PNF is a form of stretching designed to increase the flexibility of muscles and increase the range of movement. PNF is a progressive stretch involving muscle contraction and relaxation. Your physiotherapist will gently stretch the muscle and you will resist the stretch by contracting the muscle for about 5 seconds. Your therapist will indicate the force of contraction required and this depends on the condition of the muscle. You then relax the muscle and your physiotherapist will gently stretch the muscle further for about 30 seconds. There are then about 30 seconds of rest and the process is repeated several times.