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James A Ashton-miller
05-14-1995, 12:10 PM
When the load on a muscle exceeds its contractile force, is the resultant
lengthening process or state most accurately called a 'pliometric',
an'excentric', an 'eccentric' or a 'lengthening' process, state (or
"contraction")?

A trip to the dictionaries on my bookshelf revealed:
ex: from the Latin meaning 'out of, from'
ec: a variant of 'ex'
-centric: from the Greek 'kentron' meaning 'pertaining to the center'
eccentric: from the Greek 'ekkentros' meaning 'out of center'
plio-: from the Greek 'pleion' meaning 'more'
metric: from the Greek 'metron' meaning 'pertaining to distance'
con: from the Latin 'com' meaning 'with, together'
contrahere: from the Latin meaning 'to draw together, reduce in size'
mio-: from the Greek meaning 'less'

On lengthening muscle:
The term 'excentric' has been ascribed to Asmussen, E. (1953) Acta
Physiol. Scand. 28:365-82. This seems slightly superior to 'eccentric'
which has meant 'deviating from a circular path' for several thousand
years. The term 'pliometric' is widely used to describe a form of muscle
training involving setting up 'lengthening contractions'.
Because each muscle (and, indeed, sarcomere) has a 'kentron',
'excentric' does not appear an unreasonable term, given the above
definitions. On the other hand, the use of 'pliometric' neatly
circumvents the need to define a 'kentron' at all; it simply refers to
'more' distance between the ends of the muscle.
As an aside, it seems more accurate to use words 'state' or 'process'
rather than 'contraction' in conjunction with 'excentric' or
'pliometric', because the term 'lengthening contraction' contains words
that are antonymic.

On a shortening muscle contraction:
Similarly, is it preferable to use 'miometric contraction' rather than
'concentric contraction'?

Is it perhaps time to standardize these terms? Has any field
(biomechanics, muscle physiology, kinesiology, orthopaedics and physical
medicine taken the lead in this regard?

James A. Ashton-Miller, Ph.D. -- jaam@umich.edu
Biomechanics Research Laboratories
Dept. Mech. Eng'ng & Appl. Mech., and
Institute of Gerontology,
University of Michigan, Ann Arbor, MI 48109-2125