Concussion is a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces. From 2005 to 2010, approximately 7,000 Manitobans aged 14-18 years were diagnosed with a concussion. About half of all pediatric concussions occur during sport and our work shows that hockey is the most common sport resulting in a concussion among youth. OBJECTIVE - The overall objective of this study is to follow longitudinally two Winnipeg youth hockey teams to perform a comprehensive assessment of neurological, physiological, neuro-imaging, neuropsychological, and psychosocial functioning and measure these parameters before and after one hockey season and follow the two teams for a second season. We will examine these parameters among players who do and not sustain a concussion while playing hockey. INTERDISCIPLINARY TEAM - To accomplish our objectives, we will work within our recently established multi-disciplinary team of concussion researchers (CNCN). Our team includes a neurosurgeon who will treat all of the athletes (Dr Michael Ellis), a neuroanesthetist (Dr Alan Mutch) to conduct the MRI CO2 brain stress test, an exercise physiologist (Dean Cordingley) to conduct graded treadmill testing with an athletic therapist (Richard Girardin), a neuropsychologist (Dr Lesley Ritchie) to perform neuropsychological testing, and a sport injury epidemiologist (Dr Kelly Russell) who will provide methodological and statistical expertise. Additionally, we employ two research assistants.