PNF stands for Proprioceptive Neuromuscular Facilitation, which is an advanced form of flexibility training that involves both stretching and contracting of the muscle group being targeted. PNF stretching is one of the most effective forms of stretching for improving flexibility and increasing range of motion. It was initially developed by physiotherapists as a method of rehabilitating stroke victims and later expanded to treating musculoskeletal conditions. PNF stretching can be used to improve muscle elasticity and has been shown to have a positive effect on active and passive range of motion. It can also be used by athletes to improve their performance. PNF stretching requires the help of a partner or an inanimate object, and it involves alternating between a static stretch-and-hold and an isometric contraction of the muscle being stretched. PNF stretching can be risky if not done properly, so it is recommended to receive professional assistance.