This Randomized Controlled Trial (RCT) will explore the effect of sub-symptom threshold aerobic exercise on persistent post-concussion symptoms and exercise intolerance in patients with mild Traumatic Brain Injury (TBI). The hypothesis is that sub-symptom training will reduce the symptom pressure, normalize exercise tolerance, reduce patient-specific activity limitations and improve health-related quality of life. To improve the chances of conducting a high-quality RCT, a feasibility trial will be completed prior to the definitive RCT.

Background: Persistent post-commotio symptoms (PCS) affect between 34% and 46% of individuals after a mild traumatic brain injury (TBI). Many also experience exercise intolerance. Sub-symptom threshold aerobic exercise (exercise at an intensity level that does not increase symptoms) is proposed as treatment both to increase the exercise tolerance and to ease the symptom burden after the injury.

Main purpose: The main purpose of this study is to evaluate whether a progressive sub-symptom threshold exercise program in addition to ordinary rehabilitation will lead to clinically meaningful improvement of symptom burden, normalize exercise tolerance, increase physical activity, improve health-related quality of life, and reduce patient-specific activity limitations compared to a control group that only receives ordinary rehabilitation.

Design: Randomized, controlled, single-blind parallel-group study with three measurement times; T0 at baseline, T1 after the intervention and T2 six months after T1.

Method: 68 patients between the ages of 18 and 60 with exercise intolerance and persistent PCS will be recruited to the study and randomized to two groups. All participants will receive ordinary rehabilitation. The intervention group will in addition receive sub-symptom threshold aerobic exercise for 12 weeks with weekly follow-up by a physiotherapist and a retest every 3 weeks for optimal dosage and progression. Rivermead post-concussion symptoms questionnaire (RPQ) will be the main outcome measure. The secondary outcome measure will be a test of exercise tolerance - the Buffalo Concussion Treadmill Test (BCTT). Other outcome measures include the patient-specific functional scale that measures patient-specific activity limitations, as well as outcome measures for health-related quality of life, anxiety and depression, specific symptoms such as dizziness, headache and fatigue, and level of physical activity.

Clinical relevance: Since people with persistent symptoms after mild TBI often have reduced level of functioning and difficulty working / studying full time, there is a great need for an individually tailored intervention that has the potential to reduce persistent symptoms and improve functioning This project will increase the evidence based knowledge about the effect of sub-symptom threshold aerobic exercise in patient with persistent symptoms after mild TBI.

Inclusion Criteria:

• Patients with mild TBI defined by the World Health Organization (WHO) Collaborating Center Task Force definition: 1) one or more of the following: confusion or disorientation, loss of consciousness (LOC) ≤30 minutes, post-traumatic memory loss (PTA) ≤24 hours and / or transient neurological focal deficits and intracranial lesions that do not require surgery; 2) Glasgow Coma Scale (GCS) score of 13-15 at least 30 minutes after trauma).
• 18-60 years with persistent post-commotio symptoms (minimum 3 months maximum 2 years).
• Reduced tolerance to physical activity/exercise intolerance (self-reported worsening of symptoms such as dizziness and headache during physical activity and exercise).

Exclusion Criteria:

• Other neurological or psychiatric conditions (not including anxiety and depression) listed in the medical record. Heart-lung disease, extremity injuries that prevent physical exercise, drug addiction and insufficient understanding of the Norwegian language (unable to follow instructions and/or fill in forms). Normal BCTT.

After written informed consent, patients will be randomized to the intervention or control group using computer-generated lists. Block randomization with variable block size that is unknown to the research group will be used. Follow-up tests at T1 and T2 will be performed by a research assistant who is blind to the group distribution and who is not involved in any parts of the intervention. Statisticians will be blinded to group allocation.