Ergonomics follows a very simple basic
model that derives from physics: When you impact a body with a certain stress, the body will react with a corresponding strain.
Since a standard method causes a stress that is typical for this standard
method, the strain as a reaction to this typical stress situation should be
typical, too.
The intensity of the strain, however, is
not the same. It depends on the worker: his personal attributes, his abilities
and his skills (together they form the capability for work). And it
varies due to the actual disposition and motivation (together
called readiness for work), and his health. If the strain overruns the permanent
work load, breaks are necessary for his personal recovery to avoid
acute or chronic damage.
Most jobs
require a certain technique. Skilled persons can reach results that will never
be possible for unskilled persons.