Schoolbags should weigh not more than 10 per cent of body weight, a study has recommended. Dr Hong Youlian of the Department of Sports Science and Physical Education at the Chinese University of Hong Kong recently conducted a survey on 'The weight of schoolbags and the meta bolic strain created in children' to determine the effects of carrying schoolbags of different weights. In the test, 15 children aged 12 walked at 1.1 metres per second for 20 minutes on a treadmill for four trials with no schoolbag, followed by tests with a school bag of 10 per cent, 15 per cent and 20 per cent of their body weight. Heart rate and the air expired were recorded before, during and until five minutes after each walk. The test results showed there was an increase in energy needed to carry loads of between 10 and 20 per cent of body weight. Based on this, it was recommended that schoolbags should be no more than 10 per cent of body weight because this load does not significantly increase the energy needed to walk.