Heavy backpacks are a strain on teens' health

An Otago University study's found the average Otago teen carries 5.2 kilograms to school and back.

Another 10 percent of students carry a second two kilo bag.

Associate Professor Sandra Mandic says this is a significant issue for teenagers, with one-third saying their bag is too heavy to walk or bike to school.

She says reducing the weight could encourage more active trips to school.