Oh, my aching pack

Aching shoulders. Sore backs. Tired legs.

Yep, school's back in session.

As suburban children pack their books into freshly bought school bags, health officials and state educators offer a warning: Ease up.

"It's a long-standing issue. We should pay more attention to backpack injuries," said Dr. Norman Otsuka, a member of the Rosemont-based American Academy of Orthopedic Surgeons.

Two key numbers for students, parents and teachers to bear in mind: 15 and 25.

Children should not carry more than 15 percent of their body weight in a book bag, the Illinois State Board of Education cautioned in 2006. A 65-pound second-grader, for instance, should carry no more than a 10-pound bag.

However strong the child or pressing the homework assignment, backpacks shouldn't top 25 pounds, medical experts advise.

Nearly 7,500 school-age children head to emergency rooms and medical clinics annually with strained muscles and bruised shoulders caused by heavy backpack loads, according to the U.S. Consumer Product Safety Commission.

Many complaints centered on tripping over bags or getting hit by a bag, in addition to shoulder, neck and back strain, said Otsuka, of Shriners Hospital for Children in Los Angeles.

A Boston University study found eight out of 10 pre-teens schooled in the dos and don'ts of backpack safety began loading their school bags differently and felt less strain in their backs, necks and shoulders.

In the spirit of injury prevention, here goes: Lightening the load is the first step to avoiding such strain.

Carrying 15 percent of a child's bodyweight might be the threshold, but cutting back to 10 percent helps more. Still, one of every two children surveyed in an American Physical Therapy Association study carried a book bag heavier than the 15 percent benchmark.

Drop pounds by dropping books, the Illinois education agency recommended. Leave home items not needed for tomorrow's class. Prune the makeup, water bottles and sports gear that, clearly, aren't needed for sixth-period biology.

State lawmakers opted against pursuing a bill to restrict textbook size in 2003.

The type of bag and how it is worn also are integral, Otsuka said, noting that the topic has been discussed during American Academy of Orthopedic Surgeons meetings.

Messenger bags? Nope.

One-shoulder totes? Nope.

Backpacks with two padded shoulder straps are preferred, medical reports state. A padded back panel can also ease pressure.

Researchers at the University of Pennsylvania designed a bungee-cord suspended backpack to avoid the rise and fall of traditional bags with every step taken.

Rolling backpacks take the weight off the shoulders but may cause tripping and don't quite squeeze into lockers.

Still, no bag brings relief unless it's worn correctly. Just like picking up a heavy box from the floor, bend at the knees, lift with the legs and avoid excessive twisting.

"Swinging a backpack over one shoulder doesn't allow the weight to be distributed evenly and these things can cause muscle strain," Otsuka said.

Whether worn with one strap or two, backpacks, however physiologically sound, don't always pass muster with teens.

"No one my age carries backpacks," said Monica Sood, a senior at Aurora's Waubonsie Valley High School.

Sood opts instead for a shoulder bag filled with folders, notebooks and pens. Books get carried by hand, she said, a concession to the weight of her classload.

"It would be way too heavy," she said.