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Bias-Adjusted Prevalence of Chronic Traumatic Encephalopathy Among Deceased National Football League Players

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Abstract

ImportanceThe majority of knowledge regarding chronic traumatic encephalopathy (CTE) in National Football League (NFL) players is derived from autopsy-based studies on voluntarily donated brains. Because these cohorts are highly vulnerable to selection bias (specifically registry bias), population-level prevalence of CTE among former NFL players is unknown, limiting understanding of the impact of this disease.ObjectiveTo estimate the selection-bias adjusted prevalence of CTE neuropathology in deceased NFL players.

Design, Setting, and Participants

This population-based cross-sectional study used Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) brain bank data combined with National Death Index records on former NFL players. Both brain donor and nondonor NFL players who died between January 2008 and December 2023 were included. Data were analyzed from November 2025 to April 2026.

Exposure

Playing in at least 1 regular or postseason NFL game.

Main Outcomes and Measures

The main outcomes of this study were bias-adjusted prevalence of CTE neuropathology and all-cause dementia among the target population, both of which were measured in donors prior to this study. A cognitive symptom–related brain donation selection ratio (probability of donation given CTE divided by the probability of donation given no CTE) was estimated using Poisson regression and was applied to adjust donor-observed prevalence of CTE neuropathology at death and all-cause dementia during life. The prevalence estimates were adjusted for bias using the estimated selection ratio.

Results

The cohort consisted of 2362 deceased former NFL players (mean [SD] years played, 5.1 [3.9]; 971 [41.1%] aged ≥80 years at death), of whom 396 were brain donors and 1966 were nondonors. Of 387 donors, 362 (93.5%) had CTE. The median selection ratio was 4.97 (95% CI, 4.72-5.26). Bias-adjusted population prevalence of CTE at death was 74.5% (95% CI, 69.6%-78.3%), with a conservative lower-bound analysis estimating 63.7% (57.2%-68.9%). Bias-adjusted population prevalence of all-cause dementia history during life was 27.2% (95% CI, 22.6%-31.6%).

Conclusions and Relevance

The findings of this cross-sectional study suggest that selection bias materially inflates donor-based prevalence estimates but is unlikely to fully explain the high burden of CTE neuropathology among this population. Further research is required to understand the clinical impact of this disease.

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Transcranial Photobiomodulation Promotes Neurological Resilience in Current Collegiate American Football Players Exposed to Repetitive Head Acceleration Events

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Abstract

Repetitive head acceleration events (RHAE) are common in contact sports and associated with neuroinflammation, axonal injury, and long-term neurological impairments, including increased risk for chronic traumatic encephalopathy. Current strategies for addressing RHAE focus on post-injury care rather than proactive neuroprotection, leaving athletes vulnerable to cumulative neurotrauma. Transcranial photobiomodulation (PBM) has shown promise in reducing neuroinflammation and promoting neuroprotection in traumatic brain injury; however, its potential to mitigate the structural brain changes associated with RHAE in actively competing athletes has not been investigated. The aim of this study was to investigate whether PBM mitigates RHAE-related neuroinflammatory and microstructural changes in collegiate American football players over a single National Collegiate Athletic Association Division I season.

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Effects of repeated head trauma in young athletes

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Abstract

People can be exposed to repetitive impacts to the head in contact sports, military service, falls, and other situations. Repeated head trauma raises the risk of developing chronic traumatic encephalopathy (CTE), a progressive degenerative disease that can bring problems with thinking, understanding, and communicating. It may also cause movement disorders, problems with impulse control, depression, mood swings, confusion, and irritability.

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The Effect of Photobiomodulation Therapy on Muscle Performance in Volleyball and Football Players: A Meta-Analysis of Randomized Controlled Trials

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Abstract

The use of photobiomodulation therapy (PBMT) as an adjunct to improve muscle performance and accelerate recovery in high-level volleyball and football players remains controversial.

Objective:

To determine whether PBMT improves skeletal muscle performance in ball sports athletes, and whether there are differences in the improvement of skeletal muscle performance by PBMT between volleyballers and footballers.

Data Sources:

A comprehensive search of the Web of Science, Medline, Scopus, and PubMed databases was conducted through April 10, 2025.

Study Selection:

Eligible studies included those explicitly categorized as randomized controlled trials (RCT) of PBMT interventions for high-level volleyballers and/or footballers; 14 studies met the inclusion criteria.

Study Design:

Meta-analysis.

Level of Evidence:

Level 2.

Data Extraction:

The primary outcome measures included maximal voluntary contraction force (MVC), number of repetitions, and creatine kinase (CK) levels. Means and standard deviations for each variable of interest were used to calculate standardized mean differences (SMDs).

Results:

The active laser had no significant effect on MVC (mean difference [MD], 19.67; 95% CI, 7.36 to 31.72; P = 0.31)]; however, it significantly increased the number of repetitions (SMD, 0.58; 95% CI, –0.05 to 1.21; P = 0.04) and significantly decreased CK levels (MD, –45.37; 95% CI, –55.52 to −35.22; P < 0.001).

Conclusion:

PBMT can delay muscle fatigue onset and reduce CK levels in ball sports athletes. The improvement in skeletal muscle performance induced by PBMT showed differences between volleyballers and footballers, as there was a significant increase the number of repetitions in volleyball players, whereas a significant decrease in CK levels was noted in footballers.

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Photobiomodulation as Medicine: Low-Level Laser Therapy (LLLT) for Acute Tissue Injury or Sport Performance Recovery

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Abstract

Background/Objectives:

Low-level laser therapy (LLLT) has gained traction in sports and exercise medicine as a non-invasive therapeutic for preconditioning the body, exertion recovery, repair and injury rehabilitation. LLLT is hypothesized to modulate cellular metabolism, tissue microenvironment(s) and to decrease inflammation while posing few adverse risks. This review critically examines the evidence-base for LLLT effectiveness focusing on immediate care settings and acute/subacute applications (<6 months post-injury).

Methods: A comprehensive literature search was conducted, prioritizing systematic reviews, meta-analyses and their primary research papers.

Results: Findings are relevant to trainers and athletes as they manage a wide range of issues from superficial abrasions to deeper tissue concerns. LLLT parameters in the research literature include wide ranges. For body surface structures, studies show that LLLT holds promise in accelerating wound healing. In sport performance studies, LLLT is typically delivered pre-exercise and reveals beneficial effects on exertion recovery, improvements in muscle strength, endurance and reduced fatigue. Evidence is less convincing for acute, deep tissue injury models, where most studies do not report significant benefits for functional outcomes over conventional therapeutic modalities.

Conclusions: Variability in LLLT delivery parameters and findings across studies underscores a need for clear treatment guidelines for the profession. Technical properties of laser light delivery to the body also differ materially from LED devices. Sport physiotherapists, team physicians, trainers and athletes should understand limitations in the current evidence-base informing photobiomodulation use in high-performance sport settings and weigh potential benefits versus shortcomings of LLLT use in the mentioned therapeutic contexts.

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The Effect of Intranasal Plus Transcranial Photobiomodulation on Neuromuscular Control in Individuals with Repetitive Head Acceleration Events

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Introduction
Approximately 3.8 million sport- and recreation-related concussions occur annually in the United States. The effects of concussion, including persistent long-term issues with concentration and physical skills is a growing concern. Equally concerning are the effects of repetitive head impacts (RHIs), also known as repetitive head acceleration events (RHAEs). RHAE has the same meaning as RHI; however, it is emerging as a preferred term because it inherently indicates that the brain is experiencing translational and/or rotational movement because of external forces regardless of the source (blast or mechanical blow) or location (head or body) of the impact forces. Although RHAE may include concussions or mild traumatic brain injury (mTBI), most do not result in any acute detectable clinical symptoms. However, the cumulative effect of RHAE, like concussion or mTBI, could progress to traumatic encephalopathy syndrome (TES), a clinical disorder associated with chronic traumatic encephalopathy (CTE). An athlete may experience over 100 RHAEs per season. Although the athlete may be asymptomatic, RHAEs result in microstructural and functional changes in the brain similar to that seen in concussion or mTBI, leading to altered motor unit recruitment strategies, increased acute corticomotor inhibition, and other neuromuscular impairments, such as reduced dynamic balance or reaction time, in the long-term.

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The Differences between Blast-Induced and Sports-Related Brain Injuries

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Abstract

Both blast-induced traumatic brain injury (TBI) and sports-related concussion are occasionally considered to have similar injury mechanisms by which repeated head impacts cause chronic traumatic encephalopathy (CTE). Patients with the two conditions experience comparable CTE symptoms, such as headache, light-headedness, memory loss, confusion, attention deficits, difficulty balancing, aggression, anxiety, depression, etc. (1). Another common feature is tau protein deposition around cerebral blood vessels in the frontal cortex (2, 3). However, it should be noted that these symptoms are non-specific, and can be the results of many different brain insults such as TBI, stroke, chemically induced neurotoxicity, infection by pathogenic microbes (HIV virus, bacteria, etc.), brain tumors, and neurodegenerative diseases (Parkinson’s, Alzheimer’s, ALS, Huntingtons, etc.). Abnormal or hyper-phosphorylated tau protein deposition is also non-specific and represents only disruption and dysfunction of microtubules in neuronal cells that are experiencing progressive death and degeneration. Therefore, having similar mental symptoms and tau protein deposition in the same regions of the brain does not conclude that the same basic injury mechanism existed in both blast-induced and sports-related brain injuries.

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