Research Review By Dr. Jeff Muir©


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Date Posted:

September 2019

Study Title:

American Medical Society for Sports Medicine position statement on concussion in sport


Harmon KG, Clugston JR, Dec K, Hainline B, Herring S et al.

Author's Affiliations:

Departments of Family Medicine and Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington; Departments of Community Health and Family Medicine and Neurology, University of Florida, Gainesville, Florida; Department of Physical Medicine and Rehabilitation, and Orthopaedic Surgery, Virginia Commonwealth University, Richmond, Virginia; National Collegiate Athletic Association (NCAA), Indianapolis, Indiana; Department of Rehabilitation Medicine, University of Washington, Seattle, Washington; Department of Family Medicine, University of North Carolina, Chapel Hill, North Carolina; Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania; UBMD Department of Orthopaedics and Sports Medicine, State University of New York at Buffalo, Buffalo, New York; Departments of Neurosurgery and Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin; Department of Family Medicine and Orthopedics, University of Colorado, Denver, Colorado; Internal Medicine/Sports Medicine, Rutgers Robert Wood Johnson Medical School, Princeton University, University Health Services, New Brunswick, New Jersey; Princeton University, University Health Services, Princeton, New Jersey; Department of Orthopedics, University of Colorado, Aurora, Colorado; Department of Family Medicine and Community Health, University of Minnesota, Minneapolis, Minnesota – all in the USA.

Publication Information:

British Journal of Sports Medicine 2019; 53: 213–225.

Background Information:

Sports-related concussion (SRC) is an important topic for sports medicine and other clinicians and one that has gained considerable attention in recent years. The American Medical Society for Sports Medicine (AMSSM) first published a position statement on the management of SRC in 2013 (1), providing information on diagnosis, treatment and management. This position statement is an update to that document and was a narrative review on new and existing evidence and best practices for SRC.


Definition of Concussion:

Concussion is defined as a traumatic, transient disturbance of brain function that involves a complex pathophysiological process (1). Concussion is considered a subset of mild traumatic brain injury (MTBI) (1) and a condition whose symptoms cannot be explained by drugs, alcohol, medication use or other injuries (2, 3).


An estimated 1.0-1.8 million SRCs per year occur among those aged 0-18 years, about 400,000 of which occur in high school athletes (8). It is further estimated that > 50% of concussions in high school-aged youth are unrelated to organized sports, with only 20% of concussions related to organized school sports (8).


While not fully understood, the pathophysiology of concussion has been described as force delivered to the brain causing disruptive stretching of neuronal cell membranes and axons, causing a complex cascade of ionic, metabolic and pathophysiological events (4). The cumulative effect of repeated injury has been demonstrated in animal models, where repeated insults can result in worsening cellular metabolic changes and more significant deficits (5-7).


Diagnosis of SRC can be difficult and is based largely on clinical assessment, which is complicated by the lack of validated, objective diagnostic tests. Further, clinicians must often rely heavily on patient self-reporting.

Preseason Testing:
Preparticipation physical evaluation (PPE), including a concussion history (number, recovery course and interval between injuries) plus evaluation of comorbid conditions is important in establishing preinjury protocols.

Several pre-play testing procedures exist to capture baseline data; however, there is considerable variation in test performance with repeated testing in non-injured athletes (9, 10). The rapid development of young athlete’s brains also makes establishing meaningful baseline measures difficult. Interestingly, repeat annual baseline testing is no longer recommended for NCAA collegiate athletes, based on the lack of repeatable findings (11).

Sideline Assessment:
Immediate removal from play for assessment is required in instances where loss of consciousness (LOC), impact seizure, tonic posturing, gross motor instability, confusion or amnesia are observed. Removal should be considered in cases where the injury was directly observed but also where video review indicates the potential for concussion, based on injury mechanics and potential presence of LOC, motor incoordination, balance problems or having a blank or vacant look.

Symptoms are the most sensitive indicator of concussion (9, 12) and are especially relevant in sideline assessment. Self-assessment, however, is complicated by a potential lack of recognition of signs/symptoms, or conscious false reporting to prevent removal from play. The onus is on the clinician to determine the suitability to remain in the game and/or return to play. Any increase in symptoms after a suspected concussion requires further evaluation.

Office/Subacute Assessment:
In-office assessment should include a history and neurological exam (with details of injury mechanism, symptom progression, neurocognitive functioning, sleep disturbances, vestibular/ocular function, gait/balance and a cervical spine assessment). Sideline assessment utility decreases within as little as 3 days, so in-office assessment should be comprehensive and thorough.

New Assessment/Monitoring Tools:

Emerging Sideline Tools:
New tests based on vestibular-ocular function and reaction time have been proposed. The King-Devick (KD) test involves timed saccadic eye movement testing, requiring the rapid reading aloud of numbers. Simple reaction time tests (e.g. using a dropped weighted stick) have also been suggested. App-based technologies measuring reaction time have also been proposed, although this area in general requires significant further research.

Impact Sensors:
Sensors measuring acceleration and impact forces used during play may not consistently record head impacts and provide only information regarding the mechanisms of impact. They cannot diagnose concussion, as reactions to impact are subjective. To illustrate, some athletes experience/withstand high forces without consequence and others suffer injury from relatively low impact forces.

Concussion Biomarkers:
Imaging (CT, MRI) is rarely used to diagnosis concussion. Fluid biomarkers (blood, saliva, cerebrospinal fluid) as diagnostic tools is under investigation. Testing of proteomic markers of injury have shown some promise; however, the overall level of evidence supporting their use is low. More research in this area is needed.

Clinical Profiles for SRC Patients:
The use of clinical profiles or clinical domains to categorize concussion presentations is a new concept. The heterogeneity of presentations; however, make categorization difficult. Also, SRC symptoms often present with characteristics of several profiles, which further complicates this approach to injury monitoring. Additional research in this area is warranted.

Concussion Management:

Natural Course:
SRC symptoms respond and improve spontaneously, often within 2 weeks, in 80-90% of cases (13). In younger athletes, resolution may require 4 weeks from the time of injury (14). Proper communication with patients of expectations and tracking of symptoms via checklists are important considerations for the clinician.

Predicting Recovery:
The number and severity of acute and subacute symptoms is the best predictor of recovery in SRC. Subacute headache and depression are risk factors for recovery periods of > 1 month (15). Preinjury mental health problems (depression) increase the likelihood of prolonged recovery (14), while learning disabilities/ADHD do not appear to increase recovery time (15).

Treatment of Concussion:

Prescribed Rest:
Prescribed cognitive and physical rest have been the basis of treatment for decades; however, the evidence supporting this approach is equivocal! Animal studies have demonstrated conflicting benefits of rest and early return to exercise (16, 17). In human studies, strict rest slowed recovery and led to increased chance of prolonged symptoms (18). “Dark room” or “cocoon therapy” have even been associated with adverse mental effects and are no longer recommended (2). Current recommendations are for 24-48 hours of symptom-limited cognitive and physical rest, followed by a gradual increase in activity, staying below symptom exacerbation thresholds (2).

Activity and Exercise:
Exercise intolerance appears to relate to impaired autonomic functioning and control of cerebral blood flow, which are increased with exercise (19). Early sub-symptom threshold exercise appears to improve recovery in acute concussion (20, 21), although more research is required. Note that early exercise does not replace a graded return to sport protocol.

Early evidence in animal studies indicates a potential role for nutraceuticals such as B-vitamins, omega-3 fatty acids, vit D, progesterone, N-Methyl-D-aspartate (NMDA) and for dietary manipulations (e.g. ketogenic diet), although this research is in the early stages and no significant human research data is available.

Persistent Post-Concussion Symptoms:

Persistent post-concussive symptoms (PPCS) is the preferred term for symptoms that persist beyond 2 weeks in adults and 4 weeks in children. The use of “post-concussion syndrome” has fallen out of favour.

Targeted Treatment:
Vestibular, oculomotor, psychological, sleep, cervical and autonomic nervous system evaluations have been suggested as areas of testing for PPCS management.

Exercise for Persistent Post-Concussive Symptoms:
Sub-symptom threshold exercise has been recommended for those with persistent concussion symptoms. The Buffalo Concussion Exercise Treatment Protocol is the most robustly studied program of this nature (22).

Physical Therapy, Vestibular Therapy and Collaborative Care:
Targeted physical therapy (or chiropractic care) addressing cervical spine and/or vestibular dysfunction has been shown to improve PPCS (23, 24). Cognitive work should remain below symptom aggravation levels. Sleep disturbances should be addressed with non-pharmacological or pharmacological strategies.


SRC can result in changes to attention, concentration, short-term memory, cognitive functioning and executive function – all of which can impact learning. Many athletes return to the classroom with little or no interruption of classroom time. Schools should, however, be prepared to provide additional support (e.g. individualized return-to-learn plans) for athletes experiencing persistent symptoms, based on symptom-limited learning activities. Classroom adjustments could include:
  • Breaks as needed
  • Reduced workload or modify due dates
  • Increased time allotted for task or test completion
  • Delay exams or allow writing in a separate, distraction-free environment
  • Allow use of headphones or earplugs to reduce noise sensitivity
  • Allow sunglasses to reduce light sensitivity
  • Limit electronic screen use
  • Allow student to leave early to avoid crowded and noisy hallways
Return to sporting activities should follow a successful return to the classroom for student athletes.


Symptoms should resolve before returning to sport. Return-to-play involves a stepwise increase in physical demands in a sport-specific manner, without a return of symptoms. Psychological readiness for return to play is also a requirement. In general, each stage progression should be followed by at least 24 hrs without symptom return before progressing to the next stage. The steps in this process are:
  1. Symptom-limited activity: reintroduction of normal activities of daily living (symptoms cannot worsen with activity).
  2. Light aerobic exercise: walking, stationary bike, controlled activities that raise the heart rate.
  3. Sport-specific activity: running, skating or other activities with no risk of head impact.
  4. Non-contact training drills: sport-specific, non-contact drills involving increased coordination and thinking. Progressive increase in resistance training.
  5. Full contact practice: return to normal training activities with assessment of psychological readiness to return.
  6. Return to sport.

Preliminary evidence suggests that driving impairment can occur in patients following SRC (25), although there is very little evidence in the literature.

Risks Related to SRC:

Short-Term Risks:
Early return to play increases the risk of worsening symptoms and prolonged recovery (26), plus increases the risk of repeated concussion (27). The ‘second impact syndrome’ remains both rare and controversial, yet remains a potentially life-threatening consequence of reinjury that appears primarily limited to pediatric and adolescent athletes. Some research indicates that early return to play may also increase the risk of musculoskeletal injury (28).

Long-Term Risks:
Mental health problems and depression have been demonstrated in low quality evidence, with former NFL and college football players with a concussion history demonstrating an increased likelihood of experiencing depression, despite the risk of mental health issues being lower than age-matched controls (29).

Chronic traumatic encephalopathy (CTE) has been described in former athletes with a history of concussion, but the comparative prevalence in the non-athlete population is unknown. A cause-and-effect relationship between post-mortem CTE changes and antemortem behaviour has not been established. CTE-associated symptoms may be related to impact load and type and length of athletic career but may also be related to genetic factors, lifestyle factors (drug/alcohol use), general health, psychiatric disease and other factors. The most widely described risk factor is exposure to both multiple concussions and repetitive head impacts, but this is also likely specific to each individual and subject to multiple factors (30). The authors suggest that athletes (current and former) presenting with neuropsychiatric symptoms ascribed to CTE should be assessed for potential comorbid conditions before being assumed to have CTE (31).

Repetitive sub-concussive head impacts are suspected to contribute to long term prognosis and potential CTE; however, the long-term effects of sub-concussive impacts cannot be accurately assessed with current technology.

Disqualification from Sport:

There are no evidence-based guidelines for disqualifying an athlete from future participation in sport due to concussion. Decisions to retire from competition should be made on an athlete-by-athlete basis, based on the multiple factors discussed in this review and those relating to the individual patient/athlete.

Prevention of Concussions:

Prevention is ultimately more effective than treatment for SRC. Rule changes, technique changes and equipment modifications have been suggested as valuable preventive methods. Some evidence exists to indicate that delaying introduction of body-checking decreases concussions in hockey players (32), and that practice modification and changes in tackling technique may decrease concussion in football (33). Mouthguards have not proven valuable in preventing concussion and should be used primarily to prevent dental injury (34). Helmets prevent skull trauma and intracranial bleeding but provide minimal protection against concussion. It is noteworthy that players’ wearing of new or “improved” protective equipment may encourage a more aggressive style of play, potentially increasing the risk for injury.

Clinical Application & Conclusions:

Sports-related concussion (SRC) is a complex, multifactorial condition that generally resolves within 1-4 weeks of injury. Diagnosis is made more difficult by reliance on self-reporting of symptoms. After 24-48 hrs of rest, gradual return to exercise, in a sub-symptom threshold manner, is recommended. In cases of prolonged symptoms, a multidisciplinary approach to diagnosis and treatment should be considered. Further research into all aspects of SRC treatment and prevention is still required.

Study Methods:

This was a narrative literature review, so no formal outline of their study methods was presented.

Study Strengths / Weaknesses:

  • Comprehensive review providing an excellent summary of available evidence.
  • Focus on diagnosis and management is helpful for all clinicians, regardless of discipline or training.
  • Narrative nature of review provides little analysis of actual data in this area.
  • Uncertainty and/or lack of robust evaluation for many tests/procedures limits the ability to apply conclusions and recommendations broadly.

Additional References:

  1. Harmon KG, Drezner JA, Gammons M, et al. American Medical Society for Sports Medicine position statement: concussion in sport. Br J Sports Med 2013; 47: 15–26.
  2. McCrory P, Meeuwisse W, Dvorak J, et al. Consensus statement on concussion in sport – the 5th international conference on concussion in sport held in Berlin. Br J Sports Med 2016; 51: 838–47.
  3. McCrory P, Feddermann-Demont N, Dvořák J, et al. What is the definition of sports related concussion: a systematic review. Br J Sports Med 2017; 51: 877–87.
  4. Barkhoudarian G, Hovda DA, Giza CC. The Molecular Pathophysiology of Concussive Brain Injury - an Update. Phys Med Rehabil Clin N Am 2016; 27: 373–93.
  5. Vagnozzi R, Tavazzi B, Signoretti S, et al. Temporal window of metabolic brain vulnerability to concussions: mitochondrial-related impairment--part I. Neurosurgery 2007; 61: 379–88.
  6. Vagnozzi R, Signoretti S, Tavazzi B, 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: 1286–95.
  7. Longhi L, Saatman KE, Fujimoto S, et al. Temporal window of vulnerability to repetitive experimental concussive brain injury. Neurosurgery 2005; 56: 364–74.
  8. Bryan MA, Rowhani-Rahbar A, Comstock RD, et al. Sports- and recreation-related concussions in US youth. Pediatrics 2016; 138: e20154635.
  9. Chin EY, Nelson LD, Barr WB, et al. Reliability and validity of the sport concussion assessment tool-3 (SCAT3) in high school and collegiate athletes. Am J Sports Med 2016; 44: 2276–85.
  10. Broglio SP, Katz BP, Zhao S, et al. Test-retest reliability and interpretation of common concussion assessment tools: findings from the NCAA-DoD care consortium. Sports Med 2018; 48: 1255–68.
  11. National Collegiate Athletic Association (NCAA). Interassociation consensus: diagnosis and management of sport-related concussion best practices. Indianapolis, IN, 2016.
  12. Garcia GP, Broglio SP, Lavieri MS, et al. Quantifying the value of multidimensional assessment models for acute concussion: An analysis of data from the NCAA-DoD care consortium. Sports Med 2018; 48: 1739–49.
  13. McCrea M, Guskiewicz K, Randolph C, et al. Incidence, clinical course, and predictors of prolonged recovery time following sport-related concussion in high school and college athletes. J Int Neuropsychol Soc 2013; 19: 22–33.
  14. Zemek R, Barrowman N, Freedman SB, et al. Clinical risk score for persistent postconcussion symptoms among children with acute concussion in the ED. JAMA 2016; 315: 1014–25.
  15. Iverson GL, Gardner AJ, Terry DP, et al. Predictors of clinical recovery from concussion: a systematic review. Br J Sports Med 2017; 51: 941–8.
  16. Griesbach GS, Hovda DA, Molteni R, et al. Voluntary exercise following traumatic brain injury: brain-derived neurotrophic factor upregulation and recovery of function. Neuroscience 2004; 125: 129–39.
  17. Mychasiuk R, Hehar H, Ma I, et al. Reducing the time interval between concussion and voluntary exercise restores motor impairment, short-term memory, and alterations to gene expression. Eur J Neurosci 2016; 44: 2407–17.
  18. Thomas DG, Apps JN, Hoffmann RG, et al. Benefits of strict rest after acute concussion: a randomized controlled trial. Pediatrics 2015; 135: 213–23.
  19. Leddy JJ, Kozlowski K, Fung M, et al. Regulatory and autoregulatory physiological dysfunction as a primary characteristic of post concussion syndrome: implications for treatment. NeuroRehabilitation 2007; 22: 199–205.
  20. Lawrence DW, Richards D, Comper P, et al. Earlier time to aerobic exercise is associated with faster recovery following acute sport concussion. PLoS One 2018; 13: e0196062.
  21. Leddy JJ, Haider MN, Hinds AL, et al. A Preliminary Study of the Effect of Early Aerobic Exercise Treatment for Sport-Related Concussion in Males. Clin J Sport Med. In Press. 2018: 1.
  22. Leddy JJ, Haider MN, Ellis M, et al. Exercise is medicine for concussion. Curr Sports Med Rep 2018; 17: 262–70.
  23. Schneider KJ, Meeuwisse WH, Nettel-Aguirre A, et al. Cervicovestibular rehabilitation in sport-related concussion: a randomised controlled trial. Br J Sports Med 2014; 48: 1294–8.
  24. Hugentobler JA, Vegh M, Janiszewski B, et al. Physical therapy intervention strategies for patients with prolonged mild traumatic brain injury symptoms: A case series. Int J Sports Phys Ther 2015; 10: 676–89.
  25. Schmidt JD, Hoffman NL, Ranchet M, et al. Driving after concussion: Is it safe to drive after symptoms resolve? J Neurotrauma 2017; 34: 1571–8.
  26. Asken BM, Bauer RM, Guskiewicz KM, et al. Immediate removal from activity after sport-related concussion is associated with shorter clinical recovery and less severe symptoms in collegiate student-athletes. Am J Sports Med 2018; 46: 1465–74.
  27. McCrea M, Guskiewicz K, Randolph C, et al. Effects of a symptom-free waiting period on clinical outcome and risk of reinjury after sport-related concussion. Neurosurgery 2009; 65: 876–83.
  28. Brooks MA, Peterson K, Biese K, et al. Concussion increases odds of sustaining a lower extremity musculoskeletal injury after return to play among collegiate athletes. Am J Sports Med 2016; 44: 742–7.
  29. Kerr ZY, Evenson KR, Rosamond WD, et al. Association between concussion and mental health in former collegiate athletes. Inj Epidemiol 2014; 1: 28.
  30. Asken BM, Sullan MJ, DeKosky ST, et al. Research gaps and controversies in chronic traumatic encephalopathy: A review. JAMA Neurol 2017; 74: 1255–62.
  31. Asken BM, Sullan MJ, Snyder AR, et al. Factors influencing clinical correlates of Chronic Traumatic Encephalopathy (CTE): a Review. Neuropsychol Rev 2016; 26: 340–63.
  32. Black AM, Macpherson AK, Hagel BE, et al. Policy change eliminating body checking in non-elite ice hockey leads to a threefold reduction in injury and concussion risk in 11- and 12-year-old players. Br J Sports Med 2016; 50: 55–61.
  33. Kerr ZY, Yeargin SW, Valovich McLeod TC, et al. Comprehensive coach education reduces head impact exposure in american youth football. Orthop J Sports Med 2015; 3: 232596711561054.
  34. Emery CA, Black AM, Kolstad A, et al. What strategies can be used to effectively reduce the risk of concussion in sport? A systematic review. Br J Sports Med 2017; 51: 978–84.