Which of the following is true about isometric training?

Isometric training is characterized by static muscle contractions where the muscle exerts force without changing its length. This form of training involves voluntarily contracting a muscle while keeping the joint angle and muscle length unchanged, allowing for the development of strength at specific points in the muscle's range of motion. It is often performed against an immovable object or during holds in various positions.

The other choices present alternative forms of exercise: lengthening muscles through movement pertains to dynamic or concentric/eccentric training, dynamic movements relate to exercises that involve movement through a range of motion and are typically associated with endurance or aerobic workout routines, and aerobic exercise primarily emphasizes cardiovascular health rather than muscle strength. Thus, understanding isometric training's focus on static muscle contractions clarifies why it stands out among the options provided.