PNF Stretching (Proprioceptive Neuro-Muscular Facilitation) is one of the most effective forms of flexibility training. Using isometrics contraction followed by passive stretching, the muscles lengthen, noticeably improving range of motion and flexibility. Applying isometric stretching/PNF to neck and jaw often relieves TMJ and whiplash conditions. PNF mouth work combined with CST can also help some speech issues.