Head injuries in sports are nothing new, but in recent years, college athletes have reported a steady rise in concussions. Football players still get the most knocks to the head. Women have managed to keep up with, and often surpass, men in sports-related concussions in the last few years. In basketball, women reported 24 percent more concussions than men did during games in the 2004-5 season. In soccer, women had concussions at almost twice the rate of men. A flurry of recent research about head injuries has called attention to the issue, but concussions remain a medical mystery. Some medical experts fear that athletics trainers are overlooking many concussions and that coaches sometimes push to get players back into games before their head injuries have healed. Recent studies have shown that concussions are cumulative: once you have one concussion, you are more likely to have a second that is more severe. As it stands, the only accepted treatment for a concussion is to rest the brain. That means no contact sports, no exercise, and no strenuous thinking, all of which creates a challenge for college athletes. Experts say that taking an important exam or memorizing the periodic table will not cause additional damage, but it will likely slow the recovery. Dr. Robert Cantu says treating an injury that cannot be directly observed is tricky, especially in a young brain, which is not fully developed until about age 22 and so takes longer to mend. He and other medical experts stress the importance of rest. However, National Collegiate Athletic Association (NCAA) guidelines leave it up to the individual trainer, suggesting that the player have no symptoms and return gradually. The Centers for Disease Control and Prevention, which recently released a primer on concussions, recommends at least one week's rest after symptoms disappear. Perhaps the biggest unknown with concussions is whether they affect long-term health. Recent news reports have detailed how several former professional players who suffered multiple concussions during their playing days have developed premature Alzheimer's disease, dementia or have been treated for clinical depression. Although some medical experts say it is too early to link concussions with long-term health problems, most people who study brain injuries do not doubt that concussions can have some lasting effect on athletes. What effects they have and who is at risk remain unclear.