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. With the demands of training, practice and competition over a year, typical of most collegiate athletic teams, the changes in various tests of athletic or sport performance are an important indicator of fatigue, stress or performance decrements and improvements. These tests can help to determine: 1) if training goals are being met, 2) if there is a need to change short-term exercise prescriptions or practice schedule demands (possibly incorporating more time for rest and recovery), and 3) if there is a need to alter long-term training cycles. The purpose of this study is to comprehensively identify performance and stress characteristics, over a 9-month period, of a NCAA Division 1 men's volleyball team. Members of the UC Irvine men's intercollegiate volleyball team will be recruited for this study. Measures of exercise ability particularly relevant to volleyball performance will be examined at pre-season (mid-December), mid-season (early March), post-season (late-May), and following summer break (late-August). Fasting, pre-exercise and post-exercise blood samples will be obtained at selected times to examine complete blood count (CBC), metabolic (e.g. lactate), hormonal (e.g. cortisol, growth hormone, IGF-1), immune (e.g. cytokines/chemokines), adhesion molecule, and heat shock protein indicators of the physiological demands and stress that occurs across this 9-month period, and in response to actual competition. DEXA measurements, and MRI assessments of the knees, will be conducted at selected times to evaluate changes in body composition and joint health, respectively. This will be the most thorough study to date on the physiological and immune response to volleyball training and competition, and will provide unique insights into the physical development and longitudinal changes in these student athletes.