Trunk muscle activity in different modes of carrying schoolbags.

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Ergonomics. 2006 Feb;49(2):127-38.

Trunk muscle activity in different modes of carrying schoolbags.

Motmans RR, Tomlow S, Vissers D.

Product Ergonomics Research Centre, Katholieke Hogeschool Limburg,

Belgium.

The daily load of carrying schoolbags is influenced by the mode of

carriage. Electromyographic (EMG) activity from rectus abdominis and

erector spinae was recorded bilaterally in five static conditions: no

bag; shoulder bag; backpack; front pack; double pack. Nineteen

students carried a load of 15% of their body weight. A double pack,

with the load equally distributed in a front and a backpack, showed

no significant differences in EMG activity compared with unloaded

standing. The activity levels of erector spinae significantly

decreased while carrying a backpack and increased with a shoulder bag

and a front pack. Rectus abdominis revealed significantly higher EMG

levels in the backpack trial. Asymmetrical activity between the right

and the left part of the back muscles was clearly observed while

carrying a shoulder bag with the weight at the right side of the

body. The abdominal muscles revealed a slightly significant asymmetry

for the shoulder bag and, surprisingly, also for the backpack. These

findings suggest that the physical stresses associated with carrying

book bags can be minimized by the design of a double pack. Asymmetry

in muscle activity may indicate a failure of trunk stabilization and

contribute to the development back pain.