Which of these is a primary function of flexibility training?

The primary function of flexibility training is to promote a greater range of motion. Flexibility training typically involves exercises that stretch the muscles, tendons, and ligaments, allowing for increased mobility in the joints. This enhanced range of motion can improve performance in physical activities, reduce the risk of injury, and aid in recovery after workouts.

While building muscle mass and improving bone density are related to strength training and weight-bearing exercises respectively, they do not directly relate to flexibility training's primary goal. Increasing endurance focuses on the ability to sustain physical activity over time, which is not the main aim of flexibility exercises either. Thus, promoting a greater range of motion is distinctly the core purpose of flexibility training.