The purpose of this randomized controlled trial is to examine whether systematic sub-threshold exercise is effective in improving recovery time in athletes after sport related concussion (SRC) compared to those who participate in a placebo/stretching protocol. subjects will be randomized into either an Exercise group or a Placebo/stretching group. subjects in the Exercise group will participate in an individualized exercise program supervised by their athletic trainer while the Placebo/stretching group will engage in a standardized stretching routine supervised by their athletic trainer throughout the duration of their recovery.

Hypothesis 1: subjects in the aerobic Exercise group will require fewer days to recover from SRC than those who follow a placebo/stretching protocol.

Hypothesis 2: heart rate threshold (HRt) achieved on the graded treadmill test will be associated with days to recovery (i.e., the lower the HRt, the longer the time to recovery).

Hypothesis 3: Vestibular Ocular Motor Screen (VOMS) performance will be indicative of time to clinical recovery from concussion as evidenced by a strong correlation between VOMS score and days to clinical recovery.

Hypothesis 4: Sub-threshold aerobic exercise will facilitate improvement in VOMS post-concussion.

Hypothesis 5: subjects in the aerobic exercise group will demonstrate greater dynamic stability as evidenced by greater reach in each of the 3 primary directions (anterior, posterior medial and posterior lateral) for their right and left lower extremity.

For this randomized controlled trial, a random number generator will be used to randomly assign subjects to either the Placebo/Stretching group or the Exercise group. Study physicians will be blinded to group assignment. Each subject will be given a subject ID number and will complete a brief medical history. They will then be escorted by a designated health care professional who is either the site-coordinator or another health care provider trained in the administration of the Buffalo Concussion Treadmill Test (BCTT) to the treadmill. There, they will be fitted with an ActiGraph activity monitor to be worn throughout their recovery period. The ActiGraph is a small, non-invasive unit that measures human rest and activity cycles. It will be worn similarly to a wrist watch and secured in place with a disposable wristband. Resting heart rate variability (HRV) will be assessed using the Elite HRV app for smartphone. Trained research personnel will assist the subject with fitting the Polar H7 heart rate sensor and finding a comfortable seated position. The heart rate sensor will then connect with the Elite HRV app for smart phone. Once connected, it will take approximately 2 minutes to record the data. Subjects will complete the BCTT in the clinic at the first available testing session no earlier than 48 hours following injury. VOMS and Y-Balance test will also be administered and recorded.

Stretching/Placebo Group Subjects assigned to the Stretching/Placebo group will be given a stretching protocol and instructions to report to their athletic trainer on a daily basis as soon as possible. Prior to the beginning of each intervention session, subjects will be assessed using standard of care protocols which include verbal feedback, symptom scale, and visual-analog scale (VAS). Subjects with a self-reported VAS of ≥7 will not stretch that day. Subjects with a score of ≤ 6 will then complete a 15-25 minute stretching program under supervision by the athletic trainer or other designated research personnel. Following completion of the stretching program for that day, the athletic trainer will record exercise duration and heart rate (HR) (as monitored by the Polar H7 Heart Rate Sensor). The stretching protocol will be progressive and will change weekly as subjects continue their recovery.

Exercise Group Subjects in the exercise group will be prescribed exercise at a target heart rate (THR) of approximately 80% of the achieved heart rate during the BCTT. They will be given this prescription in writing to provide to their athletic trainer. Prior to the beginning of each intervention session, subjects will be assessed using standard of care protocols which include verbal feedback, symptom scale, and visual-analog scale. Subjects with a self-reported Visual Analog Scale (VAS) of ≥ 7 will not exercise that day. Subjects with a score of ≤ 6 will then complete 30 minutes of daily exercise (including 5 minutes of warm up and 5 minutes of cool down) on an exercise bike or walking and supervised by an athletic trainer. Subjects will be instructed to terminate exercise at the first sign of symptom exacerbation or after 30 minutes, whichever occurs first. Athletic trainers will instruct subjects to cease exercise if additional symptoms appear or if symptoms worsen. This program may be modified by increasing heart rate threshold 5-10 beats per minute per week by the athletic trainer as the heart rate for symptom exacerbation increases. The supervising athletic trainer will record exercise duration and THR (as monitored by the Polar H7 Heart Rate Sensor).

Due to medical ethics, subjects will undergo any other individualized rehabilitation recommendations made by the physician or treating physical therapist throughout their individual treatment period. Common rehabilitation interventions include vestibular, oculomotor, cervicogenic, and balance exercises. Subjects may undergo one or all of these depending on their individual needs. Therefore, the exercise protocol identified in this application is a supplement to their standard care provided by medical personnel.

All Subjects All subjects will complete the Symptom Form daily for the duration of their symptom presentation. In addition to reporting to their athletic trainer, subjects will be provided with a link to a secured website on which they will be asked to enter their symptoms at approximately the same time each evening. An option will be to provide the surveys and envelopes to complete these in hard copy.

When symptoms are no longer reported to the athletic trainer by the subject, the athletic trainer will complete the clinical battery associated with their respective concussion protocol prior to the subject's appointment with the study physician to seek clearance for return to play. The study physician will conduct a standardized physical exam and determine if the subject has met the following criteria for clinical recovery:

1. normal or baseline Standardized Assessment of Concussion;
2. normal neurological exam; and
3. can complete the BCTT without symptom exacerbation.
4. VOMS and Y-Balance

Prior to the clearance BCTT, subjects will have Heart Rate Variability (HRV) measured using the Elite HRV app for smart phone. Trained research personnel will assist the subject with fitting the Polar H7 heart rate sensor and finding a comfortable seated position. The heart rate sensor will then connect with the Elite HRV app for smartphone. Once connected, it will take approximately 2 minutes to record the data.

The subject will then begin at Stage 3 of the stepwise return to sport (RTS) strategy as outlined in the Berlin guidelines and full RTS will be allowed when the subject has completed each step of the stepwise RTS criteria without symptom exacerbation. Number of days from date of injury to full RTS (including days in the Berlin RTS) will be recorded, analyzed, and compared for the Placebo/Stretching group and the Exercise group.

Inclusion Criteria:

1. are aged 13-17, years and a high school student-athlete who attends school where an athletic trainer can supervise the exercise protocol;
2. have sustained a concussion within 2-7 days of clinic presentation and diagnosed by a study physician;
3. demonstrate symptom exacerbation during a graded treadmill exercise test and cannot complete the test;
4. are currently participating in a school or club sport;
5. are English speaking and capable of giving assent

Exclusion Criteria:

1. have a reported history of neurological condition or disorder including but not limited to brain surgery, special education, seizure disorder, speech pathology, previous diagnosis of Post-Concussion Syndrome (PCS),
2. are unwilling to exercise,
3. have focal neurologic deficit that would represent risk for walking/running on treadmill,
4. exhibit an inability to exercise due to injury, known heart disease, or increased cardiac risk,
5. have experienced more than 3 previous concussions,
6. have suffered a substantial comorbidity (eg,cervical injury),
7. currently taking β-blockers, calcium channel blockers, or prophylactic headache medications (e.g., amitriptyline, topiramate), or
8. have a resting blood pressure of > 140/90.
9. If the potential participant or parent/guardian is unable to fully understand the study protocol or study risks due to injury or developmental delay, the potential participant will be excluded from the study.

Study physicians will be blinded to group allocation