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deviating from the recognized or customary character, practice, etc.; irregular; erratic; peculiar; odd: eccentric conduct; an eccentric person. 2. Geometry. not having the same center; not concentric: used especially of two circles or spheres at least one of which contains the centers of both. 3. (of an axis, axle, etc.) not situated in the center.
In short, it can be said that both concentric and eccentric type of muscle contraction is tried and practiced by the weight lifter during his workouts at the gym during body building exercises. Hence, both these terms are associated with body building and weight lifting. If the muscle lengthens under contraction it amounts to eccentric contraction. Hence, eccentric contraction is exactly the opposite of concentric contraction.