Concussion in sport: when in doubt, sit it out
Introduction
"It was just a knock on the head, he'll shake it off." That's probably the most dangerous sentence said on an amateur sports field every weekend.
A concussion is a mild traumatic brain injury. The word "mild" describes the absence of structural findings on imaging, not the seriousness of what's happening: there's a real functional disturbance of the brain, and returning to play too soon can have serious consequences.
Successive international guidelines — the 2023 Amsterdam consensus being the most recent — have converged on a message that fits in six words: when in doubt, sit it out.
You don't need to lose consciousness to have a concussion. Most concussions happen without blacking out.
What happens in the brain
An impact — directly to the head or transmitted through the body, with sudden acceleration or rotation — triggers a neurometabolic cascade. The balance of ions across neuronal membranes is disrupted, glutamate is released, and cells burn a lot of energy trying to restore order precisely when cerebral blood flow is reduced.
The result is a mismatch between energy demand and availability that lasts for days. That's the physiological reason a concussed brain is especially vulnerable to a second impact: the window in which the brain is fragile doesn't match the window in which the person feels unwell.
Recognizing it
Immediate red flags: remove from play and seek urgent medical assessment.
- Loss of consciousness, however brief.
- Seizures.
- Repeated vomiting.
- Confusion, disorientation or no memory of the event.
- Severe or worsening headache.
- Unequal pupils, double vision.
- Weakness, tingling or difficulty speaking.
- Markedly altered behavior or increasing drowsiness.
- Any suspicion of a neck injury.
Subtler symptoms, appearing or growing over hours:
- Headache and pressure in the head.
- Mental fog, slowness, difficulty concentrating.
- Dizziness or balance problems.
- Sensitivity to light and noise.
- Nausea.
- Unusual irritability, sadness or nervousness.
- Sleeping more or less than usual.
And one rule that prevents almost every serious error: anyone with a suspected concussion does not return to play that day, even if they say they're fine and even if symptoms seem to have gone. There's no exception for how important the game is.
The return, on two ladders
The current consensus sets out two parallel progressions, and the one for school or work comes first.
Return to learning. Absolute cognitive rest is no longer recommended beyond the first 24 to 48 hours: shutting yourself in a dark room for days delays recovery. You progress from short cognitive activities at home to a full school or work day, allowing a mild symptom increase that settles quickly.
Return to sport, in six steps. Each step takes at least 24 hours, and you only advance if symptoms don't worsen:
1. Daily activities that don't provoke symptoms. 2. Light aerobic exercise: walking, easy stationary cycling. Recent evidence supports introducing this early, within the first 48 hours, rather than waiting. 3. Sport-specific exercise with no risk of impact: running, changes of direction. 4. Non-contact training drills, with more load and complexity. 5. Full contact practice, after medical clearance. 6. Return to competition.
If symptoms return at any step, you go back to the previous one and wait at least 24 hours.
Groups requiring extra caution
Children and adolescents. The developing brain recovers more slowly and the guidelines set more conservative progressions. When in doubt, always take the more cautious route.
Previous concussions. Each episode increases susceptibility and tends to lengthen recovery from subsequent ones.
A history of migraine, anxiety, depression or learning disorders, which are associated with longer recoveries.
Persistent symptoms. If they're still present at four weeks — two in minors — referral to a specialist service is appropriate. Specific treatments exist: vestibular rehabilitation, vision therapy, prescribed submaximal aerobic exercise.
What doesn't help
Prolonged complete rest. It was the standard advice for years and is now known to worsen outcomes. Gentle, early movement, kept below the symptom threshold.
Routine imaging. A CT scan doesn't diagnose a concussion; it rules out structural injury when red flags are present. Not ordering one doesn't mean there's no concussion.
Returning on how you feel. The criterion is the stepwise progression and medical clearance.
Treating helmets as a free pass. They protect against fractures and cuts; they don't prevent rotational acceleration of the brain. They reduce other injuries; they don't eliminate concussion.
What does help prevent it
The best-supported measures are organizational: limiting contact in training, teaching correct tackling or heading technique, age-adapted rules, neck strengthening in contact sports, and mouthguards, which reduce dental injuries and, according to some studies, perhaps concussions too.
And the most effective of all: a culture where saying "I took a hit and I don't feel right" doesn't cost you your place. Most concussions go unreported for fear of losing playing time.
Final thought
A well-managed concussion usually resolves within one or two weeks with no lasting effects. Badly managed — returning early, hiding symptoms, stacking impacts — it can become a problem lasting months. If you're an athlete, a coach or a parent, the only rule worth memorizing is the one this article opens with: when in doubt, sit it out. No game in the season is worth the risk of a second blow to a brain that's still repairing itself.