Friday, April 13, 2012

Human Effort - Nature and Effects

Biomechanics of Motion
Biomechanics deals with the various aspects of physical movements of the body and body members. The physical structure of the body (the skeleton), the skeletal muscles, the nervous system, and the metabolic processes are involved in movements made by  a person.
The Skeletal Structure
206 bones form the skeleton. Certain bone structures like skull and ribs protect the essential organs of the humans. Some bone structures execute physical activities. Two general types of joints are principally used in physical activities, synovial joints and cartilaginous joints. The synovial joints include hinge joints, pivot joints, and ball-and-socket joint. Cartilaginous joint are those of the vertebrae of the spine and they help in forward bending of the body. They also permit rotation. The bones of the body are held together at their joints by ligaments.
The Skeletal Muscles
The skeletal muscles convert chemical energy into mechanical energy or work. The ends of muscles blend into tendons which are connected to skeletal bones. When muscles are activated they apply forces on bones.
Control of Muscles
Control of muscles is achieved though nerves. There are sensory nerves and motor nerves in muscles. Motor nerves are responsible for the movements of muscles.
Movements of Body Members
Kinesiology is the name given to study of human movements as a function of the construction of musculoskeletal system.
Movement Types
Flexion: bending
Extension: straightening
Adduction: moving toward the centre of the body
Abduction: Moving away from the centre of the body
Medial rotation: turning toward the midline of the body
lateral rotation: turning away from the midline of the body
Pronation: (in case of arms) rotating the forearm such that palm faces downwards
Supination (In case of arms) rotating the forearm such the palm faces upwards
Bounds for Energy Expenditure of an Operator
Lehmann (1958) estimated that a normal man can give a maximum energy output of 4800 kcal/day in the long run. If 2300 kcal is kept for basal metabolism and leisure activities, 2500 kcal can be spent in productive work or career related work. He advocated using 2000 kcal a normal load and this comes to around 4.2 kcal/min.
Body Dimensions
Body dimensions have to be considered in designing hand tools and control devices that are used by operators. The systematic study of individual differences in size was started by Belgian astronomer Quetelet who published his Anthropometrie in 1870.
Static and functional measurments of operators/representative human population are being taken to use in human effort engineering. Static measurements are taken wehn an individual is in nonmoving position. Functional mesurements are taken with people assuming common working positions.
Strength of a Person
Bailey, Robert W., Human Performance Engineering: A Guide to System Designers, Prentice Hall, New Jersey, 1982.
Chaffin, D.B., Some Effects of Physical Exertion, Western Electric/Univerisity of Michigan Research Report, 1972.
Tichauer, E.R., The Biomechanical Basis of Ergonomics, Wiley, New York, 1978.
Original knol - 1797

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