"Abstract: Concussion is a type of mild traumatic brain injury, is common, and occurs both in sport and as a result of falls or accidents. Concussion has become an increasingly recognized public health concern, largely driven by prominent media coverage of athletes who have sustained concussion. Although much has been written about this condition, we still do not understand its natural history, and we are only now beginning to recognize that concussion often manifests in different clinical domains. These may require targeted treatment in and of themselves; otherwise, persistent postconcussive symptoms may develop. Although most individuals who sustain a concussion recover, and although concussion is a treatable condition, it is important that concussion be managed early and comprehensively to avoid a more prolonged clinical trajectory. A relatively recent term often used in the setting of concussion is repetitive head impact exposure-a biomechanical force applied to the head that does not generate a clinical manifestation of concussion, but may result in structural brain changes. Although it is often assumed that repetitive head impact exposure leads to long-term neurological sequelae, the science to document this assumption is in its infancy. Repeated concussions may lead to depression or cognitive impairment later in life, and there is an emerging literature that repeated concussion and repetitive head impact exposure are associated with chronic traumatic encephalopathy or other neurodegenerative diseases.

Currently there is no known causal connection between concussion, repetitive head impact exposure, and neurodegeneration, although this research is also still in its infancy. What is clear is that (a) concussion prevention and safety should be paramount in sport and in society, (b) concussion management should begin immediately and should include clinical domains, and (c) research on concussion and repetitive head impact exposure must continue to move forward. Keywords: concussion; mild traumatic brain injury; clinical domains; repetitive head impact exposure; chronic traumatic encephalopathy; safety"--.