BACKGROUND: Aerobic exercise has emerged as a useful treatment to improve outcomes among individuals who experience a concussion. However, compliance with exercise recommendations and the effect of exercise volume on symptom recovery require further investigation. PURPOSE: To examine (1) if an 8-week aerobic exercise prescription, provided within 2 weeks of concussion, affects symptom severity or exercise volume; (2) whether prescription adherence, rather than randomized group assignment, reflects the actual effect of aerobic exercise in postconcussion recovery; and (3) the optimal volume of exercise associated with symptom resolution after 1 month of study. STUDY DESIGN: Cohort study; level of evidence, 2. METHODS: Individuals randomized to an exercise intervention (n = 17; mean age, 17.2 +/- 2.0 years; 41% female; initially tested a mean of 11.3 +/- 2.8 days after injury) or standard of care (n = 20; mean age, 16.8 +/- 2.2 years; 50% female; initially tested a mean of 10.7 +/- 3.2 days after injury) completed an aerobic exercise test within 14 days of injury. They returned for assessments 1 month and 2 months after the initial visit. The aerobic exercise group was instructed to exercise 5 d/wk, 20 min/d (100 min/wk), at a target heart rate based on an exercise test at the initial visit. Participants reported their exercise volume each week over the 8-week study period and reported symptoms at each study visit (initial, 1 month, 2 months). Because of low compliance in both groups, there was no difference in the volume of exercise between the 2 groups. RESULTS: There were no significant symptom severity differences between the intervention and standard-of-care groups at the initial (median Post-Concussion Symptom Inventory, 15 (interquartile range 10 to 42) versus 20 (11 to 35.5); p = 0.26), 1-month (4 (0 to 28) versus 5.5 (0.5 to 21.5); p = 0.96), or 2-month (6.5 (0 to 27.5) versus 0 (0, 4); p = 0.11) study visits. Exercise volume was similar between groups (median, 115 (54, 225) versus 88 (28, 230) min/wk for exercise intervention versus standard of care; p = 0.52). Regardless of group, those who exercised < 100 min/wk reported significantly higher symptom severity at the 1-month evaluation compared with those who exercised >= 100 min/wk (median, 1.5 (0 to 7.5) versus 12 (4 to 28); p = 0.03). Exercising >= 160 min/wk successfully discriminated between those with and those without symptoms 1 month after study commencement (classification accuracy, 81%; sensitivity, 90%; specificity, 78%). CONCLUSION: Greater exercise volume was associated with lower symptom burden after 1 month of study, and an exercise volume > 160 min/wk in the first month of the study was the threshold associated with symptom resolution after the first month of the study. Because our observation on the association between exercise volume and symptom level is a retrospective and secondary outcome, it is possible that participants who were feeling better were more likely to exercise more, rather than the exercise itself driving the reduction in symptom severity.

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