Backpacks (BP) represent the method most used by students to transport external cargo. Previous studies cite that between 4.7% and 38% of children carry daily BP loads greater than 20% of their body mass. The purpose of this study was to analyze spatiotemporal parameters of gait in children using varyingly loaded BPs.

This study examined 231 schoolchildren (118 boys, 113 girls) aged six to 12 years, carrying a traditional BP to manipulate loading (Crossing Backpack Children Arpenaz 7 Litres, Junior Red Quechua). The inclusion criteria were: age between six and 12 years, no pain in the lower limb and back at the time of examination. The exclusion criteria were: recent injury to the lower limb and back, alterations in the foot bones, congenital structural changes to the ankle, flatfoot associated with cerebral palsy, surgical treatment of foot or lower leg, or any genetic, neurologic or muscular conditions.

The parents were provided with information about the study, and those consenting for their children to participate, also completed a questionnaire. The children were fully informed of the procedures involved and gave assent. All procedures were in accordance with the ethical standards of the institution of University of Malaga (CEUMA 91/2016H) and with the 1964 Helsinki declaration.

Load was added to the BPs in increments of 5%, 10%, 15% and 20% of the child's body weight. Spatio-temporal parameters were measured with the OptoGait® system.

Two examiners were responsible for the system software and collecting data. General information, including height and weight, were recorded. To measure gait parameters, the protocol used for the Optogait reliability testing was used. This involved the children walking on a walkway at a comfortable speed, repeating this walk three times and calculating the mean speed. Prior to data collection, the children performed one familiarization trial for five minutes. Children were asked to walk naturally, facing forward, with their hands out of pockets; wearing light, comfortable clothes, with the BP placed correctly. As the children started walking, the researchers selected the foot of the first step inside the bars, in the Optogait software. After being instructed to 'walk slowly at a comfortable speed', the children walked from a point two metres in front of the bar and stopped at a point two metres behind the last bar, to minimize effects of acceleration and deceleration

Inclusion Criteria:

• The inclusion criteria were: age between six and 12 years, no pain in the lower limb and back at the time of examination.

Exclusion Criteria:

• The exclusion criteria were: recent injury to the lower limb and back, alterations in the foot bones, congenital structural changes to the ankle, flatfoot associated with cerebral palsy, surgical treatment of foot or lower leg, or any genetic, neurologic or muscular conditions.

6 to 12 years

The study was a double-blind, five-arm experimental study. This biomechanical study was designed to examine the effect of weight in the gait of the children with the backpack, no follow-up was undertaken.

A convenience sample of children was approached The potential recruits are asked to attend a screening appointment Children were asked to walk naturally, facing forward, with their hands out of pockets; wearing light, comfortable clothes, with the BP placed correctly with 5 different weights inside the backpack.