relative physical and cognitive rest. this can include gentle daily activities such as walking in the house, gentle housework, and light school work that do not make symptoms worse. no sports activities. stage 2: light aerobic activity such as walking or stationary cycling stage 3: sport-specific activities such as running drills and skating drills stage 4: non-contact training drills (exercise, coordination, and cognitive load) stage 5: full-contact practice (requires medical clearance) stage 6: return to full-contact sport or high-risk activities (requires medical clearance) at each step, the person should not have worsening or new symptoms for at least 24 hours before progressing to the next. if symptoms worsen or new symptoms begin, athletes should drop back to the previous level for at least another 24 hours. intercollegiate or professional athletes, are typically followed closely by team athletic trainers during this period but others may not have access to this level of health care and may be sent home with minimal monitoring. medications medications may be prescribed to treat headaches, sleep problems and depression. analgesics such as ibuprofen can be taken for headaches, but paracetamol (acetaminophen) is preferred to minimize the risk of intracranial hemorrhage. concussed individuals are advised not to use alcohol or other drugs that have not been approved by a doctor as they can impede healing. activation database-guided eeg biofeedback has been shown to return the memory abilities of the concussed individual to levels better than the control group. about one percent of people who receive treatment for mtbi need surgery for a brain injury. return to work determining the ideal time for a person to return to work will depend on personal factors and job-related factors including the intensity of the job and the risk of falling or hitting one's head at work during recovery. after the required initial recovery period of complete rest (24–48 hours after the concussion began), gradually and safely returning to the workplace with accommodations and support in place, should be prioritized over staying home and resting for long periods of time, to promote physical recovery and reduce the risk of people becoming socially isolated. the person should work with their employer to design a step-wise "return-to-work" plan. for those with a high-risk job, medical clearance may be required before resuming an activity that could lead to another head injury. students should have completed the full return-to-school progression with no academic accommodations related to the concussion required before starting to return to part-time work. prognosis the majority of children and adults fully recover from a concussion, however some may experience a prolonged recovery. there is no single physical test, blood test (or fluid biomarkers), or imaging test that can be used to determine when a person has fully recovered from concussion. a person's recovery may be influenced by a variety of factors that include age at the time of injury, intellectual abilities, family environment, social support system, occupational status, coping strategies, and financial circumstances. factors such as a previous head injury or a coexisting medical condition have been found to predict longer-lasting post-concussion symptoms. other factors that may lengthen recovery time after mtbi include psychological problems such as substance abuse or clinical depression, poor health before the injury or additional injuries sustained during it, and life stress. longer periods of amnesia or loss of consciousness immediately after the injury may indicate longer recovery times from residual symptoms. other strong factors include participation in a contact sport and body mass size. pediatric concussion most children recover completely from concussion in less than four weeks, however 15–30% of youth may experience symptoms that last longer than a month. people aged 65+ with concussion mild traumatic brain injury recovery time in people over age 65 may have increased complications due to elevated health concerns, or comorbidities. this often results in longer hospitalization duration, poorer cognitive outcomes, and higher mortality rates. repeat concussion for unknown reasons, having had one concussion significantly increases a person's risk of having another. having previously sustained a sports concussion has been found to be a strong factor increasing the likelihood of a concussion in the future. people who have had a concussion seem more susceptible to another one, particularly if the new injury occurs before symptoms from the previous concussion have completely gone away. it is also a negative process if smaller impacts cause the same symptom severity. repeated concussions may increase a person's risk in later life for dementia, parkinson's disease, and depression. post-concussion syndrome main article: post-concussion syndrome in post-concussion syndrome, symptoms do not resolve for weeks, months, or years after a concussion, and may occasionally be permanent. about 10% to 20% of people have post-concussion syndrome for more than a month. symptoms may include headaches, dizziness, fatigue, anxiety, memory and attention problems, sleep problems, and irritability. rest, a previously recommended recovery technique, has limited effectiveness. a recommended treatment in both children and adults with symptoms beyond 4 weeks involves an active rehabilitation program with reintroduction of non-contact aerobic activity. progressive physical exercise has been shown to reduce long-term post-concussive symptoms. symptoms usually go away on their own within months but may last for years. the question of whether the syndrome is due to structural damage or other factors such as psychological ones, or a combination of these, has long been the subject of debate. cumulative effects as of 1999, cumulative effects of concussions were poorly understood, especially the effects on children. the severity of concussions and their symptoms may worsen with successive injuries, even if a subsequent injury occurs months or years after an initial one. symptoms may be more severe and changes in neurophysiology can occur with the third and subsequent concussions. as of 2006, studies had conflicting findings on whether athletes have longer recovery times after repeat concussions and whether cumulative effects such as impairment in cognition and memory occur. cumulative effects may include chronic traumatic encephalopathy, psychiatric disorders and loss of long-term memory. for example, the risk of developing clinical depression has been found to be significantly greater for retired american football players with a history of three or more concussions than for those with no concussion history. an experience of three or more concussions is associated with a fivefold greater chance of developing alzheimer's disease earlier and a threefold greater chance of developing memory deficits. chronic traumatic encephalopathy, or "cte", is an example of the cumulative damage that can occur as the result of multiple concussions or less severe blows to the head. the condition was previously referred to as "dementia pugilistica", or "punch drunk" syndrome, as it was first noted in boxers. the disease can lead to cognitive and physical disabilities such as parkinsonism, speech and memory problems, slowed mental processing, tremor, depression, and inappropriate behavior. it shares features with alzheimer's disease. second-impact syndrome main article: second-impact syndrome second-impact syndrome, in which the brain swells dangerously after a minor blow, may occur in very rare cases. the condition may develop in people who receive a second blow days or weeks after an initial concussion before its symptoms have gone away. no one is certain of the cause of this often fatal complication, but it is commonly thought that the swelling occurs because the brain's arterioles lose the ability to regulate their diameter, causing a loss of control over cerebral blood flow. as the brain swells, intracranial pressure rapidly rises. the brain can herniate, and the brain stem can fail within five minutes. except in boxing, all cases have occurred in athletes under age 20. due to the very small number of documented cases, the diagnosis is controversial, and doubt exists about its validity. a 2010 pediatrics review article stated that there is debate whether the brain swelling is due to two separate hits or to just one hit, but in either case, catastrophic football head injuries are three times more likely in high school athletes than in college athletes. epidemiology annual incidence of mtbi by age group in canada most cases of traumatic brain injury are concussions. a world health organization (who) study estimated that between 70 and 90% of head injuries that receive treatment are mild. however, due to under reporting and to the widely varying definitions of concussion and mtbi, it is difficult to estimate how common the condition is. estimates of the incidence of concussion may be artificially low, for example, due to under reporting. at least 25% of people with mtbi fail to get assessed by a medical professional. the who group reviewed studies on the epidemiology of mtbi and found a hospital treatment rate of 1–3 per 1000 people, but since not all concussions are treated in hospitals, they estimated that the rate per year in the general population is over 6 per 1000 people. age young children have the highest concussion rate among all age groups. however, most people with a concussion are young adults. a canadian study found that the yearly incidence of mtbi is lower in older age groups (graph at right). studies suggest males develop mtbi at about twice the rate of their female counterparts. however, female athletes may be at a higher risk of sustaining a concussion than their male counterparts. sports up to five percent of sports injuries are concussions. the u.s. centers for disease control and prevention estimates that 300,000 sports-related concussions occur yearly in the u.s., but that number includes only athletes who lost consciousness. since loss of consciousness is thought to occur in less than 10% of concussions, the cdc estimate is likely lower than the real number. sports in which concussion is particularly common include american football, the rugby codes, mma and boxing (a boxer aims to "knock out", i.e. give a mild traumatic brain injury to, the opponent). the injury is so common in the latter that several medical groups have called for a ban on the sport, including the american academy of neurology, the world medical association, and the medical associations of the uk, the us, australia, and canada. workplace concussions may also be common and occur in the workplace. according to the us bureau of labour statistics, the most common causes of mtbi-related hospitalizations and deaths from the workplace are falls, force of heavy objects, and vehicular collisions. as a consequence, jobs in the construction, transportation, and natural resource industries (e.g. agriculture, fishing, mining) have more elevated mtbi incidence rates ranging from 10 to 20 cases per 100,000 workers. in particular, as vehicular collisions are the leading cause of workplace mtbi-related injuries, workers from the transportation sector often carry the most risk. despite these findings, there still remain important gaps in data compilation on workplace-related mtbis, which has raised questions about increased concussion surveillance and preventive measures in private industry. history the hippocratic corpus mentioned concussion. the hippocratic corpus, a collection of medical works from ancient greece, mentions concussion, later translated to commotio cerebri, and discusses loss of speech, hearing, and sight that can result from "commotion of the brain". this idea of disruption of mental function by "shaking of the brain" remained the widely accepted understanding of concussion until the 19th century. in the 10th century, the persian physician muhammad ibn zakarīya rāzi was the first to write about concussion as distinct from other types of head injury. he may have been the first to use the term "cerebral concussion", and his definition of the condition, a transient loss of function with no physical damage, set the stage for the medical understanding of the condition for centuries. in the 13th century, the physician lanfranc of milan's chiurgia magna described concussion as brain "commotion", also recognizing a difference between concussion and other types of traumatic brain injury (though many of his contemporaries did not), and discussing the transience of post-concussion symptoms as a result of temporary loss of function from the injury. in the 14th century, the surgeon guy de chauliac pointed out the relatively good prognosis of concussion as compared to more severe types of head trauma such as skull fractures and penetrating head trauma. in the 16th-century, the term "concussion" came into use, and symptoms such as confusion, lethargy, and memory problems were described. the 16th century physician ambroise paré used the term commotio cerebri, as well as "shaking of the brain", "commotion", and "concussion". guillaume dupuytren distinguished between concussion and unconsciousness