Sport Sci Health (2008) 4:7–14 DOI 10.1007/s11332-008-0060-8 Abstract Fifteen male high school students (12.5±0.5 years) voluntarily participated in this study. They carried backpacks with 0 (as a control group), 8, 10.5 and 13% of their body weights on a treadmill at 1.1 m/s for 15 min. Their systolic (SBP) and diastolic (DBP) blood pressure was measured by a digital blood pressure me- ter, and heart rate (HR), minute ventilation (MV) and res- piratory frequency (RF) by a Gas Analyzer System, in 3 positions: rest, exercise (15 min walking) and recovery (3 min after walking). The results indicated that the SBP and MV during and 3 min after carrying backpacks 10.5 and 13% of body weight were significantly higher than under 0 and 8% body weight load conditions. The DBP increased significantly only at the 13% body weight load condition, after 15 min of walking. The weight of school backpacks for high school students can be recommend- ed as 8% of their body weight, because carrying 8% body weight load did not significantly change cardio-respira- tory parameters. Key words School students · Walking · Backpack · Cardio-respiratory parameters Introduction Students in primary, secondary and tertiary education commonly use backpacks to carry their books and sport- ing equipment on a daily basis [1, 2]. The backpack is one of several forms of manual load carriage that pro- vides versatility and is often used by hikers, backpackers and soldiers, as well as school children [3]. The backpack is an appropriate way to load the spine closely and sym- metrically, while maintaining stability [4]. However musculoskeletal problems associated with backpack use have been causing increasing concern with school children [2, 5]. There are also a few reports of other problems associated with backpacks i.e., functional scoliosis and rucksack palsy [6], reduced lung function [5, 7, 8] and increased metabolic costs [3, 9–11]. The combined effects of heavy load, position of the load on body, size and shape of the load, and load distribution, time spent carrying and physical condition of the indi- vidual were hypothesised as factors associated with these problems. Concerns associated with backpack use among today’s school children and adolescents have recently been raised. The presence of back discomfort, negative postural changes and potential injury associated with the transport of heavy backpacks are now increasingly prevalent [6]. ORIGINAL ARTICLE Received: 5 September 2008 / Accepted: 15 November 2008 © Springer-Verlag 2008 Effect of carrying school backpacks on cardio-respiratory changes in adolescent students H. Daneshmandi · F. Rahmani-Nia · S.H. Hosseini H. Daneshmandi () Sport Injuries and Corrective Exercise Faculty of P.E and Sport Sciences Guilan University Rasht, Iran e-mail: Danesh@Guilan.ac.ir F. Rahmani-Nia · S.H. Hosseini Sport Physiology Faculty of P.E and Sport Sciences Guilan University Rasht, Iran