Humans in Work System Environment - Fundamentals and Assessment Tools for Occupational Ergonomics - page 91

According to the work system approach, different influences of work environment affect a working
person (Figure 5.15). These influences hardly ever appear isolated, but mostly in combination
(Section 5.3.2). Concerning heat work, for example, unfavorable climatic conditions take effect in
combination with hard dynamic muscle work (Luczak, 1979). In doing so, the climate conditions are
allocated to environmental influences of a work system, whereas, muscle work is considered as an
action resulting from the work task.
The subjects of investigation concerning heat work are the questions, which “human subsystems” are
especially loaded, how these loads interact, and when “bottlenecks” arise in the human body. For
example, the cardiovascular and the muscle system cooperate, because the amplitude and the frequency
of respiration depend on the muscular load. In the same way, the cardiovascular and the metabolic
system depend on each other due to the perspiration under heat work conditions — that is, an increasing
loss of water and salt — these materials urgently have to be taken in. Therefore, interferences caused by
salt deficiency (e.g., heat convulsions, which effect the cardiovascular system and, therefore, also the
muscle system) can be anticipated.
At the time of publication of the following described study (Luczak, 1979), numerous scientific realiz-
ations were present concerning “pure” muscle work and especially the endurance limit and the recovery
time. However, combinations with environmental influences were examined only sporadically, referring
to a few points of the entire load continuum.
A goal of the investigation was the obtaining of physiologically justified realizations for the determi-
nation of recovery time for heat work. These realizations should cover a wide range of relevant load con-
tinuums. In addition recovery times should be assigned to measurable load values.
The general objective of the investigation is based on the following partial goals:

. Development of a model for the coupling of the thermal regularization system and the cardio-
vascular system
. Examination of the model on the basis of individual results from the literature
. Determination of recovery times and the superposition principles of energetic effects and climatic
loads in the fast-time-simulation based on the model

metabolic system
(O 2 and nutrition converting)

cardiac circulatory
system
(transport system
and heat balance)

e.g.

spine
(carrying of loads
and parts of the body)

climate,

substances

muscles & tendons

bones & joints

l r f a

FIGURE 5.15 Physical subsystems of humans and influences on these subsystems.