Operation overload: Kids' backpacks.

At least once a week, more than a third of middle-school children carry loads on their backs in excess of 30 percent of their body weight, Italian researchers report in the Dec. 4, 1999 LANCET.

A study of 237 sixth-graders in Bresso, near Milan, found an average backpack load of 20 pounds, which equaled 22 percent of the body weight of the children carrying it, says study coauthor Stefano Negrini, a rehabilitation specialist at the Don Carlo Gnocchi Foundation Hospital in Milan.

This average load would equal a burden of 39 lb for a 176-1b man and 29 lb for a 132-1b woman.

Moreover, 35 percent of the children at least once a week carried loads that would equal 48 lb and 36 lb for average-size men and women, respectively, Negrini and his colleagues calculate. The researchers earlier had presented findings that more than 60 percent of children in this age group had experienced back pain more than once due to heavy loads.

"Rates of low-back pain in children are approaching those seen in adults," Negrini and this colleagues note. "The lack of certified limits for backpack carrying is shortsighted."

Backpack weight should be reduced, but more study is needed before authorities can set specific limits, Negrini concludes.