Effects of backpack carriage on foot–ground relationship in children during upright stance
Introduction
Primary school represents the first time in life where human beings are required to carry a load to perform their daily activities. In most cases, this task is efficiently accomplished by means of a backpack, due to its popularity among the population of schoolchildren.
Nevertheless, in recent times a number of doubts and concerns have been raised by parents, school professionals and researchers about the possible consequences of what appears as a constant increase in backpack weight.
It is noteworthy that early investigations carried out in the 1960s (to assess energy expenditure and postural alterations) reported a schoolbag average weight in the range of 2.26–3.2 Kilograms (Kg) [1], while a number of recent studies performed in Europe, North and South America and Oceania [2], [3], [4], [5], [6], [7] showed that for 6–13-year-old children, the average weight of a backpack, has risen to values in the range of 4–9 Kg. In the last decade many researchers investigated the possible consequences originated by excessively loaded backpacks from a multidisciplinary point of view, by means of epidemiological, physiological and biomechanical studies [8]. As regards the latter, it has been demonstrated that trunk forward lean, craniovertebral angle and gait patterns may be significantly altered by load carriage [9], [10], [11], [12], [13], as well as balance indicators such as postural sway [14].
On the other hand, less attention has been paid to understanding how backpack carriage acts on the foot–ground relationship in terms of contact area and plantar pressure distribution. In fact, to the authors’ knowledge, only one study has been carried out on this topic [15] with results that showed a substantial increase in center of pressure (COP) displacements when the backpack/body weight ratio exceeded 10%. On the contrary, no modifications of plantar force distribution were found.
Backpack effects on foot structure and functionality have instead been investigated on adult subjects, in particular soldiers [16]. This is not surprising if one considers that the backpack represents an essential element in performing most military tasks and the combination of ‘high loads–high exposure time’ (which is typical for example of troops on the march) is often a source of foot problems, which range from simple foot blisters to more serious metatarsalgia or stress fractures. Moreover, it is hypothesized that mechanical overloading on the foot, and the consequent altered plantar pressure distribution, especially in the midfoot region, may play a role as a co-factor in plantar fasciitis onset [17].
On the basis of the aforementioned considerations, this study intends to investigate the effect of backpack carriage in primary school children from the point of view of possible modifications occurring in the foot-to-ground relationship. In particular, data were acquired from two series of trials (with and without backpack) by means of a pressure platform under realistic conditions (i.e. directly at school on regular school days), and then post-processed to assess changes in static foot–ground contact area, pressure distribution patterns and COP displacements, with respect to the reference unloaded condition. The results, although restricted to the quiet stance condition, should contribute information useful in effectively managing the possible negative consequences of excessive load carriage, especially in a crucial stage of a child's physiological development.
Section snippets
Experimental procedure
A total of 570 requests for participation, containing a detailed description of the purposes of the study and the experimental protocol, were delivered to all the pupils enrolled in three primary schools of the city of Cagliari (Italy). Of these, 447 families (corresponding to 231 male and 216 female subjects, Table 1) expressed formal acceptance by signing an informed consent form.
All the experimental tests were randomly performed on regular school days in the period May–June 2009. Children
Foot–ground contact area
A preliminary screening of the foot–ground contact maps revealed that in many cases the contact area related to children's tiny toes was so small that the corresponding applied pressure was virtually undetectable; this would make the analysis non-homogeneous as the actual contact area may be underestimated when the toes are either partly or entirely not visible. Thus it was decided to express the contact area as the sum of the three sub-regions (forefoot, midfoot and rearfoot) excluding any toe
Foot–ground contact
Up to now, plantar pressure measurements on healthy children have usually been performed to assess the evolution of foot structure to complete physical maturity and to compare pressure patterns with those of adults. Generally speaking, children exhibit significantly reduced peak pressures under dynamic conditions [19], [20], especially in toes and forefoot. The results of the present study, which refer to quiet stance, can be directly compared with those obtained by Cavanagh et al. [18], who
Conclusions
Since the early years of primary school, children are often required daily to carry loads that can be considered excessive according to the many studies which establish a threshold for the maximum allowable load in the range of 10–15% of body weight. Among the possible consequences of this activity, there are alterations of the physiological foot–ground relationship which have so far been scarcely explored. The results of the present study, performed on primary school children, showed
Conflict of interests
None of the authors has any conflict of interest.
Acknowledgements
The authors wish to thank the Directors of the schools involved in the research (Prof. Maria Marcella Vacca and Prof. Valentina Savona) and the teacher Enrica Collu for their invaluable support in the organization of test sessions. The help provided by Ms. Elisa Priolo in postural and anthropometric data acquisition was also greatly appreciated.
References (35)
- et al.
Backpack as a daily load for schoolchildren
The Lancet
(1999) - et al.
Schoolbag weight and musculoskeletal symptoms in New Zealand secondary schools
Applied Ergonomics
(2005) - et al.
Changes in gait patterns in 10-year-old boys with increasing loads when walking on a treadmill
Gait & Posture
(2000) - et al.
Gait and posture responses to backpack load during level walking in children
Gait & Posture
(2003) - et al.
Load carriage using packs: a review of physiological, biomechanical and medical aspects
Applied Ergonomics
(1996) Plantar pressure distribution during barefoot standing, walking and landing in preschool boys
Gait & Posture
(2001)- et al.
Effects of fatigue and load variation on metatarsal deformation measured in vivo during barefoot walking
Journal of Biomechanics
(2002) - et al.
Comparison of ground reaction forces between obese and control young adults during quiet standing on a baropodometric platform
Gait & Posture
(2003) - et al.
Effects of varying backpack loads on peak forces in the lumbosacral spine during walking
Clinical Biomechanics
(1998) - et al.
Carrying of school bags by children
Ergonomics
(1965)