Professional football is among the most violent sports on the planet. Tall, thick men who weigh more than 200 pounds regularly collide at high speeds, resulting in shots to their bodies that would knock the average person out cold. Yet, these guys get up and do it again---and again---for years, causing lasting physical and mental injuries with implications we just now are beginning to understand. To further that understanding, a group of active NFL players announced yesterday that they will donate their brains and spinal cord tissue to a Boston University medical school program that studies sports-related brain injuries, according to ESPN. The study already had commitments from 150 former athletes, including 40 retired NFL players, but never before had active players signed on. The players---Baltimore Ravens center Matt Birk, Seattle Seahawks linebacker Lofa Tatupu, and Arizona Cardinals receiver Sean Morey---will be interviewed annually for the rest of their lives, allowing the researchers to track the relationship between clinical symptoms and pathology. Morey says he decided to get involved after reading about former CU football star and New England Patriots linebacker Ted Johnson, a player who took many shots to the head over a 10-year NFL career. Johnson's injuries and subsequent life problems were profiled by 5280's Robert Sanchez in the August 2009 edition of the magazine, in a feature that details just how devastating repeated shots to the head can be. Players regularly suffer long-term effects like depression, memory loss, and wild mood swings, but some injuries are fatal. Since 2002, five NFL players have died or committed suicide following years of rapidly declining mental health, Sanchez reported.