Traumatic brain injury (TBI) of any severity is associated with decreased heart rate variability, and this autonomic dysfunction can persist long after clinical symptoms resolve. This has major implications for athletes returning to play and anyone recovering from a concussion.
The Evidence
2024 Systematic Review (89 Studies)
A comprehensive 2024 systematic review published in Applied Psychophysiology and Biofeedback examined 89 studies and found [1] accessibility.link.new-tab:
- TBI of any severity is associated with decreased (worse) HRV
- TBI severity moderates the relationship - more severe injuries show greater HRV reduction
- Decreased HRV following TBI predicts mortality beyond age - independent predictor of survival
- HRV disturbances may persist beyond return-to-play and symptom resolution following mild TBI
This is a critical finding: clinical recovery (symptoms gone) does not equal physiological recovery (HRV normalized).
2025 Prognostic Study (172 Patients)
A 2025 study in Neurology and Therapy examined HRV's predictive value in mild-to-moderate TBI [2] accessibility.link.new-tab:
172 patients analyzed (31 unfavorable prognosis, 141 favorable).
Unfavorable prognosis group showed significantly lower:
- SDNN: 75 ms vs 98 ms (p = 0.001)
- RMSSD: 50 ms vs 63 ms (p = 0.019)
- SDNN index: 65 ms vs 86 ms (p < 0.001)
Critical threshold identified: SDNN < 71.5 ms triggers early escalation of care.
Combined prognostic model (GCS + hemoglobin + CK-MB + SDNN index): AUC = 0.939 - one of the strongest predictive values in HRV-prognosis literature.
Concussion Meta-Analysis (6 Studies, 242 Participants)
A 2023 meta-analysis in Frontiers in Neurology specifically examined HRV after concussion [3] accessibility.link.new-tab:
- 109 with concussion history vs 133 controls
- MeanNN significantly different (p = 0.03)
- RMSSD significantly different (p = 0.04)
- Key finding: Lowered HRV persists beyond symptom recovery, reflecting extended autonomic vulnerability
This challenges return-to-play decisions based solely on symptom resolution.
Why TBI Tanks HRV
The autonomic nervous system is particularly vulnerable to brain injury because:
1. Direct brain damage - Autonomic control centers in the brainstem and hypothalamus can be directly injured
2. Diffuse axonal injury - Disrupts connections between brain regions controlling heart rate
3. Inflammation - Neuroinflammation affects autonomic regulation
4. Cerebral blood flow changes - Altered perfusion affects vagal tone
5. Sympathetic hyperactivity - Particularly in severe TBI with paroxysmal sympathetic hyperactivity (PSH)
The Return-to-Play Problem
For athletes, this research raises serious concerns:
- Athletes with concussion displayed autonomic dysfunction that persisted beyond return to play
- The dysfunction was related to previous history of concussion [4] accessibility.link.new-tab
- HRV is suppressed 1-5 days post-concussion, but effects may last weeks
- Physiological recovery appears to outlast clinical recovery
Current return-to-play protocols rely on symptom resolution, but HRV suggests the autonomic system may still be vulnerable even when symptoms are gone.
Intervention Evidence
HRV Biofeedback for TBI
A 2023 systematic review found 7 studies on HRV biofeedback for TBI [5] accessibility.link.new-tab:
- Participants averaged 11 sessions (range: 1-40)
- HRV biofeedback was associated with improved HRV following TBI
- Positive correlations between increased HRV and recovery gains
- Improvements in cognitive and emotional functioning
- Symptom relief from headaches, dizziness, and sleep problems
Important caveat: All 7 studies reported positive results, suggesting possible publication bias. Evidence is "promising but in its infancy."
Aerobic Exercise
A 2024 study on 12-week aerobic exercise for persistent post-concussive symptoms found [6] accessibility.link.new-tab:
- Significant improvement in symptoms, quality of life, headache, dizziness
- However, no significant change in HRV measures after 12 weeks
- May need longer interventions or different approaches for autonomic recovery
Practical Implications
For Athletes:
- Don't rush return-to-play - Symptom resolution doesn't equal autonomic recovery
- Track HRV during recovery - Provides objective physiological data
- Consider HRV-based protocols - Some clinics use HRV normalization as a return criteria
- History of concussion matters - Previous concussions compound autonomic dysfunction
For TBI Survivors:
- Expect autonomic symptoms - Fatigue, exercise intolerance, heart rate irregularities
- HRV monitoring can track recovery - More objective than symptom reports alone
- HRV biofeedback may help - Early evidence is promising
- Be patient - Autonomic recovery can take longer than expected
Clinical Thresholds:
From the 2025 study:
- SDNN < 71.5 ms in mild-to-moderate TBI suggests higher risk
- Combined with clinical factors, HRV achieves AUC = 0.939 for prognosis
The Bottom Line
TBI and concussion significantly reduce HRV across all severity levels. The most concerning finding: autonomic dysfunction persists after clinical symptoms resolve. This matters most for athletes, where return-to-play decisions are currently symptom-based.
If you've had a concussion or TBI:
- Your baseline may be different - Compare to your own recovery trajectory
- Recovery is slower than symptoms suggest - Give yourself time
- Sudden drops during recovery are concerning - May indicate reinjury or overexertion
- Gradual improvement is the goal - Expect weeks to months, not days
Sources
[4] HRV of Athletes Across Concussion Recovery Milestones. PubMed. accessibility.link.new-tab
[5] HRV Biofeedback Treatment Following TBI Systematic Review (2023). PubMed. accessibility.link.new-tab