Final answer:
An isometric contraction occurs when a muscle cell generates tension without shortening, such as when trying to lift a weight that is too heavy to move.
Step-by-step explanation:
When a muscle cell generates tension but does not shorten, an isometric contraction occurs. During isometric contractions, the sarcomeres in the muscle may shorten slightly, increasing muscle tension, but the overall length of the muscle does not change. This often happens when a muscle exerts force against an immovable object, where the force produced is not sufficient to overcome the resistance. Isometric contractions are essential in everyday life for tasks such as maintaining posture and joint stability. An example of this type of contraction is trying to lift an immovable heavy weight, where the muscle activates but the elbow joint angle remains unchanged.