The American Heritage® Dictionary of the English Language, 4th Edition
n. Exercise or a system of exercises in which isometric muscular contraction is used to strengthen and tone muscles, performed by the exertion of effort against resistance, usually of a stationary object.
the GNU version of the Collaborative International Dictionary of English
n. Same as isometric exercise.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. muscle-building exercises (or a system of musclebuilding exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change)
Word Usage
"Although situps can be an effective stomach exercise, I firmly believe that doing stomach isometrics is much more effective."