Concussions can occur with or without LOC. In fact, the vast majority of concussions (more than 95% in a 2010 study of concussion among high school athletes)¹ do not result in LOC, a rate less than half the 10-11% reported in previous studies. 

Until the mid-2000's, however, LOC "featured prominently in published concussion severity scales [1] as being associated with more severe injuries."²Any LOC, however brief, caused the concussion to be classified [2] as a Grade 3 (severe) concussion. 

As sports concussion neuropsychologist and MomsTEAM expert Rosemarie Scolaro Moser, PhD [3], notes in her new book, Ahead of the Game [4], "It's not really hard to understand why for so long, loss of consciousness was considered an appropriate indicator of the severity of a concussion. After all, when an athlete has actually been knocked out, even if for a few seconds, it just seems like a more serious injury than one that leaves the athlete feeling only a little dazed." 

Recent studies on sport-related concussions, however, have consistently demonstrated that brief (less than 1 minute) LOC does not reflect injury severity or predict time to recovery, although the results of a large-scale study of extended (7 or more days) recovery in NFL players demonstrated that prolonged LOC (greater than 1 minute) was associated with delayed return to play.

As a result, the most recent consensus of sports concussion experts³ is that prolonged LOC (e.g. greater than one minute duration) provides preliminary evidence for caution so that it is listed as one of the "modifying" factors [5] that may influence management of such concussions.

In a 2010 statement on concussions,⁴ the American Academy of Pediatrics, however, takes a more conservative approach, stating that LOC lasting longer than 30 seconds may indicate a more significant intracranial injury.

For the most comprehensive, up-to-date concussion information on the Internet, click here [6].

1. Meehan W, d'Hemecourt P, Comstock D, "High School Concussions in the 2008-2009 Academic Year: Mechanism, Symptoms, and Management" Am. J. Sports. Med. 2010; 38(12): 2405-2409 (accessed December 2, 2010 at http://ajs.sagepub.com/content/38/12/2405.abstract?etoc).

2.Makdissi, M. Is the simple versus complex classification of concussion a valid and useful differentiation? Br. J. Sports Med. 2009; 43;123-127

3. McCrory P. et al. Consensus Statement on Concussion in Sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012 .Br. J. Sports Med. 2009; 47:250-258.

4. Halstead, M, Walter, K. "Clinical Report - Sport-Related Concussion in Children and Adolescents"  Pediatrics. 2010;126(3):597-615.

Most recently revised March 25, 2013 

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