HE HIGH INCIDENCE OF CEREbral concussion in contact sports is well documented. 1-8 According to the Centers for Disease Control and Prevention, approximately 300000 sport-related concussions occur annually in the United States, 9 and the likelihood of serious sequelae may increase with repeated head injury. 10 Recent publications addressing the negative consequences of recurrent concussion in sports raise questions regarding the potential longterm sequelae associated with this injury, 11-13 and recurrent concussion has forced several collegiate and professional athletes to retire early from their respective sports. Studies from the 1970s report annual concussion incidence rates in high school football to be as high as 15% to 20% of all players in a season, 5,8 while annual incidence estimates of 10% were reported in collegiate football during the late 1980s. 14 More recently, lower in

TUDIES IN BASIC NEUROSCIENCEhave demonstrated that mild traumatic brain injury (concussion) is followed by a complex cascade of ionic, metabolic, and physiological events that can adversely affect cerebral function for several days to weeks. 1,2 Concussive brain injuries trigger a pathophysiological sequence characterized earliest by an indiscriminate release of excitatory amino acids, massive ionic flux, and a brief period of hyperglycolysis, followed by persistent metabolic instability, mitochondrial dysfunction, diminished cerebral glucose metabolism, reduced cerebral blood flow, and altered neurotransmission. These events culminate in axonal injury and neuronal dysfunction. [2][3][4][5] Clinically, concussion eventuates in neurological deficits, cognitive impairment, and somatic symptoms. 6 Sport-related concussion is now widely recognized as a major public health concern in the United States and worldwide. 3,[7][8][9] Despite rule changes and advances in protective equipment, the incidence rate of concussion in contactAuthor Affiliations are listed at the end of this article.

Clinical decision making about an athlete's return to competition after concussion is hampered by a lack of systematic methods to measure recovery. We applied standard regression-based methods to statistically measure individual rates of impairment at several time points after concussion in college football players. Postconcussive symptoms, cognitive functioning, and balance were assessed in 94 players with concussion (based on American Academy of Neurology Criteria) and 56 noninjured controls during preseason baseline testing, and immediately, 3 hr, and 1, 2, 3, 5, and 7 days postinjury. Ninety-five percent of injured players exhibited acute concussion symptoms and impairment on cognitive or balance testing immediately after injury, which diminished to 4% who reported elevated symptoms on postinjury day 7. In addition, a small but clinically significant percentage of players who reported being symptom free by day 2 continued to be classified as impaired on the basis of objective balance and cognitive testing. These data suggest that neuropsychological testing may be of incremental utility to subjective symptom checklists in identifying the residual effects of sport-related concussion. The implementation of neuropsychological testing to detect subtle cognitive impairment is most useful once postconcussive symptoms have resolved. This management model is also supported by practical and other methodological considerations.

The use of self or combination modeling is more effective than is expert-only modeling for the implementation of instructional programs aimed at reducing the risk of jump-landing anterior cruciate ligament injuries.