Two things can be true at once. Sport is, on balance, very good for you. And repeated head impact — even when no single one looks dramatic — appears to carry long-term risk that the field is still working out the shape of. This article is a brief tour of what’s currently understood and what’s still being argued about.
What concussion actually is
Concussion is a clinically diagnosed event: a transient disturbance of brain function after a head impact, defined by symptoms (headache, confusion, balance loss, slowed processing, sometimes amnesia) and confirmed by examination rather than by any imaging finding. Most concussions resolve within days to weeks. A minority leave longer trails of symptoms, particularly when someone returns to play before recovery is complete.
A concussion is not the same as a structural brain injury. CT and MRI scans of newly concussed athletes typically come back normal. The injury is functional — to the way neurons signal — rather than to the gross anatomy of the brain.
Sub-concussive impacts
The more recent and less well-understood category is the sub-concussive impact: a head loading event that produces no symptoms, no clinical signs, and no immediate change in performance. A tackle, a header, a body-check. Individually, they look like nothing. Cumulatively, in some athletes, in some sports, they appear to do real harm.
The research case is built from a few converging strands:
- Imaging. Diffusion-tensor MRI studies of athletes across seasons show changes in white-matter integrity that correlate with cumulative head-impact exposure rather than with diagnosed concussions.
- Post-mortem pathology. Studies of donated brains from former contact-sport athletes find tau protein deposits in patterns distinct from typical age-related changes.
- Cohort epidemiology. Long-term follow-up studies of former rugby, football, and ice-hockey players show elevated rates of neurodegenerative disease compared with matched populations.
What CTE is and isn’t
Chronic Traumatic Encephalopathy (CTE) is the neuropathological diagnosis given when a brain — examined after death — shows a specific pattern of tau-protein deposition around small blood vessels in the brain’s folds. It can currently only be diagnosed post-mortem. Symptoms reported in life that correlate with CTE pathology include behavioural change, memory disruption, and mood disturbance, often beginning years after a sporting career ends.
The honest scientific picture, as of writing:
- CTE-pattern pathology is disproportionately common in former contact-sport athletes.
- Not every athlete with high career impact exposure develops it; not every case of behavioural change in an ex-athlete is CTE.
- The dose-response between specific impact metrics and risk is still being mapped. This is exactly the gap where trace* and tools like it are aimed.
Why measuring exposure matters
If you cannot diagnose CTE in life, and you cannot perfectly predict which exposures will lead to harm in which athletes, then the single most useful thing you can do is measure exposure carefully and longitudinally. That gives:
- Athletes the information to make their own career decisions.
- Coaches the information to manage practice load.
- Researchers the data to refine the dose-response models that will eventually inform policy.
- Governing bodies the evidence to design rule changes that target the impacts that matter.
trace* is one of many tools pointed at that goal. Its contribution is the speed and accessibility piece — making per-region strain estimates routinely available, rather than reserving them for the small number of impacts that ever reach a research lab.
Sources & further reading
- McKee, A. C. et al. (2009) — Chronic Traumatic Encephalopathy in athletes. J. Neuropathol. Exp. Neurol. 68 (7).
- Sharp, D. J. & Jenkins, P. (2015) — Concussion is confusing us all. Practical Neurology 15 (3).
- Bailes, J. E. et al. (2013) — Role of subconcussive impact in sport-related concussion. J. Neurosurgery 119 (5).
- Mainwaring, L. et al. (2018) — Subconcussive head impacts in sport: a systematic review of the evidence. — Converging imaging, cognitive and physiological findings across contact sports.