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."

Like many soldiers and Marines, Chroniger shouldered 70 to 80 pounds of gear daily.

A 2001 Army Science Board study recommended that no soldier carry more than 50 pounds for any length of time.

"We were doing three, four, five missions a night sometimes," Chroniger says. "You're jumping out. You're running. I mean it hurts — it hurts."