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Physiology
 In
some respects, the body is analogous to an
automobile. In the human
machine, muscles are both cylinders and pistons, and bones and
joints are the gears. The muscles oxidize nutrients (fuel) and give
up energy, while generating metabolic byproducts (waste). Physiology
studies this process.
Two
categories of physiological demands usually are relevant during
work: static and dynamic. Static work occurs when the body is in a
stationary position for an extended period. Dynamic work involves
considerable movement.
The musculoskeletal
system is unsuited for prolonged static work because the body cannot
supply fresh nutrients to the stressed tissues. In addition, waste
products remain at the stressed site. Muscles and tendons can
inflame. Even at static loads as low as 30 percent of maximum
strength, fatigue develops rapidly.
In dynamic
work nutrients and waste products move to and from the muscles.
Consequently, the muscles can work for extended periods if the
maximum load on the body is significantly less than the maximum
static capability.
Endurance usually limits dynamic work when loads
are not extreme. Toyota uses this effect by designing workcells that
require considerable walking and movement. This reduces static
work with a slight increase in dynamic work. There are many other
advantages such as allowing work
balance through circulation.
Usually, tasks should not
require operators to exert more than 30 percent of their maximum
muscle force in a prolonged or repetitive way. All muscular
exertions beyond 50 percent of the maximum level should be avoided.
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Ergonomic
Series Articles
Ergonomics
In Lean Manufacturing
Physiology
Biomechanics In Workstation Design
Anthropometry
Man-Machine Allocation
Musculoskeletal Disorders
Principles of Ergonomics
Ergo Download
References
ANSI/HFES100-1988,
Human Factors & Ergonomic Society, 1988.
Barnes,
Ralph M., Motion and Time Study, Second Edition, John Wiley
& Sons, New York, 1940. Eastman
Kodak Company, Ergonomic Design for People at Work, Van
NostrandReinhold, New York, 1986. Fraser,
M., the Worker At Work, Taylor & Francis, New York, 1989. Lee,
Q, Nelson W., Amundsen, A., & Tuttle, H., Facilities
and Workplace Design, Institute of Industrial Engineers,
Atlanta, Georgia, 1996. Woodson,
Wesley E. and Conover, Donald W., Human Engineering for Equipment
Design 2nd Rev. Edition, University of California Press, Berkely,
1966. Zandin,
Kjell B. and Maynard, Harold B., Industrial Engineering Handbook
5TH Edition, McGraw-Hill, New York, 2001. |
