Backpacks are a better way to carry life's necessities than a briefcase or shoulder bag, especially for longer periods of time, the American Physical Therapy Association says.
But there are dangers, too. A backpack that's too heavy or improperly worn can harm joints and muscles, especially among young people.
"Typically our proximal muscles, or muscles closer to the trunk of the body, are much stronger and have greater endurance than the distal muscles, those muscles farther away form the center of the body," says Jan Richardson, president of APTA.
When a backpack is worn properly, it's supported by the strongest muscles in the body -- the back and abdominal muscles, which work together to stabilize the trunk and hold the body in proper postural alignment.
Here are some rules of thumb to follow:
Wear both straps. Slinging a backpack over one shoulder causes a person to lean to one side to compensate for the uneven weight, curving the spine. Over time, this can cause lower and upper back pain, strained shoulders and neck, and even functional scoliosis, or curvature of the spine. Teen-age girls are especially susceptible to scoliosis.
Make sure the backpack is not too heavy. Students of all ages often tote a day's worth of textbooks and a change of clothing for after-school athletics or extracurricular activities. Laptop computers are also common features in the college student's backpack.
"A backpack can range anywhere from 20 to 50 ponds -- more added weight than the average pregnant woman may have to carry," Ms. Richardson points out. Even when worn properly with both straps, leaning forward to compensate for this extra weight can affect the natural curve in the lumbar, or lower back, region.
Encourage young people to make frequent stops at their locker throughout the day to avoid carrying all their books at once, and leave non-essentials at home.
Pay attention to the type of backpack. Look for backpacks with wide straps. Narrow straps can dig painfully into shoulders as well as hinder circulation, causing numbness or tingling in the arms, which over time may cause weakness in the hands.
Even though the latest backpacks with one strap that runs across the body may be fashionable, they are not as functional because one shoulder continually bears the entire weight of the bag. It is also wise to consider the weight of the backpack when empty -- for example, a canvas backpack will be lighter weight than leather.