How the Standard of Care for Concussion Moved from Passive to Active Treatment
The first International Consensus Conference on Concussion in Sport was held in Vienna in 2001. It produced a return play guideline that called for the athlete to progress through various stages based on level of exertion and gradual introduction to game-like conditions. It advised that an athlete should not begin the return to play process until asymptomatic. Finally, it recommended a management strategy based on complete rest (some even called it extreme rest, or “cocooning” in a dark room with no access to devices).
Also in 2001, there were important new findings from research on rats, led by Dr. Christopher Giza at UCLA. This research identified the metabolic changes that accompany concussion. One observation was a reduced level of cerebral blood flow (CBF). This animal research also found that when rats were forced to exercise after simulated concussion they had slower recovery, thus supporting the ‘rest is best’ model.
The original Vienna guidelines implied that if athletes can exercise to the level of their sport without exacerbation of symptoms, they were safe to return to play. Another way to view this is that individuals with concussion are exercise intolerant. Our research began with a goal to develop a more systematic way to assess exercise (in)tolerance. Rather than have an athlete run on a field or skate on the ice, we developed the Buffalo Concussion Treadmill Test. Our research on the physiology of concussion required a reliable and valid approach to assessment. We found it fascinating how overtly patients demonstrated symptom exacerbation during exercise testing.
Our original goal in research was to explain the physiology behind exercise intolerance. A number of important findings produced a more coherent pattern of concussion pathophysiology, which appeared to be related to the autonomic nervous system (ANS). The ANS has two arms: the sympathetic (‘flight or fight’) and the parasympathetic (‘rest and digest’). At rest, the concussed athletes had higher than normal heart rates (HR) as well as reduced CBF (just like the rats). All of this implied that concussed athletes were in a sympathetic state at rest. The subjective experience of the athlete would be to feel ‘anxious’ and in a sympathetic state our pupils are wider, which explains the common symptom of light sensitivity.
When someone is experiencing increasing physical demands during aerobic exercise, the ANS should become more sympathetic to meet the metabolic demand. The concussed athlete with increased sympathetic activity at rest, interestingly, does not exhibit the normal response. We have shown that their HR does not rise to match the level of exercise intensity and so they find exercise more fatiguing than they should. Further, when someone should become parasympathetic (e.g., after meals and when getting ready to fall asleep), concussed individuals do not achieve a parasympathetic state, either. Sleep difficulties and nausea are common symptoms of concussion, so inability to achieve the appropriate state within the ANS is associated with recognized post-concussion symptoms.
Our research in combination with research from other labs was beginning to explain the physiology of concussion, and it was exciting that we were able to identify measurable alterations of the ANS that were consistent with the subjective experience of patients. We were also very excited to finally explain why someone with concussion has exercise intolerance. During exercise, CBF should remain stable, but for those with a concussion there is a sudden increase in CBF during exercise that produces symptom exacerbation. For someone just days after concussion, this sudden increase in CBF will usually occur at a very low heart rate (HR) and stop exercise. This HR threshold is a very important indicator of the severity of the concussion.
Having established that concussion produces significant alterations in the ANS and CBF, the next question became: Can we use this information to develop better treatment? The logical treatment for restoring control of the ANS and CBF is regular aerobic exercise. The safest way to do this was to prescribe exercise at a HR that was below the HR threshold at which patients experienced symptom exacerbation.
The research on concussion physiology has provided much of the information that was needed to explain why sub-threshold exercise should speed recovery, but it took a major study to prove that it works. We just completed that study and it was published last month in JAMA Pediatrics. This was a randomized clinical trial where 103 adolescent athletes with acute concussion (within days of their injury) were randomly assigned to sub-threshold exercise or a placebo-like control condition (stretching exercises). The treating doctors were blinded to the group assignment. Patients in the aerobic exercise group recovered faster and fewer patients in the aerobic exercise group had delayed recovery. This latter finding was a pleasant surprise. Patients with delayed recovery have a horrible experience with their concussion and they are a huge cost to the health care system.
We chose to study adolescents because they have the highest rate of concussive injury and take longer than adults or children to recover. It is reasonable to ask, will aerobic exercise also work for children and adults, and what about non-athletes? We believe exercise will help everyone with a concussion. Our thoughts are that non-athletes may not recover as quickly as athletes but should recover faster with prescribed exercise than with rest. Rest in fact is counterproductive to regaining control over the ANS and so should not be the treatment of choice. As it turns out, recent research has shown that rats recover faster when allowed to exercise at their own pace yet have poorer recovery when forced to rest.
In 2016 the International Consensus Conference in Berlin revised the prior position on activity after concussion. The guidelines now state that management should include relative rest for the first 48 hours followed by a gradual and progressive return to activity, while staying below the individual’s symptom-exacerbation threshold. We are delighted to have played a role in creating proactive treatment for concussion, but there is much more to accomplish to make diagnosis and management of concussion truly effective.