Boston -- Can those backpacks your kids wear each day to school affect their health?

Here's a statistic that may not surprise you...more than 92% of the children in the U.S. carry backpacks. And typically, those backpacks are loaded with books, supplies and other stuff that are nearly one-fourth, or 22%, of the child's body weight. Researchers say that heavy load can put a strain on kids, with the straps significantly increasing pressure when the load is 10% or more...

Researcher Doctor Tim Neuschwander at the University of California in San Diego says these backpacks can get too heavy...He says these loads can obstruct localized blood flow, and contribute to shoulder fatigue.

Neuschwander says it's time for designers to build a better backpack...

Backpack straps typically rest on an area of the body where they may compress the axillary vein which causes abnormally high blood pressure inside the veins, and a subsequent decrease of blood flow in the shoulders and arms. The researchers say backpacks that are too heavy, with straps that convey too much pressure can restrict vascular blood flows, and may result in the loss of fine motor control and increased fatigue.