On a chilly winter morning, dozens of truck driver trainees file into a classroom at the headquarters of Prime Inc., a trucking company based in Springfield, Mo.
At the front is Siphiwe Baleka, an energetic former swimming champion in his mid-40s. He delivers grim news about trucker health to the new recruits.
"If you haven't started to think about this, you need to start right now," Baleka says. "You are about to enter the most unhealthy occupation in America."