40% of Healthy Athletes Report Concussion Symptoms at Baseline — Here's Why That Changes Everything

One of the most surprising findings in concussion research: a substantial proportion of healthy, non-concussed athletes report concussion-like symptoms at baseline. A study published in the Journal of Neurotrauma found that up to 40% of healthy athletes endorsed at least one symptom on the Post-Concussion Symptom Scale. Among healthy youth athletes, research by Schneider et al. (2017) published in PMC found that figure climbs even higher — up to 67% report at least one “concussion-like” symptom. The most commonly reported baseline symptoms include fatigue, difficulty concentrating, nervousness, and trouble falling asleep.

Why this matters for clinical decisions

This finding has profound implications for concussion management. If a clinician evaluates a concussed athlete and sees elevated fatigue and difficulty concentrating on their post-injury symptom checklist, they might attribute those symptoms entirely to the concussion. But if the athlete’s baseline shows they reported those same symptoms before any injury, the clinical picture changes completely. Those aren’t new symptoms — they’re that athlete’s normal.

Two kinds of error

Without a personal symptom baseline, clinicians are essentially guessing which symptoms are concussion-related and which are part of the athlete’s everyday experience. This can lead to:

• Over-diagnosis — keeping a healthy athlete out of activity because their normal symptoms look like concussion symptoms.
• Under-diagnosis— attributing genuine new concussion symptoms to the athlete’s “normal” without data to support that assumption.

What inflates baseline symptom reports

The practical lesson is clear: the symptom checklist isn’t just a formality at baseline. It’s clinically essential data. Factors that commonly inflate baseline symptom reports include:

• Poor sleep quality (epidemic among teenagers)
• Academic stress
• Test anxiety during the baseline session itself
• Allergies
• Menstrual cycle-related symptoms

All of these are normal and expected — and all of them can mimic concussion if the clinician doesn’t know they were present before the injury.

How we handle it

At Headquarters, the symptom inventory is a core component of every baseline, administered with the same rigor as cognitive and balance testing. We want to know what your athlete’s “normal” feels like before an injury occurs. That context is invaluable for accurate post-injury care. For the related piece on why symptoms lag behind brain healing, see your symptoms are gone but your brain isn’t healed.

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