The heavy physical training elite athletes endure may prime the brain for addiction. According to a study from Tufts University, an extreme preoccupation with training can mimic the biological effects of drug abuse, leading to withdrawallike symptoms such as anxiety and depression when the exercise stops. Exercise releases the body's natural opioids, endorphins, and has long been touted for relief of stress, anxiety and depression.FILE In this March 26, 2013, file photo, linebacker Manti Te'o runs the 40 yard sprint during Notre Dame's NFL football pro day in South Bend, Ind. Some analysts have Notre Dame's AllAmerican linebacker Mante Te'o back to being a firstround cinch, even after a great season was marred by a poor game against Alabama followed by the hoax involving a deceased "girlfriend." He did not perform well at the NFL combine but did better at pro day in South Bend. Te'o is one of the people to watch for during the threeday NFL draft beginning Thursday, April