There are four main types of flexibility training: dynamic, static, ballistic, and proprioceptive neuromuscular facilitation (PNF). Dynamic stretching uses controlled movement to stretch muscles and is well-suited for sports like dancing. Static stretching slowly stretches muscles to the point of discomfort and holds for 10-30 seconds. Ballistic stretching uses bouncing motions and can cause injury if done incorrectly. PNF stretching combines passive stretching with isometric contractions and is usually done with a partner. Regular flexibility training 2-5 days per week can improve flexibility within a few weeks.