Our school days are supposed to be the happiest of our lives, however a new study has found that they may also be some of the most painful.

Portuguese scientists looked at almost 140 young people aged 12-15 to determine the effect of poorly designed school furniture and heavy school bags.

They found that chairs that are too small, desks that are too low and schoolbags that are too heavy are contributing to chronic back pain in teenagers.

According to the findings, almost two in three of the students suffered from some type of back pain. This was more likely if there were big differences between desk height and elbow height. This desk height discrepancy was more often found in girls than boys.

"These results highlight the importance of studying the school environment to establish preventive programmes for back pain in youths," the scientists from the University of Lisbon said.

They pointed to big increases in recent years in the number of school-going children who often report back pain, neck pain and headaches.

They also noted that people who suffer back pain during childhood are at an increased risk of suffering from it as an adult as well, unless it is treated properly.

The scientists acknowledged that there are many risk factors for back pain, including age, lifestyle, family history and stress. However, they insisted that ergonomic factors, such as the type of desk a person sits at, also play a major role.

They added that children today spend more and more time in school sitting at desks and less time doing physical activity.

"These results highlight how relevant it is to study the school environment in order to establish preventive programs for back pain in children and adolescents, not only health wise, but also in terms of school education," the team said.

Details of these findings are published in the journal, Human Factors and Ergonomics.