PNF STRETCHING-PRINCIPLES & METHODS OF PROPRIOCEPTIVE NEUROMUSCULAR FACILITATION: One of the most important elements in any fitness program is stretching. Use the body’s proprioception system to improve flexibility and range of motion in your clients. Identify the role of joint and muscle structures as they relate to stretching and learn four different proprioceptive neuromuscular facilitation (PNF) stretching protocols. Authored by: Jeff Larson, RPT, L/ATC