Soldiers and Marines in Iraq and Afghanistan routinely carry between 60 and 100 pounds of gear including body armor, weapons and batteries.
The heavy loads shouldered over months of duty contribute to the chronic pain suffered by soldiers like Spc. Joseph Chroniger, who deployed to Iraq in 2007.
Twenty-five years old, he has debilitating pain from a form of degenerative arthritis and bone spurs. "I mean my neck hurts every day. Every day," he says. "You can't concentrate on anything but that because it hurts that bad."