACL reconstruction and meet standard criteria for advanced rehabilitation will participate in the study. Subjects will be recruited, receive interventions and be tested at the UF &Shands Orthopaedics and Sports Medicine Institute. Testing will consist of questionnaires, functional performance testing, isokinetic testing, movement analysis during a jump-landing task and knee athrometry. The College of Public Health and Health Professions Research Complex will be used for movement analysis if needed. In addition, urine and blood samples will be collected at the UF General Clinical Research Center. This randomized clinical trial aligns well with the NFL Charities'mission to support research on sports injury treatment that will benefit individuals involved in competitive sports and recreational athletic activities.