About Sports Concussion

Concussion knowledge and application of practical guidelines in sport are based on current international concussion opinion 1-3 . A recent exponential increase in the number of concussion publications in the literature has been summarized in these consensus documents. It should be noted that the science of concussion continues to evolve. Current paradigms should be critically evaluated and periodically reviewed.

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Woman’s Lacrosse

What is concussion?

Concussion is a disturbance in the brain’s ability to acquire and process information. The reduced function of the brain represents damage to nerve cells (neurons). The neurons can be damaged by a direct blow to the head, which causes the brain to rotate and/or move forward and backward. Indirect impact to the body can transfer an impulsive force to the brain which damages neurons.

The effect that this has on the athlete can vary from person to person, depending on which part of the brain is affected. The impact can cause concussion signs visible to others.

Concussion should be suspected if these signs are observed: 4

  • Unresponsiveness
  • Upper limb muscle rigidity
  • Upper limb spontaneous movement
  • A fit / seizure soon after contacting the surface
  • Balance difficulty
  • Slow responses
  • Vacant stare
  • Confusion
  • Disorientation
  • Holding the head
  • Facial injury
  • Speech slurring


Minutes to hours after the impact injury the player may complain of:

  • Headache
  • Nausea / Vomiting
  • Blurred vision
  • Memory loss / difficulty
  • Dizziness
  • Tiredness
  • Not feeling right
  • Sensitive to bright light & loud noise


Days to weeks after the impact the player could have/feel:

  • Sleep difficulty
  • Persistent low grade headache
  • Poor attention & concentration
  • Sad or irritable or frustrated
  • Tired easily
  • Lethargic, low motivation

Minimum diagnostic criteria for concussion 5

  • Physical signs occurring following an impact – LOC, convulsion, balance difficulty.
  • Physical signs observed by others – slowness with Q’s, aggression, emotional lability, incorrect play, vacant stare, glassy eyes.
  • Any concussion symptoms.
  • Any neurological / balance and cognitive examination (poor planning, unable to switch mental set 6, impaired memory & learning 7;8, reduced attention & processing information 9-12, slow reaction times 13-16

Concussion cannot be diagnosed at one point in time. Symptoms can evolve over time. Perform serial assessments over time and rule out other conditions that can mimic concussion.

The severity of traumatic brain injury is measured according to the Glasgow Coma Scale at 6h after head injury. In the neurosurgical spectrum of mild traumatic brain injury (mTBI) the Glasgow Coma Scale ranges from 13-15. mTBI is characterize by a neurological deficit and     structural injury seen on CT/MRI scan.

Athletes with concussion signs and symptoms have a Glasgow Coma Scale ranging from 14 – 15 and rarely is structural injury seen on CT/MRI.

Pathophysiology and Window of Vulnerability 18;19

The following changes in the brain are implicated in concussion: Δ pattern of neuron conduction 20-22; Δ glucose metabolism 23-27; Δ membrane protein expression 28-31; Δ blood flow. The net effect is an energy deficit characterized by an acidosis and reduced neuronal activity.

An indirect marker of brains energy balance is N – acetylaspartate (NAA). NAA is measured using proton magnetic resonance spectroscopy (MRS). NAA is an index of metabolic recovery after concussion in humans. 32 This can explain the why some athletes display significant cognitive problems while conventional scans lack sensitivity to detect neurotransmitters.

NAA levels were found to be decreased for up to 30 days after concussion, long after the athlete became asymptomatic. 33 It was found that non concussed athletes may also have low NAA levels presumably due to sub concussive impacts. 34 In simple terms, while there is not enough energy, the brain can’t make NAA. The glucose deficit can also cause mitochondrial dysfunction, more likely with a second impact during the window of vulnerability.  35


How common is concussion?

1.6 to 3.8 million concussions occur in sport per year in the United States. 36 Across football codes in Australia, the probability of concussion is approximately 1 in 7.


Available Resources

For further information on concussion visit www.sportsconcussionaustralasia.com



(1)    McCrory P, Meeuwisse WH, Aubry M, Cantu B, Dvorak J, Echemendia RJ 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 2013; 47(5):250-258.

(2)    Harmon KG, Drezner JA, Gammons M, Guskiewicz KM, Halstead M, Herring SA et al. American Medical Society for Sports Medicine position statement: concussion in sport. Br J Sports Med 2013; 47(1):15-26.

(3)    Patricios J, Collins R, Branfield A, Roberts C, Kohler R. The sports concussion note: should SCAT become SCOAT? Br J Sports Med 2012; 46(3):198-201.

(4)    Kelly JP, Rosenberg JH. The development of guidelines for the management of concussion in sports. J Head Trauma Rehabil 1998; 13(2):53-65.

(5)    McCrory P, Meeuwisse WH, Echemendia RJ, Iverson GL, Dvorak J, Kutcher JS. What is the lowest threshold to make a diagnosis of concussion? Br J Sports Med 2013; 47(5):268-271.

(6)    Matser EJ, Kessels AG, Lezak MD, Jordan BD, Troost J. Neuropsychological impairment in amateur soccer players. JAMA 1999; 282(10):971-973.

(7)    Gronwall D, Wrightson P. Memory and information processing capacity after closed head injury. J Neurol Neurosurg Psychiatry 1981; 44:889-895.

(8)    Lovell M, Collins M, Bradley J. Return to play following sports-related concussion. Clin Sports Med 2004; 23(3):421-41, ix.

(9)    Gronwall D, Wrightson P. Cumulative effect of concussion. Lancet 1975; 2(7943):995-997.

(10)    Peterson CL, Ferrara MS, Mrazik M, Piland S, Elliott R. Evaluation of neuropsychological domain scores and postural stability following cerebral concussion in sports. Clin J Sport Med 2003; 13(4):230-237.

(11)    Hinton-Bayre AD. Choice of reliable change model can alter decisions regarding neuropsychological impairment after sports-related concussion. Clin J Sport Med 2012; 22(2):105-108.

(12)    Hinton-Bayre AD, Geffen G, McFarland K. Mild head injury and speed of information processing: a prospective study of professional rugby league players. J Clin Exp Neuropsychol 1997; 19(2):275-289.

(13)    Moriarity J, Collie A, Olson D, Buchanan J, Leary P, McStephen M et al. A prospective controlled study of cognitive function during an amateur boxing tournament. Neurology 2004; 62(9):1497-1502.

(14)    Makdissi M, Collie A, Maruff P, Darby DG, Bush A, McCrory P et al. Computerised cognitive assessment of concussed Australian Rules footballers. Br J Sports Med 2001; 35(5):354-360.

(15)    Warden DL, Bleiberg J, Cameron KL, Ecklund J, Walter J, Sparling MB et al. Persistent prolongation of simple reaction time in sports concussion. Neurology 2001; 57(3):524-526.

(16)    Collins MW, Iverson GL, Lovell MR, McKeag DB, Norwig J, Maroon J. On-field predictors of neuropsychological and symptom deficit following sports-related concussion. Clin J Sport Med 2003; 13(4):222-229.

(17)    McCrory PR, Berkovic SF. Concussion: the history of clinical and pathophysiological concepts and misconceptions. Neurology 2001; 57(12):2283-2289.

(18)    Hovda DA, Lee SM, Smith ML, Von SS, Bergsneider M, Kelly D et al. The neurochemical and metabolic cascade following brain injury: moving from animal models to man. J Neurotrauma 1995; 12(5):903-906.

(19)    Longhi L, Saatman KE, Fujimoto S, Raghupathi R, Meaney DF, Davis J et al. Temporal window of vulnerability to repetitive experimental concussive brain injury. Neurosurgery 2005; 56(2):364-374.

(20)    Giza CC, Hovda DA. The Neurometabolic Cascade of Concussion. J Athl Train 2001; 36(3):228-235.

(21)    Katayama Y, Becker DP, Tamura T, Hovda DA. Massive increases in extracellular potassium and the indiscriminate release of glutamate following concussive brain injury. J Neurosurg 1990; 73(6):889-900.

(22)    Shaw NA. The neurophysiology of concussion. Prog Neurobiol 2002; 67(4):281-344.

(23)    Fineman I, Hovda DA, Smith M, Yoshino A, Becker DP. Concussive brain injury is associated with a prolonged accumulation of calcium: a 45Ca autoradiographic study. Brain Res 1993; 624(1-2):94-102.

(24)    Kawamata T, Katayama Y, Hovda DA, Yoshino A, Becker DP. Lactate accumulation following concussive brain injury: the role of ionic fluxes induced by excitatory amino acids. Brain Res 1995; 674(2):196-204.

(25)    Yoshino A, Kawamoto M, Yoshida T, Kobayashi N, Shigemura J, Takahashi Y et al. Activation time course of responses to illusory contours and salient region: a high-density electrical mapping comparison. Brain Res 2006; 1071(1):137-144.

(26)    Yoshino A, Kawamoto M, Yoshida T, Kobayashi N, Shigemura J, Takahashi Y et al. Activation time course of responses to illusory contours and salient region: a high-density electrical mapping comparison. Brain Res 2006; 1071(1):137-144.

(27)    Yoshino A, Hovda DA, Kawamata T, Katayama Y, Becker DP. Dynamic changes in local cerebral glucose utilization following cerebral conclusion in rats: evidence of a hyper- and subsequent hypometabolic state. Brain Res 1991; 561(1):106-119.

(28)    Nilsson B, Nordstrom CH. Rate of cerebral energy consumption in concussive head injury in the rat. J Neurosurg 1977; 47(2):274-281.

(29)    Nilsson B, Nordstrom CH. Experimental head injury in the rat. Part 3: Cerebral blood flow and oxygen consumption after concussive impact acceleration. J Neurosurg 1977; 47(2):262-273.

(30)    Nilsson B, Ponten U. Exerimental head injury in the rat. Part 2: Regional brain energy metabolism in concussive trauma. J Neurosurg 1977; 47(2):252-261.

(31)    Nilsson B, Ponten U, Voigt G. Experimental head injury in the rat. Part 1: Mechanics, pathophysiology, and morphology in an impact acceleration trauma model. J Neurosurg 1977; 47(2):241-251.

(32)    Moreno A, Bluml S, Hwang JH, Ross BD. Alternative 1-(13)C glucose infusion protocols for clinical (13)C MRS examinations of the brain. Magn Reson Med 2001; 46(1):39-48.

(33)    Vagnozzi R, Signoretti S, Tavazzi B, Floris R, Ludovici A, Marziali S et al. Temporal window of metabolic brain vulnerability to concussion: a pilot 1H-magnetic resonance spectroscopic study in concussed athletes–part III. Neurosurgery 2008; 62(6):1286-1295.

(34)    Chamard E, Theoret H, Skopelja EN, Forwell LA, Johnson AM, Echlin PS. A prospective study of physician-observed concussion during a varsity university hockey season: metabolic changes in ice hockey players. Part 4 of 4. Neurosurg Focus 2012; 33(6):E4-E7.

(35)    Vagnozzi R, Tavazzi B, Signoretti S, Amorini AM, Belli A, Cimatti M et al. Temporal window of metabolic brain vulnerability to concussions: mitochondrial-related impairment–part I. Neurosurgery 2007; 61(2):379-388.

(36)    Langlois JA, Rutland-Brown W, Wald MM. The epidemiology and impact of traumatic brain injury: a brief overview. J Head Trauma Rehabil 2006; 21(5):375-378.




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