BODY WATCH : YOUR BODY : A Heavy Load to Bear : Kids can be fashionable <i> and</i> avoid injury and strain by sizing up the right backpack.

Miguel Lope scanned the department store racks until he spied the perfect backpack: black and brown with padded shoulder straps and lots of compartments. When he returns to Hoover High School in Glendale next week, he’ll fill it with books, notebooks, pens and pencils.

What’ll it weigh?

He has no idea, but his mother, Nelly, stooping over, illustrates her estimate. “Ve-r-ry heavy,” she says with a groan.

Overstuffed backpacks are fashion statements for students from kindergarten through college. And newer designs are increasing, including compartments for bike helmets, personal computers, calculators and other necessities of modern life.

But parents worry about back pain and other orthopedic problems.

If you follow simple shopping tips and some basic carrying guidelines, orthopedic specialists say, there is little cause for concern.

Shopping Advice: “Don’t get a backpack that’s too big for the kid,” says Dr. Mauro Giordani, a Pasadena orthopedic surgeon on staff at Orthopaedic Hospital. “Look for one that is lightweight, sturdy and appropriately sized.”

Some manufacturers offer special child-size versions. JanSport, for instance, makes Kid’s Packs for youngsters ages 5-10. They are full-size packs with shorter back lengths and widths so they won’t slip so easily off the shoulders.

Manufacturers have also been striving to make backpacks more comfortable, says a spokeswoman for the Outdoor Recreation Group, another maker. Padded backs and straps are now common, as well as curved straps designed to follow body contours. Some packs have waist belts designed to stabilize the load.

“You want to have padded straps to avoid pressure on the axillary [armpit area] nerve,” says Dr. Vernon Tolo, chief of orthopedics at Childrens Hospital Los Angeles and John C. Wilson professor of orthopedics at USC.

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Loading Up: The proper maximum weight for backpacks varies from child to child because of the wide range in users’ sizes and ages, Giordani says. But if a child cannot pick up the loaded pack easily with one hand, it probably weighs too much.

Adds Tolo: Students “can carry quite a bit of weight quite safely because it is close to the body. The closer to the body, the less strain.”

(Outdoor adult backpackers aim to carry no more than one-third of their body weight, says Jim Gorman, senior editor of Backpacker magazine. “Otherwise you are over-packing.” But he notes that school backpacks are generally not as sturdy as outdoor models, and the designs vary. So the one-third rule is probably too generous for school backpacks--and not feasible for young children.)

Young veterans like Miguel go by feel. “If I start to walk like this,” he says, bending forward, “I put the overflow in my locker.”

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Caveats: Excess weight in the pack can lead to shoulder and neck pain, symptoms that parents should be aware of once school starts, Giordani says.

And, no matter how heavy or light, the weight in the pack should be distributed as equally as possible. “It’s important to balance the load,” Tolo advises. If the load is very heavy and unbalanced, it could lead to low back pain, he says, because the body will shift into unnatural postures to compensate.

Wearing comfortable shoes can help prevent orthopedic problems, too, says Giordani, who discourages the wearing of high-heeled shoes while carrying a backpack.

Whatever the backpack load, cinching the shoulder straps too tightly should be avoided because it can reduce blood circulation to the arms or push on nerves, leading to temporary numbness in the arms, Giordani says.

The one-shoulder carry, while fashionable, isn’t ideal in orthopedists’ eyes. “If a backpack is not too loaded down, it’s not a big deal,” Giordani says. “But if it is weighted down, put on one shoulder and then catawampus across the back, trapezius muscle pain could result.” The large trapezius muscle helps draw the head to one side or backward, among other functions.

Students who already have low-back pain are better off carrying a book bag, Giordani says.

* Doheny cannot answer mail personally but will attempt to respond in this column to questions of general interest. Please do not telephone. Write to Your Body, Life & Style, Times Mirror Square, Los Angeles, Calif. 90053.

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A Heavy Load to Bear

* Use padded straps to avoid pressure on the axillary nerve.

* Make shoulder straps loose to prevent pinching of nerves in the arms and reduced blood circulation.

* Carry the pack on both shoulders to prevent strain on one side of the body.

* Distribute weight in the pack as evenly as possible.

* Wear comfortable shoes to help prevent orthopedic problems.