Flexibility refers to the range of motion of the body and its joints without strain. There are two types of flexibility: active flexibility which is self-produced motion and passive flexibility which uses external forces. Flexibility affects other performance factors and is necessary for development of movement skills, prevention of injuries, and motor learning. Factors that influence flexibility include joint structure, muscles, coordination, strength, age, gender, activity level, and weight training technique. The document discusses static and dynamic stretching techniques. It concludes that improving flexibility in the ankles, hips, and trunk can increase speed and save energy during athletic performance.