Wearing a heavy backpack can significantly decrease blood flow through your shoulder, down to your fingertips, and could result in the loss of some fine motor skills as well as increased fatigue, according to new research.

Adults wearing backpacks with loads of 26 pounds for just 10 minutes experienced an almost 50 percent decrease in blood flow through large and small vessels in their upper bodies in a study conducted by the University of California, San Diego’s department of orthopaedic surgery.

The study was expected to be presented Monday at the annual meeting of the American Physiological Society, during the Experimental Biology 2008 scientific conference, in San Diego.

Backpack straps typically rest over the area of the body where the axillary vein is located. If the vein gets compressed, it causes abnormally high blood pressure inside the veins and a subsequent decrease of blood flow in the shoulders and arms.

Last year, the same researchers concluded that backpack straps can obstruct blood flow and contribute to shoulder fatigue in children when the load they are carrying is as little as 10 percent of their body weight. The team then decided to look at the effects of backpack weight on adults, because in some professions, like the military, firefighting and mountain rescue, the packs weigh as much as 60 percent of the adult’s body weight.

“We think that backpack straps may benefit from a redesign that skirts the vein leading from the upper extremity to the heart,” first author of the study, Dr. Timothy Neuschwander, said in a prepared statement.

His team examined eight healthy volunteers, six men and two women between the ages of 18 and 30. Baseline flows were measured immediately before and 10 minutes after donning a 26-pound backpack.

(Source: American Physiological Society, news release, April 7, 2008)