Date Published: March 21, 2018
Publisher: Public Library of Science
Author(s): Yi-Lang Chen, Ying-Cen Mu, Riccardo Di Giminiani.
Data regarding the effects of backpack carriage on children’s body strains while walking are limited. This study measured the body posture, muscle activation, and subjective discomfort scores of 12 male schoolchildren (age: 12.3 (range 12.1–13.0) y, height: 151.3 (range 144.2–154.6) cm, weight: 46.6 (range 43.6–49.7) kg) carrying backpacks weighing 5%, 10%, and 15% of their respective body weights (BWs) and walking for 10 min on a treadmill. For each load, three positions along the spinal column (T7, T12, and L3) were examined. Participants carrying a backpack weighing 15% of BW exhibited higher head flexion, trunk flexion, and corresponding muscle activation, and a lower lumbosacral angle compared with those carrying loads of 5% and 10% of BW. The waist received the highest discomfort scores when the backpacks were carried at the L3 position. Conversely, the discomfort rating for the neck and shoulders where the highest when the backpack was at the T7 position; this high backpack position also caused more head flexion than the other two positions. For the musculoskeletal health of children, the findings suggest that carrying a school backpack weighing 15% of BW should be avoided, and carrying at the T12 position may be recommended for schoolboys.
Most schoolchildren in developed countries carry backpacks. Previous studies have demonstrated that daily physical stresses associated with carrying backpacks cause significant forward lean of the head and trunk [1–3] and changes in spinal curvature [4,5]. Neuschwander et al.  found that an increase in backpack load significantly compresses lumbar disc heights measured in the midline sagittal plane. Daily intermittent postural adaptations are assumed to result in pain and disabilities in schoolchildren [7–9].
The results of previous backpack studies lack uniformity in examination of posture alteration and muscle activation, particularly with regard to the weight carried and the position of the weight. Reasons for the lack of uniformity may be differences in participant groups (children vs. adults), testing protocols (dynamic or walking vs. static or standing), or assessment indices (biomechanics, physiology, and psychophysics). To understand the most common backpack problems in schoolchildren, this study investigated body posture, muscle activation, and subjective discomfort scores in male schoolchildren who walked for 10-min periods carrying backpacks with various weight and position combinations.
This study required participants to carry backpacks weighing 5%, 10%, and 15% of their total BW and walk for 10 min on a treadmill. Each carrying weight was also investigated at three backpack positions. The results show that differences in head and trunk flexion and lumbosacral angle between the no-backpack condition and carrying a load weighing 15% of BW were significant in comparison with differences between the other observed loads. Positioning the backpack near the T12 position may avoid extreme discomfort at the body sites investigated. This study suggests that carrying a load weighing no more than 10% of BW at the T12 position may be acceptable for schoolboys.