A study was performed by NIOSH to determine whether professional football players in the National Football League (NFL) had an increased risk of dying prematurely compared to the general population. A study group of 6,848 former NFL players was found to have a death rate 46% less than the general population, with a reduced risk of death by violence, accidents, and cancer. However, NFL players who were offensive or defensive linemen had a significantly increased risk of death by heart disease; players in the largest body size category, 64% of all linemen, had a six times greater risk of heart disease than those of normal size. An increased incidence of nervous system disorders was noted in former NFL players, including four who died of Lou Gehrig's disease. NIOSH recommends that players have regular medical checkups and be aware of heart disease during and after retirement in order to prevent the disorder.