Civil Engineering Reference
In-Depth Information
12
Physical Workload and Heat Stress
12.1
INTRODUCTION
In most Western countries, physical workload is no longer as common as it used to be. In
manufacturing, hard physical labor has been taken over by materials handling aids,
mechanized processes, and automation. Legislation has also put limits to the amount of
workload that employees can be exposed to. Yet, in some occupations such as
construction work, commercial fish netting, and logging, workers still perform much
physical work. Such work generally involves less structured tasks, and they are difficult
to mechanize.
Physical work activities are still common in industrially developing countries where
mechanization has yet to pay off in the light of easily available labor. For example, in the
construction industry materials are typically carried by workers. Eriksson (1976)
estimated 30 years ago that 200 workers at a road construction site in Bangladesh could
move as much dirt manually as one Caterpillar, and the costs were equivalent. Under
such circumstances, the national economy, as well as the workers' personal economy,
will gain by using manual labour.
Although the physical work demands in manufacturing have been substantially
reduced, there are still many situations which require ergonomic analysis. Many
individuals are less capable of physical work, and in this chapter we are particularly
interested in individual differences due to gender and age.
12.2
METABOLISM
Metabolism is defined as the conversion of foodstuffs into mechanical work and heat
(Astrand, Rodahl, Dahl, and Stromme, 2003). In order to be useful to the body, the
foodstuff is converted into a high-energy compound
adenosine triphosphate
(ATP). ATP
serves as a fuel transport mechanism. It can release chemical energy to fuel internal work
in the various body organs. The phosphate bond can easily be broken down to
adenosine
diphosphate
(ADP) according to the following formula:
ATP+H
2
O=ADP+energy release
This basic reaction supplies the energy for the muscle cells. After the energy has been
delivered the ADP is restored again to ATP using a combination of foodstuffs. At first
glucose is used (if available), then glycogen, and finally fats and protein.
During continuous work there is oxygen available in the blood. This oxygen is used
for the conversion, so that each molecule of glucose will generate 36 molecules of ATP.
