Elsevier

Gait & Posture

Volume 33, Issue 2, February 2011, Pages 195-199
Gait & Posture

Effects of backpack carriage on foot–ground relationship in children during upright stance

https://doi.org/10.1016/j.gaitpost.2010.10.096Get rights and content

Abstract

Although the scientific community widely recognizes that backpack carriage in primary school children represents a critical issue, its consequences in terms of postural alterations and possible onset of musculoskeletal pathologies are still not fully understood. In particular, little information is available on the way load carriage modifies the foot–ground relationship in terms of plantar pressure distribution. This issue is of particular relevance, because the presence of a load alters the physiological weightbearing functions and, when mechanical overloading is repeated in time, it can act as a co-factor in promoting foot discomfort or pain. On the basis of these considerations, this study analyzed plantar pressure maps of 359 children attending primary schools (6–10 years old) under static upright posture conditions, to assess the magnitude and features of effects originated by load carriage on the foot–ground relationship. The collected data showed that backpack introduces significant increases in overall contact area (up to 10%) and in the plantar pressure peaks in midfoot and forefoot regions (20–30%). A significant shift in the average position of the center of pressure towards the forefoot was also observed, as an indicator of the body's attempt to restore the initial balance conditions threatened by the load. These results suggest that heavy loads, in the case of significant exposure times, may increase the risk of foot discomfort and act as a co-factor in the onset of foot structure alterations or pathologies.

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.

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