It's a common sight in schools, kids overloaded with heavy backpacks that typically weigh nearly a quarter of their body weight.
Last year, University of California researchers found loads as small as 10 percent of a child's body weight can obstruct blood flow through the shoulders. Recently, the same group of researchers studied the impact of heavy backpacks on adults.
They found that even light loads of 26 pounds decreased blood flow through the shoulders and could lead to a loss in fine motor control, because the straps typically rest on an area of the shoulder that may compress the Axillary vein which is a large blood vessel that sends blood to the heart. Bottom line, encourage your kids to lighten the load.