it found that there are more than 80% of the
sample sizes carried the heavy school bags which
weight more than 10% of the body weight. The school
bag carrying is one of the tasks in school activities
which can effect the spine shape [2] if this task is assign
to be a heavy workload. The carrying weight was
recommended to be at 10% of the student body weight
which was set as an acceptable safety level [3] [4] [5].
Commonly in Ergonomics Design any workload assign
was set by comparing to the subject strength. In healthy
person, the amount of strength which is directly relative
to the number of muscle cells can be measured by the
body weight. Nevertheless, there was a report about a
change in Thai children proportion. Ministry of Public
Health of Thailand reported that the present Thai
children have been overweight [6]. Since the
overweight in children may be caused by the fat cell,
the body weight should not be relative to the body
strength. Therefore body weight in Thai primary
students may not use as an indicator to assign the
school bag weight. The first objective of this research is
to find the relationship between the primary student
strength and their body weight. The second objective is
to evaluate the school bag carrying task based on a
biomechanical static model. This task was compared
the compressive force on the lower back to the
individual composite strength capacities.