Understanding Concussion Biomechanics and Pathophysiology

A concussion is a mild traumatic brain injury (mTBI) caused by a direct blow to the head, face, or neck, or a blow elsewhere on the body that transmits an impulsive force to the head. In contact sports like football, hockey, rugby, and soccer, the most common mechanisms involve head-to-head collisions, head-to-ground impacts, or whiplash-type motion from a tackle. The resulting acceleration–deceleration forces cause the brain to move within the skull, leading to shearing of axons, disruption of neuronal membranes, and a cascade of cellular events known as the neurometabolic cascade.

Key elements of this cascade include potassium efflux, calcium influx, release of excitatory neurotransmitters (e.g., glutamate), and an increased demand for adenosine triphosphate (ATP). The brain enters a state of energy crisis because mitochondrial function is impaired. This mismatch between energy supply and demand makes the brain vulnerable to further injury and explains why symptomatic athletes are at higher risk for a second, potentially catastrophic concussion if returned to play too soon. Recovery involves gradually restoring ionic balance and normal energy metabolism, which typically takes days to weeks but can be prolonged in some cases. Understanding this biology reinforces why immediate removal from play and relative rest are non-negotiable first steps.

For a deeper dive into the molecular mechanisms, the CDC’s Heads Up initiative provides accessible explanations and clinical resources.

Recognizing Common and Atypical Symptoms

Concussion symptoms are highly individualized and can evolve over minutes, hours, or even days after the impact. The ability to recognize both typical and less common signs is critical for sideline staff and medical personnel. Classic symptom clusters include:

  • Somatic symptoms: headache (most common), dizziness, visual disturbances (e.g., blurry vision, sensitivity to light), nausea, imbalance, and neck pain.
  • Cognitive symptoms: feeling mentally foggy, difficulty concentrating, memory lapses (especially retrograde and anterograde), slowed reaction time, and feeling “in a daze.”
  • Emotional and behavioral changes: irritability, sadness, anxiety, mood swings, and emotional lability.
  • Sleep disturbances: drowsiness, sleeping more than usual, insomnia, or difficulty falling asleep.

Less commonly recognized but important symptoms include tinnitus (ringing in the ears), phonophobia (noise sensitivity), photophobia (light sensitivity), changes in taste or smell, and a sense of “just not feeling right.” Athletes may also report neck pain or headaches that radiate from the cervical spine, which can mimic concussion symptoms. Because many athletes underreport to avoid being pulled from competition, coaches and trainers must maintain a high index of suspicion. The Consensus Statement on Concussion in Sport emphasizes that any suspected concussion should be treated as a concussion until proven otherwise.

Red Flags Requiring Emergency Evaluation

Certain signs and symptoms indicate a more severe brain injury, such as a subdural hematoma or diffuse axonal injury, and warrant immediate transport to an emergency department with neuroimaging capability. These red flags include:

  • Loss of consciousness lasting more than 30 seconds
  • Worsening headache or a severe headache at onset
  • Repeated vomiting or protracted nausea
  • Seizure or convulsion (including a brief impact seizure)
  • Focal neurological deficits (e.g., weakness or numbness in one limb, slurred speech, facial droop, unequal pupils)
  • Increasing confusion, agitation, or declining level of consciousness
  • Double vision or cranial nerve palsy
  • Amnesia for more than 30 minutes

Any athlete exhibiting one or more red flags should be treated as a medical emergency. Sideline staff should activate emergency medical services and avoid moving the athlete unless necessary to protect the airway.

Immediate Sideline Assessment and Removal From Play

The golden rule of concussion management is “when in doubt, sit them out.” Any athlete suspected of having a concussion must be removed from practice or competition immediately and not returned to play that same day, regardless of how quickly symptoms appear to resolve. A standardized sideline assessment tool, such as the Sport Concussion Assessment Tool 5 (SCAT5) or the Child SCAT5 for athletes under 13, provides a structured framework for documenting the injury and guiding referral.

Key Components of the Sideline Exam

  • Observation for visible signs: lack of coordination, vacant stare, slow response to questions, loss of consciousness, impact seizure, or motor incoordination.
  • Orientation questions: “What happened?” “Where are we?” “What period/quarter is it?” “Who are we playing?”
  • Maddocks questions: A brief set of sideline cognitive screening questions (e.g., “Which half is it?” “Who scored last?”).
  • Balance assessment: Modified Balance Error Scoring System (BESS) — tandem stance, single-leg stance, and double-leg stance on a firm surface.
  • Cervical spine screen: If the mechanism involves high velocity or neck pain, perform a brief cervical spine exam before moving the athlete.

The SCAT5 is not a diagnostic tool but a standardized method to document the athlete’s condition at the time of injury. It should be used alongside clinical judgment. Whenever possible, a trained health professional (athletic trainer, team physician) should conduct the assessment. For the full protocol, consult the SCAT5 guidelines.

Initial Management: Physical and Cognitive Rest

In the first 24–48 hours after injury, the priority is relative rest to allow the brain to recover its energy balance. The term “relative rest” means reducing activities that demand significant mental or physical energy, but complete isolation (e.g., dark room, no stimulation) is no longer recommended beyond the first day or two. Strict rest beyond 48 hours can lead to deconditioning, mood disturbances, and even delayed recovery.

Recommended activities during the acute phase include:

  • Light walking or gentle stretching, as long as it does not exacerbate symptoms
  • Listening to podcasts or music at a low volume (if no phonophobia)
  • Short periods of screen time for essential communications, with frequent breaks
  • Maintaining sleep hygiene: consistent wake/sleep schedule, avoiding caffeine and screens 60 minutes before bed, keeping the room cool and dark

Activities to avoid include strenuous exercise (running, lifting, competitive sports), prolonged reading, bright or flashing lights, loud environments (concerts, crowded rooms), and demanding cognitive tasks (work, school assignments, complex video games). Athletes should also avoid driving while symptomatic, especially if they experience dizziness or visual disturbances.

Academic accommodations (e.g., reduced workload, extended deadlines, rest breaks during class) should be arranged early, particularly for student-athletes. The goal is to find the “symptom threshold” — the level of activity that does not worsen symptoms — and then gradually expand activity within that boundary.

Multidisciplinary Approach to Concussion Management

Concussion recovery often involves multiple body systems (neurologic, vestibular, ocular, cervical, psychological), and optimal outcomes require a collaborative team. A well-structured concussion program may include:

  • Primary care physician or sports medicine specialist: Oversees overall care, performs a comprehensive neurologic exam, determines need for neuroimaging, provides clearance for return-to-play progression.
  • Neuropsychologist: Administers and interprets objective cognitive testing (e.g., ImPACT, CNS Vital Signs, or ANAM) to track recovery and guide return to school or work.
  • Vestibular therapist: Assesses and treats dizziness, balance deficits, gaze instability, and motion sensitivity using targeted exercises.
  • Physical therapist: Addresses cervical spine dysfunction (common after whiplash-type mechanisms), cervicogenic headache, and exercise intolerance through graded aerobic exercise.
  • Neuro-optometrist or vision therapist: Evaluates convergence insufficiency, accommodative dysfunction, saccadic abnormalities, and other vision problems that can cause persistent headaches and reading difficulties.
  • Certified athletic trainer: Provides day-to-day symptom monitoring, communicates with coaches and parents, and implements the return-to-play protocol.
  • Mental health professional: Helps manage anxiety, depression, or frustration that often accompanies a concussion, especially when recovery is prolonged.

This biopsychosocial model addresses all contributors to symptoms and reduces the risk of persistent post-concussion symptoms. Many sports organizations now partner with multidisciplinary concussion clinics. The BrainLine.org resource offers a directory of services and educational materials for families and clinicians.

Gradual Return-to-Play Protocol

Once the athlete is symptom-free at rest and has been cleared by a physician, a stepwise return-to-play (GRTP) protocol should begin. The six-stage approach recommended by the International Conference on Concussion in Sport ensures that the athlete can tolerate increasing physical demands without symptom recurrence. Each stage requires at least 24 hours of asymptomatic activity before progressing.

The Six Stages

  1. Stage 1: Symptom-limited activity. Daily activities that do not provoke symptoms (e.g., walking to class, light household chores). No structured exercise.
  2. Stage 2: Light aerobic exercise. 15–20 minutes of walking or stationary cycling at 55–70% maximum heart rate. No resistance training. If no symptoms, proceed after 24 hours.
  3. Stage 3: Sport-specific exercise. Running drills, skating maneuvers, passing drills — activities that mimic the sport but without head impact or contact.
  4. Stage 4: Non-contact training drills. Higher intensity, more complex drills, including resistance training, agility work, and sport-specific movements. Still no contact.
  5. Stage 5: Full contact practice. Athlete participates in regular practice after medical clearance. Important to monitor for any delayed symptoms.
  6. Stage 6: Return to competition. Athlete is cleared for game play.

If symptoms recur at any stage, the athlete should drop back to the previous asymptomatic stage, rest for 24 hours, and then attempt progression again. Individual timelines vary widely, and some athletes may need longer windows between stages. Regression should trigger a medical reassessment.

It is critical to note that return-to-play should not begin until the athlete has successfully completed a return-to-learn protocol (i.e., is tolerating full academic workload without accommodations). The brain must first recover its cognitive capacity before it can handle the physical demands of sport.

The Role of Baseline Testing and Multimodal Assessment

Baseline neurocognitive testing (e.g., ImPACT, CogSport, or the Standardized Assessment of Concussion) is widely used in collegiate and professional settings to establish an athlete’s pre-injury cognitive performance. After a concussion, scores are compared to baseline to help determine when cognitive function has returned to normal. However, baseline testing has notable limitations: it can be affected by effort, environmental distractions, and practice effects. Moreover, not all athletes have reliable baselines due to suboptimal testing conditions or lack of testing altogether.

Therefore, baseline testing should be used as one component of a comprehensive assessment that also includes symptom checklists, balance testing, and the Vestibular/Ocular Motor Screening (VOMS). The VOMS tool assesses five domains: smooth pursuits, saccades, convergence, vestibular-ocular reflex, and visual motion sensitivity. It is quick (5–10 minutes) and can identify impairments that are common after concussion and often missed by standard exams. Athletes with abnormal VOMS scores may benefit from early referral to a vestibular therapist, which can speed recovery.

Managing Prolonged Concussion Symptoms

Approximately 10–15% of athletes experience symptoms that persist beyond three months, defined as persistent post-concussion symptoms (PPCS). Risk factors include pre-existing anxiety or depression, a history of migraines, female sex (due to neck strength and hormonal factors), younger age, and multiple prior concussions. Management of PPCS requires a more comprehensive, individualized approach that goes beyond simple rest.

  • Sub-symptom threshold aerobic exercise: Daily walking or stationary cycling at a heart rate below the level that triggers symptoms can improve cerebral blood flow and promote recovery. This should be supervised by a physical therapist or athletic trainer.
  • Cervical spine physical therapy: Many persistent headaches and dizziness after concussion originate from the neck. Manual therapy, stretching, and strengthening of the cervical muscles can be highly effective.
  • Vestibular rehabilitation: For balance problems, gaze instability, and motion sensitivity, specific exercises like gaze stabilization, habituation, and balance training are indicated.
  • Cognitive behavioral therapy (CBT): Helps athletes manage anxiety, catastrophizing, and mood disturbances that often accompany prolonged recovery.
  • Vision therapy: For convergence insufficiency, accommodative spasm, or other oculomotor dysfunctions, structured vision exercises can reduce eye strain and headaches.
  • Academic and occupational accommodations: Gradual return to school or work with reduced hours, extended deadlines, rest breaks, and a quiet environment.

Pharmacological interventions (e.g., amantadine for cognitive symptoms, tricyclic antidepressants or topiramate for chronic headache, melatonin for sleep disruption) are generally reserved for cases that do not respond to non-pharmacologic treatments and should be prescribed by a specialist. The American Orthopaedic Society for Sports Medicine provides additional clinical guidance on managing complex concussions.

Long-Term Considerations and Prevention

Emerging evidence suggests that repetitive head impacts, even at sub-concussive levels, may be associated with chronic traumatic encephalopathy (CTE) and other neurodegenerative conditions. While not every athlete with multiple concussions develops CTE, cumulative exposure to head trauma is a significant risk factor. This underscores the critical importance of prevention and conservative management.

Preventive Strategies

  • Proper equipment and fitting: Helmets are designed to reduce skull fractures and scalp injuries but do not prevent concussion. Mouthguards protect teeth but have limited evidence for concussion reduction. Ensuring proper fit and condition of equipment is still essential.
  • Rule enforcement and policy changes: Strict officiating to eliminate targeting, head hits, and illegal checking. Many youth and high school leagues now limit full-contact practices (e.g., no more than one contact practice per week in football).
  • Education and culture change: Athletes, coaches, and parents must be educated to recognize concussion symptoms and understand the dangers of playing while symptomatic. A culture that prioritizes safety over winning reduces underreporting.
  • Neck strengthening and conditioning: Stronger neck muscles may reduce head acceleration during impact by providing better stabilization. Programs that include isometric and dynamic neck exercises are being integrated into training regimens.
  • Limiting head impact exposure: In sports like soccer, limiting heading in practice (especially for youth players) can reduce cumulative sub-concussive impacts.

Long-term monitoring of retired athletes is an area of ongoing research. Some professional sports leagues now have neurological health programs that track cognitive function over time and offer support for those with cognitive decline.

Coaches, athletic directors, and sports organizations have a duty of care to protect athletes from foreseeable harm. Failure to properly manage a concussion can lead to legal liability, and many jurisdictions have passed legislation requiring immediate removal from play and written medical clearance for return. In the United States, all 50 states have some form of concussion law (often called “return-to-play laws”). These laws typically mandate that coaches undergo concussion education, that any athlete suspected of a concussion be removed from play, and that the athlete not return until cleared by a licensed health professional.

Documentation is critical. Every assessment, symptom evaluation, and communication with parents and coaches should be recorded in writing. This includes the initial sideline assessment, any subsequent evaluations, the return-to-play progression, and clearance. Good documentation not only protects the organization legally but also ensures continuity of care if the athlete is transferred to a different medical provider.

Some governing bodies (e.g., NCAA, NFL, FIFA) have also implemented policies that mandate baseline testing for high-risk sports, limit contact practices, and require independent concussion spotters at games. These policies reflect an evolving understanding that concussion management is both a medical and an ethical priority.

Key Takeaways for Implementation

  • When in doubt, sit them out. Remove any athlete suspected of a concussion immediately and do not allow same-day return.
  • Use standardized sideline tools (SCAT5, VOMS) and combine them with a thorough multimodal assessment.
  • Prescribe relative physical and cognitive rest for 24–48 hours, then gradually reintroduce low-level activity below the symptom threshold.
  • Implement a stepwise return-to-play protocol with at least 24 hours at each stage; progress only when symptom-free.
  • Address mental health, academic needs, and cervical/vestibular issues as part of a multidisciplinary approach.
  • Educate all stakeholders — athletes, coaches, parents, officials — about the signs of concussion and the dangers of playing injured.
  • Prevent concussions through rule enforcement, proper equipment, neck conditioning, and limiting head impact exposure in practice.
  • Document everything and stay informed about legal requirements in your jurisdiction.

By adhering to these evidence-based best practices, sports organizations can protect their athletes from short-term disability and long-term brain injury while fostering a culture of safety, transparency, and performance excellence.