American soldiers and marines are encountering serious problems with the weight of combat equipment they have to carry. More so than in Iraq, U.S. troops are fighting on foot. And not on the plains of Iraq, but the hills of Afghanistan. The air is, literally, thinner (less oxygen) in much of Afghanistan, which is at the same altitude as Denver, Colorado (where the thin air is a known problem for visitors).
The army and marine brass tried to reduce the weight of gear (90-100 pounds) their troops carried into battle. Of late, lighter armor, boots and other equipment took 20 pounds off. Local commanders were allowed to delete more weight. But that still meant combat troops running up those hills while wearing 50-60 pounds of stuff.
These troops are in great physical shape, which means they have the energy, muscle and determination to push themselves beyond their limits. The medics are finding themselves treating a lot of musculoskeletal problems. Knee and back problems abound, often causing much pain (especially the back spasms.) It's worse for guys who are on their second (or third) trip to Afghanistan.
Because of all this, a lot more infantry are going to retire on partial disability, and spend the rest of their lives limping around, or in constant pain. This doesn't show up in the casualty reports. But go to a veterans gathering (November 11 or Memorial Day) in 10-20 years, and you'll be able to pick out the infantry vets from Afghanistan.