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McCaffrey, Meghan A. M.A.; Mihalik, Jason P. M.S.; Crowell, Dean H. M.A.; Shields, Edgar W. Ph.D.; Guskiewicz, Kevin M. Ph.D.

doi: 10.1227/01.neu.0000306102.91506.8b
Clinical Studies

OBJECTIVE: It has been speculated that a theoretical injury threshold of 70 to 75 g may exist for concussions in football players. We aimed to investigate acute balance and neurocognitive performance after head impacts exceeding a theoretical injury threshold in the absence of both self-reported symptoms and a concussion diagnosis 24 hours before testing.

METHODS: Forty-three Division I collegiate football players participated in this double-blind, repeated-measures study. Subjects participated in three test sessions (baseline, low impact, and high impact) separated by at least 2 weeks. The Head Impact Telemetry System (Simbex, Lebanon, NH) recorded real-time head impacts sustained during practices and games. The Automated Neuropsychological Assessment Metrics assessed neurocognitive performance. The NeuroCom Sensory Organization Test (NeuroCom International Inc., Clackamas, OR) assessed postural stability. The Graded Symptom Checklist evaluated symptom presence and severity in our participants.

RESULTS: After the low-impact test session (<60 g), we observed improvements in the Math Processing (F1, 26 = 9.797; P = 0.004), Matching to Sample (F1, 26 = 6.504; P = 0.017), and Sternberg Procedure (F1, 26 = 5.323; P = 0.030) Automated Neuropsychological Assessment Metrics test modules. Statistically significant differences were also observed after the high-impact test session (>90g) with improvements in Math Processing (F1, 22 = 16.629; P < 0.001), Procedural Reaction Time (F1, 22 = 14.668; P < 0.001), and the total number of symptoms reported (F1, 22 = 10.267; P = 0.004). Neurocognitive improvements were likely attributed to a learning effect.

CONCLUSION: Our findings suggest that sustaining an impact greater than 90 g does not result in acute observable balance and neurocognitive deficits within 24 hours of sustaining the impact. Although previous studies have suggested a theoretical injury threshold, none have been founded on empirical data collected on the playing field in real-time. Future studies should consider the cumulative effects of impacts of varying magnitudes.

Department of Exercise and Sport Science, The University of North Carolina, Chapel Hill, North Carolina (McCaffrey) (Shields)

Department of Exercise and Sport Science, Curriculum in Human Movement Science, The University of North Carolina, Chapel Hill, North Carolina (Mihalik) (Guskiewicz)

Division of Sports Medicine, Campus Health Services, The University of North Carolina, Chapel Hill, North Carolina (Crowell)

Injury Prevention Research Center, The University of North Carolina, Chapel Hill, North Carolina (Guskiewicz)

Reprint requests: Kevin M. Guskiewicz, Ph.D., University of North Carolina at Chapel Hill, 209 Fetzer Gymnasium (CB# 8700), South Road, Chapel Hill, NC 27599. Email:

Received, March 30, 2007.

Accepted, July 24, 2007.

Copyright © by the Congress of Neurological Surgeons