The stomach is a muscular sac that is important for absorbing food and preparing food for further digestion.
An isotonic exercise is one in which the tension applied to muscle remains unchanged while the length of opposing muscles changes. Lifting weights is a good example of an isotonic exercise. Contractions that occur during isotonic exercises are classified as either concentric or eccentric. In a concentric contraction the muscular force overcomes the resistance whereas in an eccentric contraction the resistance is too great to be overcome by muscular force. This leads to a lengthening of the muscle being subjected to the load. An example of an eccentric contraction would be trying to do bicep curls with a weight that is too heavy to get off the ground. Almost all bodybuilding exercises done with weights execute isotonic movements, primarily of the concentric kind.