Final answer:
Static stretching is the most common type of flexibility training that involves slow and constant motion held in the final position, at a point of mild discomfort for 15 to 30 seconds.
Step-by-step explanation:
The most common type of flexibility training that involves slow and constant motion held in the final position is Static stretching. This type of stretching is performed by slowly moving into the desired position, then holding it for 15 to 30 seconds, at a point of mild discomfort. Static stretching helps improve flexibility and joint range of motion and is commonly used before and after exercise.