Symptoms Associated With Exercise Intolerance and Resting Heart Rate Following Mild Traumatic Brain Injury

Objectives:People may experience a myriad of symptoms after mild traumatic brain injury (mTBI), but the relationship between symptoms and objective assessments is poorly characterized. This study sought to investigate the association between symptoms, resting heart rate (HR), and exercise tolerance in individuals following mTBI, with a secondary aim to examine the relationship between symptom-based clinical profiles and recovery. Methods:Prospective observational study of adults aged 18 to 65 years who had sustained mTBI within the previous 7 days. Symptoms were assessed using the Post-Concussion Symptom Scale, HR was measured at rest, and exercise tolerance was assessed using the Buffalo Concussion Bike Test. Symptom burden and symptom-based clinical profiles were examined with respect to exercise tolerance and resting HR. Results:Data from 32 participants were assessed (mean age 36.5 +/- 12.6 years, 41% female, 5.7 +/- 1.1 days since injury). Symptom burden (number of symptoms and symptom severity) was significantly associated with exercise intolerance (P = .002 and P = .025, respectively). Physiological and vestibular-ocular clinical profile composite groups were associated with exercise tolerance (P = .001 and P = .014, respectively), with individuals who were exercise intolerant having a higher mean number of symptoms in each profile than those who were exercise tolerant. Mood-related and autonomic clinical profiles were associated with a higher resting HR (>80 bpm) (P = .048 and P = .028, respectively), suggesting altered autonomic response for participants with symptoms relating to this profile. After adjusting for age and mechanism of injury (sports- or non-sports-related), having a higher mood-related clinical profile was associated with persisting symptoms at 3 months postinjury (adjusted odds ratio = 2.08; 95% CI, 1.11-3.90; P = .013). Conclusion:Symptom-based clinical profiles, in conjunction with objective measures such as resting HR and exercise tolerance, are important components of clinical care for those having sustained mTBI. These results provide preliminary support for the concept that specific symptoms are indicative of autonomic dysfunction following mTBI.