The use of trollies and backpacks for load carriage in elementary school studentsa biomechanical analysis and recommendations

Resum

Every day, children carry a backpack full of books to school. This International Doctoral Thesis evaluates the kinematics changes whilst carrying a backpack or pulling a trolley with different loads, in elementary school students. In study I was evaluated the spatiotemporal gait parameters in 14 children from 6 to 12 years old. The experimental conditions analysed were walking without a trolley, and pulling a trolley with 10%, 15% and 20% of the % BW. The load conditions were completed in a randomized order, and children walked for 5 trials per condition along 15 meters of walkway. A pressure platform was placed in the middle of the walkway. The variables analysed were velocity (m/s), cadence (steps/s) and stride length (m); swing phase, stance phase, single support phase and double support phase that were expressed as a % GC. Compared with unloaded walking, the three load conditions analysed produced a significant decrease in swing phase and single support phase (p<0.001), and a significant increase in cadence (p=0.019), stance phase and double support phase (p<0.001). Study II was focused on comparing the effects of carrying a backpack and pulling a trolley, both with the 15% BW on gait kinematics for 53 students. The variables analysed were; velocity (m/s), cadence (steps/s) and stride length (m), that were normalized. In addition, swing phase, stance phase, single support phase and double support phase were measured and expressed as a % GC. In addition, average and standard deviation (in degrees) of sagittal, frontal and transverse planes were computed for thorax, pelvis, hip, knee and ankle. As results, no significant differences were obtained in spatiotemporal gait parameters between pulling a trolley and control. Study III analysed the kinematic gait adaptations associated with pulling a school trolley with different loads and the effects of the type of packing device user (backpack vs. trolley) and body side (loaded vs. unloaded) in a group of 53 students from an elementary school. Averages and standard deviations of spatiotemporal gait parameters and 3D kinematics of the lower limbs and thorax were obtained for the loaded and unloaded sides of the body while children pulled the trolley with 10%, 15% y 20% BW. Spatiotemporal gait parameters were affected by pulling a trolley with a load of 20% BW, although the changes were not important. In the 3D kinematics analysis, the main effects of trolley load were observed in the thorax, with increased flexion as the load increased, and in the pelvis between baseline and 10– 15% BW. No interaction was found between kinematic parameters and the type of packing device used (trolley or backpack). Considering the loaded and unloaded sides of the body, the transverse plane of the thorax was the main site affected by the asymmetrical task. In study IV, the complete gait kinematic waveforms of the thorax, pelvis, hip, knee and ankle of the 49 participants were analysed while carrying a backpack and a trolley loaded with 10, 15 and 20% BW to clarify recommendations for appropriate load carriage in children. The variables obtained in each condition were the degrees of flexion/extension, adduction/abduction and internal/external rotation of thorax, pelvis, hip, knee and ankle. Statistical parametric mapping (SPM) was used to evaluate differences between conditions and loads throughout the gait cycle. The results from the analysis of the different backpack conditions showed that the magnitude of the differences decreased from proximal to distal joints compared to the control condition. While the increased load in the school trolley only required minor kinematic adaptations compared to unloaded walking. Study V was aimed at determining whether carrying a backpack and pulling a trolley with different loads influenced the variability in the rating of perceived exertion (RPE) and gait asymmetry (GA) that children reported. A 3D motion capture system was used to analyse the spatiotemporal gait variables. The ratios, symmetry angles and gait asymmetry of the step length, swing time, and stance time were subsequently analysed. The RPE was recorded at the end of each walking trial. The results demonstrated that none of the asymmetry parameters showed significant differences while carrying the backpack and pulling the trolley. The RPE data increased from the control to the 20% BW (p<0.05) and from the 10% BW to the 20% BW backpack condition (p<0.05). As a general conclusion, more than half of the schoolchildren (56.9%) were found to carry more than 15% BW, school trolleys being the chosen option by 64% of girls. Besides, school trolley users seem to feel a higher positive perception of fatigue and weight perception than backpack users. With respect to the kinematic adaptations, the use of the school trolley between 10% and 20% BW seems to let schoolchildren maintain a closer posture to unloaded walking with a lower perception of effort than the use of the school backpack. The results of the kinematic analysis suggest children avoid loads greater than 10% when carried in a backpack, or greater than 20% if using a trolley, to maintain unloaded over ground walking kinematics.