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Sport related concussion (SRC) in the broadest terms is defined as the immediate and transient symptoms of traumatic brain injury.1 It is more specifically defined as a traumatically induced transient disturbance of brain function that involves a complex pathophysiological process) that cannot be explained by structural injury on standard brain imaging, drugs, alcohol, or other underlying comorbidities.2


SRC may result from either a direct impact to the head, or an impact elsewhere in the body, which can lead to an impulsive force transmitted to the head and brain. 1

Epidemiology including risk factors and primary prevention

There are an estimated 1.7-3.8 million sport-related concussions in the U.S. each year, with the true incidence remaining unknown due to the likelihood of underreported cases due to nondisclosure by athletes and variability in symptomatology.3 In fact, studies demonstrate that up to 50% of concussions may go unreported.8,9,10 To reinforce the large age discrepancy amongst SRC, Bryan et al. report 1.1 to 1.9 million SRC occur annually in US children aged ≤18 years.4 The data suggest a trend of increased annual concussion rates over the past decade, which is speculated to be a result of the emphasis on concussion education and awareness leading to increased identification and reporting.5,6,7 Sports with the highest risk appear to be football, soccer, ice hockey, and lacrosse.11,12,13 There are reported gender differences as soccer and basketball demonstrated a significantly higher incidence of concussions in females compared with males.14 Other factors that may influence SRC susceptibility include history of prior concussion, initial symptoms and their severity, history of migraines, and premorbid psychiatric conditions which include learning disorders and ADHD.14 History of a previous concussion is a clear risk factor.15


The pathophysiology of concussion is theorized to be secondary to disruptive stretching of neuronal cell membranes after a direct or indirect head trauma.1 This neuronal damage leads to intracellular ionic shifts and mitochondrial dysfunction that results in subsequent reactive oxygen species and an increase in glucose metabolism, to restore the homeostasis of sodium and potassium within the cell.16

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

The onset of symptoms following a concussion can be immediate or within minutes after the initial impact. The most common reported symptoms are headache and dizziness. Acutely, the athlete may also describe a feeling of fogginess, complain of tinnitus, confusion, flashing lights, nausea, or amnesia. Other commonly reported symptoms are sensitivity to bright lights, altered sleep patterns, poor concentration, and irritability. In addition, an athlete may notice increasing fatigue and delayed reaction time with physical and mental tasks. Long-term effects might include neurobehavioral or cognitive impairments.1,2

Following a SRC, there is typically a gradual reduction in symptoms. The majority of concussive symptoms resolve within 7 to 10 days, but some cases may evolve to post-concussive syndrome (PCS) through a process that is poorly understood. PCS should be suspected if there is failure of clinical recovery, defined by symptoms lasting >10–14 days in adults and >4 weeks in children.1

Specific secondary or associated conditions and complications

Complications of a concussion in the absence of other significant medical diagnoses or injuries are usually related to cognitive impairments. The athlete may experience insomnia, emotional lability, memory impairments, depression, anxiety, fatigue, headache, and/or dizziness.1

Essentials of Assessment


It is essential to understand that direct head trauma is not necessary for a concussion to occur. The goal of the sideline evaluation is to screen for suspected SRC and determine disposition. After a suspected concussion, the athlete should be immediately removed from play to be assessed and examined. Ideally, the injury is witnessed by the covering physician or other medical professional on the field who can describe the mechanism and identify immediate signs of injury, trauma, or LOC. A graded symptoms checklist (GCS) and Sports Concussion Assessment Tool (SCAT) provide devices for the initial assessment and tracking of symptoms over subsequent evaluations, which will be further discussed in the “Functional Assessments” section. The Center for Disease Control’s Heads Up Concussion Signs and Symptoms Checklist provides four domains:

  1. Observed signs (e.g., LOC, posttraumatic amnesia),
  2. Physical symptoms (e.g., headaches, nausea committing),
  3. Cognitive symptoms (e.g., feeling foggy, “does not feel right”), and
  4. Emotional symptoms (e.g., irritable, sad, more emotional).17

The athlete may not be able to recall the incident, thus spectators may need to be questioned or game tapes reviewed.

Physical examination

Initially, the on-field examination should focus on evaluating for emergent injuries and symptoms. Red flag symptoms that, at the minimum, require removal from play include neck pain or tenderness, paresthesias, worsening headache, LOC, convulsion, vomiting, worsening confusion, or deteriorating consciousness.2,18 The cervical spine, skull, and facial bones need to be palpated for any evidence of fracture. If the athlete is stable the remainder of the examination may be performed on the sideline. If the athlete is unstable, immediate hospital transport for stabilization and further evaluation is necessary. A thorough neurological evaluation needs to be performed that includes cranial nerves, sensation, strength, coordination, balance, and cognition.

Functional assessment

Functional assessment of the concussed athlete includes a thorough neuromuscular and cognitive evaluation. Standardized assessment tools are available, and they are designed to reduce the degree of subjectivity encountered by medical providers responsible for making a rapid and precise injury assessment and concussion diagnosis decision. When possible, tests can be compared to a reliable pre-injury baseline.2 The primary endpoint for sideline assessment in suspected athletes with SRC is to determine the probability that an athlete has sustained a concussion. If there is definite or probable evidence of concussion, then the athlete should be removed from competition and serially assessed.

The Sports Concussion Assessment Tool 5th edition (SCAT5) is most commonly utilized in practice, and it incorporates a neurological assessment that includes tandem gait testing, concentration, modified Balance Error Scoring System (mBESS) testing, and delayed recall after using either a 5 or 10-word list assessed after 5 minutes.18 The mBESS is used to assess postural stability to test for objective neurologic functioning.19 An abbreviated version of the SCAT5 is typically performed on the sidelines, with the full assessment to be performed subsequently in a distraction-free environment.

The Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) is another assessment tool. This 20-25 minute computer based assessment uses a baseline assessment and in the event of a SRC, a post-injury test is used to help aid in the diagnosis of an SRC. Athletes are generally not allowed to return to play until the post-injury scores are closer to baseline, but that is up to the discretion of the healthcare professional.20

The Vestibular Ocular Motor Screening (VOMS) tool is another tool used by practitioners that allows for a standardized method of assessing vestibular-ocular function. It uses 5 domains: 1) smooth pursuit, 2) horizontal and vertical saccades, 3) near point of convergence distance, 4) horizontal vestibular ocular reflex, and 5) visual motion sensitivity.21

Another unique assessment in SRC is reaction time using a dropped weighted and metered stick. The examiner drops the stick between the athlete’s open hand, who must catch it. Eckner et al. found that reaction time appears to decipher between concussed and non-concussed athletes similarly when compared to other concussion tools.22

The athlete will often have cognitive deficits after sustaining an SRC. The length of the deficits can be highly variable. Concentration, attention, mood, and sleep can be affected, which can further impact school, work, and daily activities. The athlete’s school performance should be closely followed after a SRC. A comprehensive neuropsychological evaluation can be used to identify subtle cognitive deficits as cognitive recovery may either come before or after clinical symptom resolution .1,2

Further description of standardized assessment tools will be discussed below under “Supplemental Assessments Tools”. Of note, repeat annual baseline testing after an initial baseline evaluation is no longer recommended for collegiate athletes.23

Laboratory studies

There are currently no recommendations for laboratory studies directly related to an SRC. As SRC remains largely a clinical diagnosis, there is a desire to uncover biochemical and genetic markers that can assist with diagnosis, prognosis, and recovery monitoring. Studies are underway to evaluate the roles of cytokine IL-6, IL-1, apolipoprotein E, S100 calcium-binding protein B, salivary microRNA markers, and neurofilament light chain in serum or CSF.24,25 In 2018, the FDA approved the use of the Brain Trauma Indicator, a serum test for measuring the probability of an intracranial lesion that would necessitate further imaging; the biomarkers involved are ubiquitin carboxy-terminal hydrolase-L1 (UCH-L1) and glial fibrillary acid protein (GFAP).26


Traditional neuroimaging (i.e., CT or MRI) is normal immediately following a SRC. It is reserved for patients with suspected intracranial pathology as evidenced by findings of worsening mental status, declining level of consciousness, focal neurological deficits, seizures, intractable vomiting, anisocoria, rhinorrhea, or otorrhea. There is recent interest in advanced MRI techniques such diffusion tensor imaging (DTI) to serve as imaging biomarkers of microstructural change, even to the extent that they may distinguish between concussive and subconcussive injuries. Although imaging is not required to diagnose SRC as it is a functional injury, evidence of structural injury would modify the diagnosis to TBI. For the purpose of research, the use of DTI and functional MRI may offer a tool with which one can monitor recovery after a concussion.

Supplemental assessment tools

While there is no standard, the SCAT5 is the most widely utilized tool for evaluating concussions on the field and, if done prior to play, as a measure to compare pre- and post-injury baseline. The SCAT5 consists of 2 locations of interview 1) on the field and 2) in the clinician’s office after the injury. The on-field assessment includes 5 general steps: 1) red flag symptoms, 2) observable signs, 3) memory assessment using Maddocks’ questions, 4) Glasgow Coma Scale, and 5) cervical spine assessment. The clinical evaluation is a more thorough 6 step assessment that includes a cognitive assessment and extensive symptom evaluation. The symptom evaluation component may be particularly helpful in tracking recovery.1,2

Another tool used is the King–Devick (KD) test. The KD test is a 2-minute sideline assessment of rapid number naming and vision assessment where the athlete reads numbers on three cards. This requires eye movements, language function and attention – all of which are usually affected in SRC.28 The KD test is easy to perform and has high sensitivity and specificity; however, the recommendation remains that it be used in conjunction with the SCAT5 to diagnose a SRC.29

Baseline testing pre-injury may help identify SRC in the athlete, but is not routinely performed, nor is it fully supported in the literature. Of the neurocognitive tools, the one that shows the greatest benefit from baseline testing is the KD test, as it evaluates more individualized cognitive processes that are expected to be altered in concussion.29,30

Early predictions of outcomes

Early predictions of outcomes continue to be an area of evolving research that may help in identifying more vulnerable populations after SRC, especially as SRC-related morbidity typically occurs in the first weeks to months following injury. Iverson et al. described 5 relationships that are commonly asked and are of significant clinical relevance:

  • The relationship between age and clinical recovery: The authors report that professional athletes may have a faster recovery when compared to amateur athletes. Moreover, the rate of those affected by SRC that continue to have symptoms past 4 weeks are 5–7 year-olds = 17.9%, 8–12 year-olds = 26.3% and 13–17 year-olds = 39.9% indicating that older children may have longer recovery times. Interestingly, this discrepancy may arise from the ability of older children to communicate more succinctly than younger children who cannot because of the normal intellectual differences between a 17-year-old and a 7-year-old.
  • The relationship between sex and clinical recovery: After a SRC, females tend to take longer to recover and have more persistent symptoms > 4 weeks. This discrepancy is multifactorial and continues to require further research.
  • The relationship between history of concussion and clinical recovery: After an athlete has sustained an initial SRC, they are more likely to have a second SRC. Those who have sustained a first SRC will have higher pre-injury symptoms prior to their second SRC. More research is needed in this area, but there is research to suggest that history of concussions may result in symptoms lasting greater than 4 weeks.
  • Relationship between neurodevelopmental disorders, mental health, migraine and clinical recovery: This is a unique population as children with neurodevelopmental disorders, such as ADHD and learning disabilities, report more concussion symptoms without ever having a SRC, thus their pre-injury scores may be unreliable. Pre-morbid depression and migraine may also prolong recovery with symptoms lasting greater than 4 weeks. 31 However, a recent study found that ADHD medication usage is associated with a shorter return to play.38
  • Relationship between surrogate measures of injury severity and clinical recovery: LOC, retrograde amnesia, and post-traumatic amnesia are not consistent or strong predictors of recovery. The strongest predictor of longer recovery time is severity of the acute and sub-acute symptom burden after the SRC.31

Social role and social support system

Individuals may notice that attempting tasks in the home and at work/school often increase their concussive symptoms. For student athletes, teachers need to have the understanding that they may need additional time with homework or testing due to problems with attention and concentration. Cognitive rest is very important in the acute recovery from a concussion, and includes restrictions on cell phone use, texting, video games, physical activity and schoolwork until symptoms abate.

Some athletes experience mental health-related consequences including anxiety, depression and sleep disturbances. Contributing factors may include frustration over uncertain recovery time, isolation from teammates and sport and lack of social support. Prior to pharmacologic or psychotherapy, treatment involves behavioral management interventions, such as regulated sleep schedule, proper nutrition and stress reduction.1.2 There are studies which  suggest a direct correlation between the number of SRCs and mental health related symptoms; and that severity of those symptoms tends to be greater in those patients with PCS.32,33 As management of SRC requires an interdisciplinary approach, this highlights the importance of patients’ getting appropriate psychological care.

Professional issues

If athletes are returned to play prior to full cognitive and physical recovery they are at risk for worsening symptoms, prolonged recovery and an increased risk of suffering additional concussions. “Second impact syndrome” is a potentially life-threatening and catastrophic injury, resulting from a second concussion where the athlete never fully recovered from the first concussion.2 Concussion legislation emerged in this country after the state of Washington passed the Lystedt Law in 2009 in response to a case of a football player suffering a severe brain injury after returning to play during the same game in which he suffered a concussion. The law requires athletes to be removed immediately from athletic activities if it is suspected they have sustained a concussion. Within 5 years, all 50 states have passed a similar law.34 In order to return to play, athletes must be evaluated and receive written clearance from a health care provider trained in concussion assessment.

Rehabilitation Management and Treatments

The rehabilitation of concussion evolved out of the 5th Consensus Statement in Berlin which was published by the Concussion in Sports Group (CISG). Rehabilitation is now considered part of the mainstay in SRC treatment, with emphasis placed on balance control and cognitive function.

Following immediate removal from play, a physical and cognitive rest period of 24-48 hours is recommended. Patients can then undergo gradual return to activity, including return to school and return to play. 1

Activity and exercise intolerance may result from impaired autonomic regulation. As such, it is important to increase activity at a sub-symptom threshold.2 The Buffalo Concussion Exercise Treatment Protocol, which is a progressive, sub-symptom threshold, aerobic exercise program monitors cardiac status and symptoms using the Buffalo Concussion Treadmill Test. Early studies suggested this protocol could indicate readiness to start a graded return to sport protocol.35 A systematic review by Reid et al. further examined the role of subthreshold aerobic exercise in SRC patients and concluded that it led to lower symptom scores but did not reduce the time to recovery.36

Return to learn is the transition back to school and the classroom. It is important to keep an open line of communication with professors, teachers and school administrators as to the student-athlete’s recent injury. Although most student athletes recover quickly some with persistent symptoms may require more time to complete schoolwork which will require accommodations. The protocol for return to learn as outlined by CISG is as follows: 1) ADLs with light cognitive activity outside of the classroom, 2) school-related cognitive activities outside the classroom, 3) part-time return to school and 4) full time return to school.

Return to sport (RTS) should progress in an individualized manner based on the athlete’s injury, age and level of play. For student-athletes, a return to the classroom takes precedence.2 The CISG suggests a 6 stage RTS protocol which includes: 1) symptom limited activities of daily living, 2) light aerobic exercise, 3) sports specific exercise, 4) non-contact drills, 5) full-contact drills, and 6) return to sport. Each stage should allow for 24 hours of symptom free activity. If the patient becomes symptomatic at any stage, the activity is stopped for the day and, upon symptom resolution, the patient may start at the previously asymptomatic stage the following day.1 Interestingly, return to sport takes more of an empiric approach rather than evidence-based approach as there are limited data to support how long an athlete should remain in each stage.2,37 A recent study by Broglio et al. suggests that the normal recovery window may extend up to 1 month.38

There is significantly limited data on return to driving and no guidelines currently exist for those patients passing the symptom-free 24-48 hours of recommended physical and cognitive rest.2 The general practice is to provide individualized patient education and tips for slow progression such as utilizing others means of transport, driving when traffic is minimal, limiting distractions while driving and avoiding driving when fatigued.39

At different disease stages

As previously described, most concussions and sequelae resolve within 2 weeks for adults and 4 weeks for adolescents and children.21 It is important to keep in mind that clinical recovery may not correlate with physiologic recovery.21 Treatment of SRC has remained controversial, but clearer clinical guidelines are emerging. Prolonged total physical and cognitive rest is no longer recommended. Consensus guidelines now endorse 24-48 hours of symptom-limited cognitive and physical rest, followed by gradual increase in activity as long as the athlete remains symptom free throughout the progression.1,2 As per the consensus statement in Berlin, treatment should be individualized, including a symptom-limited aerobic exercise program, targeted physical therapy program, and a multidisciplinary approach including neuropsychology and cognitive behavioral therapy.1

Coordination of care

The approach to an athlete with a SRC should integrate multiple disciplines. A physician familiar with SRC should be directing care and decisions, often involving collaboration with physical/occupational therapists and neuropsychologists. Additionally, athletic trainers, family, coaching staff, teachers and friends are integral in the well-being of the athlete.

Patient & family education

The athlete, family, friends, teachers and coaches need to be educated on the effects of SRC. There needs to be an understanding of the injury in order to protect the athlete and support him/her through the recovery process.39

Emerging/unique interventions

Neuropsychological testing is used to evaluate cognitive impairment. Newer forms of testing utilizing computer-based programs are simple and sensitive but are not substitutes for formal neuropsychological batteries.1 These computerized tests evaluate an athlete’s visual memory, verbal memory, processing speed and reaction time and can follow the resolution of cognitive deficits with serial testing.2,21 Although there is insufficient evidence to recommend the widespread use of baseline neuropsychological testing, this may be more important in high-risk athletes with a prior history of concussion, confounding conditions (learning disability, mood and attention disorders, migraine headaches) or those in high-risk sports.1,2

There are some reports of herbal medicine therapies and supplements having neuroprotective properties.40 Furthermore, certain vitamins and supplements (e.g., vitamins C, D, E, omega-3 fatty acids, melatonin, curcumin, creatine) have been shown to aid in the recovery of patients with concussion. Other alternative therapies, such as acupuncture, acupressure and music therapy, may also aid in helping patients with residual symptoms.40

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Concussion is a clinical diagnosis; neither a normal physical examination nor standardized test (e.g., SCAT5) will rule out concussion. As such, clinicians must use their judgment and consider the whole clinical picture. One of the most important aspects of SRC recovery is the removal of athletes from play. There are many useful tools for monitoring symptom resolution and cognition recovery to inform the clinician on an individual athlete’s readiness to return to play that were discussed.  Return to sport should progress in an individualized manner based on the athlete’s injury, age, history and level of play. Most athletes >18 years old recover within 10-14 days while athletes <18 years old are expected to return back to baseline cognitive and athletic function in <4 weeks. For student athletes, it is generally recommended that a return to full, unrestricted school precede a return to sport.41

Cutting Edge/ Emerging and Unique Concepts and Practice

There is increasing concern that recurrent concussions contribute to long-term impairment. Some studies have suggested an association between previous concussions and chronic cognitive dysfunction.2 Others have reported that SRC might lead to long term mental health symptoms in former athletes.42 Chronic Traumatic Encephalopathy (CTE) represents an interesting and unique entity in concussion research. Its incidence and prevalence are unknown. A cause and effect relationship between postmortem CTE changes and antemortem behavioral and cognitive manifestations has not been demonstrated. It is also unknown if CTE is a progressive disease, and if tau deposition is a cause, byproduct, or marker.1,2

New, emerging treatments for concussion include high dose omega-3 fatty acids, Vitamin D, progesterone, N-methyl-D-aspartate, and ketogenic diets. Currently, all studies are inconclusive, but research is continuing in those areas.

Another interesting, but not yet validated tool, are helmet monitors. These monitors allow for sensors to monitor linear and angular acceleration forces to the brain. A limitation of the monitors is that some athletes experience high forces with no resultant concussion, while others have lower impact forces with concussion. 2

Imaging, such as CT and MRI, are usually not necessary in concussion workup unless there is concern for intracranial bleeding or there is prolonged recovery. Newer, advanced MRI technologies, including diffusion tensor imaging, resting state functional MRI, arterial spin labeling, are being actively researched.

Fluid biomarkers, including those found in blood, saliva, and cerebrospinal fluid, are also being investigated. More recently in 2018, the Federal Drug Administration approved biomarkers for the diagnosis of TBI. The biomarkers approved were ubiquitin carboxy-terminal hydrolase L1 and glial fibrillar acidic protein in patients with Glasgow scores from 9-15.37 There are currently no SRC-specific tests to recommend.2

As previously mentioned, activity and exercise are currently being evaluated to establish a more definitive protocol for athletes to return to play, but clear protocols and guidelines still require more research.

Gaps in the Evidence-Based Knowledge

One of the major questions in SRC research is determining when an athlete should retire from sport after multiple concussions. Limited data is available, and more research is needed on sub-concussive impacts and neurological health. There are currently no evidenced-based guidelines on retiring athletes from their sport based on the number of concussions sustained.1,2 One publication recommends that health care providers review with athletes a series of questions that can help guide the retirement discussion, which include whether there is a reduced threshold for injury, persistent injury effects, abnormal findings on neuroimaging and the potential risks and benefits of continued participation.After these questions are asked, information should be provided to the athlete and options can be considered prior to making a shared decision.43

Further study on objective neuroimaging techniques and fluid biomarkers are needed for both assessing SRCs, as well as identifying factors that may prolong recovery. Nutraceuticals are another domain in SRC research that is evolving but still lack a clear evidence-based foundation.2

Additional research is needed to validate current assessment tools, further delineate the role of neuropsychologic and balance testing, validate return-to-play guidelines and improve identification of those at risk for prolonged concussive symptoms. Large-scale, epidemiological studies are needed to clearly define risk factors and causation of long-term neurological impairment, as well as establishing prevalence and incidence in amateur and professional athletes with SRC.2


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Original Version of the Topic:

Ken Mautner, MD, Matthew Axtman, DO. Sports Concussion. 11/15/2011.

Previous Revision(s) of the Topic

Timothy Tiu, MD , Rakhi Sutaria MD, Se Won Lee, MD. Sports Concussion. 5/5/2016.

Timothy Tiu, MD, Armando Alvarez MD, MPH. Sports Concussion. 7/31/2020

Author Disclosure

Timothy Tiu, MD
Nothing to Disclose

Sandra De Mel, MD
Nothing to Disclose

Edwin Amirianfar, DO
Nothing to Disclose