- Symptom status and neurocognitive performance were affected by postconcussive activity levels and age and sex of the athlete.
- Younger adolescents experienced more pronounced deficits in verbal and visual memory than older teenagers after concussion.
- Moderate levels of exertion were associated with better symptom and neurocognitive performance prognosis, suggesting controlled exertion may improve outcome after concussion. More study in this area is needed.
More than 1
000 mild traumatic brain injuries (TBIs) occur each year in the United States.1
The average incidence of mild TBI from all causes in the United States is estimated at 503 per 100
000, with bicycles and sports accounting for 26.4% in the 5-year-old to 14-year-old age group.1
Conservative estimates indicate that more than 300
000 sport-related concussions occur each year in the United States2
: more than 60
000 cases of concussions occur at the high school level, with football accounting for the majority of these.3
Approximately 4% of high school and collegiate football players sustain concussions during each season.3–,5
With more than 1
000 student-athletes participating at the high school level,6
this is an especially important population to examine. A discussion of sex differences in clinical measures of concussion has recently been published,7
showing that males tended to perform better on visual memory, while females performed better on verbal memory tasks; females also typically endorsed a higher number of symptoms during preseason baseline screening. Epidemiologic studies on collegiate football players have also demonstrated that concussed players' symptoms typically resolved within 7 days and neurocognitive function returned to baseline levels within 5 to 7 days.8
Not much is known about the age-related differences in postconcussive symptoms, and whether symptoms of concussion can significantly interfere with the cognitive activities student-athletes require for schoolwork is an area yet to be explored.
Concussion is a mild TBI that results from a biomechanical insult to the brain that initiates a destructive neurometabolic cascade of events.9
The cascade begins with the release of excitatory neurotransmitters, which result in cellular membrane disruption and ionic imbalances. Increasing amounts of adenosine triphosphate (ATP) are required in an attempt to correct these ionic imbalances, and an increase in glucose metabolism is observed within the first 24 hours after concussion. This increased glucose metabolism, combined with an initial decrease in cerebral blood flow, results in a mismatch between the energy required and that available to brain structures. The increase in glucose metabolism is followed by a period of reduced glucose uptake and metabolism, which may last for as long as 1 month.9
Exercise also modulates glucose uptake in the brain and increases cortisol in a dose-dependent manner, both of which could worsen the neuronal energy mismatch after concussion.10,11
Most of these studies have been performed on animal models. Although the generalizability to humans is limited, these models display many pathophysiologic and behavioral characteristics noted in the human condition. As such, they may provide us with some insight for clinical phenomena observed in human brain injuries. Further worsening of traumatically induced metabolic mismatch may occur with exercise or other types of activity. Worsening of postconcussive memory deficits and processing speed after cognitively demanding tasks has also been demonstrated.12
In addition, variations in postconcussive symptoms with respect to subjective levels of stress have been reported.13
Given the proposed metabolic abnormalities associated with concussion, which may last longer than once believed, the decision on when and how to return an athlete to play has received attention as a national public health issue.14
Postconcussive activity has been clinically noted to worsen symptoms and cognition after concussion. Most of the existing guidelines have been specifically developed for return to play rather than return to the functional activities of school, work, or daily chores. Therefore, we aimed to examine the role of postinjury activity level in post-concussive symptoms and performance on neurocognitive tests in a population of student-athletes. Our hypothesis was that athletes who engaged in high levels of activity after a concussion would have higher symptom severity scores and slower recoveries than those who engaged in lower activity levels during recovery.