Research

Athlete Injury Research: What the Evidence Actually Shows

Summaries of published research on injuries, long-term health and career patterns in professional football and baseball — each with its source, its limits, and what it does and does not mean for a compensation question.

How to read this page

Everything below is drawn from published, citable work — peer-reviewed journals and league-published data. We do not publish our own statistics, and we do not restate study results as predictions about any individual. Population-level research can describe a pattern across thousands of players; whether one player's condition is related to their playing career is a medical and legal question answered by that player's own records.

Each entry lists the study's method and its known limitations, because the limitations are usually the part that gets dropped when these findings are quoted.

Football

Research on Former Football Players

Neurodegenerative death rates were about three times higher than expected

Lehman et al., Neurology (2012) — NIOSH cohort of 3,439 NFL players

Players who spent at least five seasons in the NFL between 1959 and 1988 died of neurodegenerative causes roughly three times more often than men of the same age in the general U.S. population, with the excess concentrated in Alzheimer's disease and ALS. Overall mortality in the same cohort was lower than the general population.

Method & limits

Retrospective cohort study using pension records and national death certificate data. Cause of death came from death certificates, which can misclassify neurodegenerative conditions.

Why it matters for compensation

Findings like this are frequently cited in discussions of whether a neurological condition diagnosed years after retirement may be connected to playing work. A population-level association is not proof about any individual player; causation in a claim is decided on that player's own medical evidence.

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CTE was found in 110 of 111 donated former NFL players' brains

Mez et al., JAMA (2017) — VA-BU-CLF brain bank case series

Neuropathologists diagnosed chronic traumatic encephalopathy in 110 of 111 brains donated by families of former NFL players, and in 177 of 202 brains across all levels of football play.

Method & limits

Convenience case series. Brains were donated largely because families suspected a problem, so the sample is heavily selected and the study cannot show how common CTE is among all former players. CTE also remains a post-mortem diagnosis.

Why it matters for compensation

This study explains why symptom-based neurological claims during life are argued through documented history, imaging and neuropsychological testing rather than a definitive CTE diagnosis.

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Former players report high rates of persistent pain and functional limits

Harvard Football Players Health Study — published findings and study overview

Survey and clinical work with thousands of former NFL players documents widespread ongoing pain, joint problems, sleep disturbance and mobility limitation years after retirement, often across multiple body parts at once.

Method & limits

Ongoing longitudinal research combining self-reported questionnaires with clinical sub-studies. Self-reported outcomes carry recall and participation bias.

Why it matters for compensation

Multi-body-part, gradually worsening complaints are the pattern that cumulative trauma concepts were designed to describe, as opposed to one dated event.

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Injury rates are highest in games and concentrated by position and surface

NFL Injury Data — league-published season injury reports

The league's public reporting tracks concussions and lower-extremity injuries by season, practice versus game exposure and playing surface, and shows game exposure carrying far higher injury rates than practice.

Method & limits

League-collected data reported by club medical staff. Definitions and reporting practices have changed over time, so year-to-year comparisons need care, and pre-2015 seasons are not covered on the same basis.

Why it matters for compensation

Players who retired before modern tracking often have thin contemporaneous records, which is why personal documentation of a career matters more the further back it goes.

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Baseball

Research on Former Baseball Players

Pitchers absorb the majority of injured-list time

Conte et al., studies of MLB disabled/injured list data

Analyses of Major League Baseball disabled-list records consistently find that pitchers account for roughly half or more of all disabled-list assignments and days lost, with shoulder and elbow injuries dominating.

Method & limits

Retrospective review of league transaction and disabled-list records. Roster moves are an imperfect proxy for injury severity.

Why it matters for compensation

Repetitive throwing injuries usually accumulate over many seasons rather than beginning on one date — the fact pattern that cumulative trauma analysis addresses.

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Ulnar collateral ligament reconstruction has risen sharply

Erickson et al., American Journal of Sports Medicine — UCL reconstruction trends

The rate of UCL reconstruction (Tommy John surgery) among professional pitchers increased substantially over the studied period, and a meaningful share of pitchers did not return to their prior level of performance.

Method & limits

Review of publicly reported surgeries and performance data. Public reporting can undercount minor-league procedures.

Why it matters for compensation

Return-to-play statistics are about performance, not about whether a residual impairment exists later in life. Those are separate questions.

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Careers are short, and most professional service is in the minors

Witnauer, Rogers & Saint Onge, Demography (2007) — MLB career length analysis

Analysis of position-player careers found a median major-league career of roughly five years, with a large share of players lasting far less. Most professional baseball service time is spent in the minor leagues.

Method & limits

Life-table analysis of historical player records for position players; the estimate does not describe pitchers or modern seasons exactly.

Why it matters for compensation

Where a player was employed, by which club entity, and in which states matters for eligibility — minor-league seasons are still employment even when they are the part players remember least clearly.

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What the research does not settle

How common long-term neurological disease is among all former players — the brain-bank studies use selected samples, not representative ones.
Whether any individual's arthritis, back condition or cognitive symptoms came from playing rather than from other causes.
How a specific state's law treats a condition that developed across many seasons and several employers.
What any particular claim may be worth — research describes health patterns, not benefit amounts.

For how those questions are approached in practice, start with the complete guide to professional athlete injury compensation or the explanation of cumulative trauma.