Dr. Sabrina Polletta says because of the COVID-19 pandemic, many school-age children are carrying around more on their backs than usual.
"We don't always have a lot of control over the weight because with COVID, a lot of the schools, what they're doing is making the kids lug back and forth as much material as possible in case overnight a class will close," she told CBC's Let's Go.
"So I've seen in the last year and a half that children's backpacks are fuller than they used to be because of what we're living through now."
Polletta said that the recommended weight for a child's backpack is actually between 10 and 15 per cent of a child's body weight.
"The weight is an important factor not to put too much stress on their little backs," Polletta said.
For high school students, this could go up to 25 per cent of their body weight.
Polletta said that beyond weight, size is a factor as well.
She said a kid's backpack shouldn't be wider than their torso and it shouldn't hang lower than ten centimetres below their waist.
"It can't hang too low to start off with because when you fill it, it will hang even lower and put pressure on the shoulders, the neck, the back," she said.
A good backpack should also have padded, adjustable straps.
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When it's not possible to follow these recommendations, Polletta said parents can try to ease the burden of a heavy backpack when possible.
"If you can't get around it, because they have to be carrying all these books because of the COVID situation we have now, I would say limit the amount of time that this weight is on their back."
She suggested helping a child carry their backpack to the car if they are being picked up, or instructing them to put it down before going to play with friends in the schoolyard.