Static stretching is the type of stretching where you take a muscle to its outer range, until you can feel a gentle stretch in the muscle belly, and hold it at that point. Stretches are usually held for between 20 and 60 seconds and should be pain-free.
Static stretches work because as you hold the position, with the muscle under tension, a stretch reflex causes muscle relaxation. When this occurs the muscle can be stretched a little further, without pain or discomfort. If there are feelings of pain or discomfort then the stretch should be reduced to prevent over-stretching and muscle damage.
Static stretching is the most commonly performed type of stretching, partly due to it being the safest method of stretching due to the relatively low levels of tension developed.
Static stretches can be either active or passive. Active stretches involve the athlete moving the joint through its range of motion and holding it at the point of stretch themselves. Passive stretching is sometimes also known as partner stretching and involves a partner moving the joint to the point of tension in the muscle and holding it for the athlete, whilst they relax! If using this type of stretching, communication is important to ensure the partner is aware of any discomfort in the muscle and eases off accordingly.
Dynamic stretching is sometimes also known as active stretching and is now being seen as a replacement for static stretching during a warm-up as it replicates the kind of movements which are common in most sports, and can be adapted to suit the sport and individual. Dynamic stretches involve taking a muscle through its entire range of motion, starting with a small movement and gradually increasing both movement range and speed. Examples of these types of drills include high knees, cariocas and lunges.
In a warm-up, dynamic stretches are usually performed following an initial period of CV exercise (jogging/cycling etc) and usually include a minimum of 5 of this type of drill, each performed 6-8 times at slow, medium and fast speeds. All movements should be under complete control.
PNF stands for Proprioceptive Neuromuscular Facilitation and can take on several forms including hold-relax; contract-relax; and rhythmic initiation. PNF started to become popular in the 1960's and has since become a common treatment for many physiotherapists and other sports injury professionals.
PNF can be either completely passive (meaning the therapist moves the limb through its ranges of motion) or active assisted, in which the athlete plays a role in the treatment. In this case it requires an isometric contraction before the stretch. So for example, to a use hold-relax PNF technique on the hamstrings, the athlete would lay on the back and raise the straight leg up off the bed (contracting the hip flexors Rectus Femoris and Iliopsoas) to the starting position. From here, the therapist or partner provides resistance as the athlete isometrically contracts the hamstrings (as if trying to push the foot back down to the floor) for a minimum of 6 seconds. Following this the athlete contracts the hip flexors again to raise the leg higher and further stretch the hamstrings
This works on the theories of reciprocal inhibition (or innervation) and post-isometric relaxation. Reciprocal inhibition is based on a reflex loop, controlled by the muscle spindles. When an agonist muscle contracts (for example the quads, causing knee extension), the antagonist muscle is inhibited, causing it to relax (in this example the hamstrings), allowing the full movement of the antagonist muscle (knee extension). Post-isometric relaxation is thought to be controlled by the golgi tendon organs, sensors within the muscle which are sensitive to muscle tension. When a muscle is contracted isometrically for a period of time, this results in an inhibition of the muscle, resulting in relaxation.
PNF can also be used for treatments other than stretching, for example muscle strengthening in a rehabilitation setting. PNF in this sense involves spiral-diagonal movements, as are used in most daily and sporting activities. Very few activities use only one plane of movement, there is usually an combination of two or all three planes (flexion/extension; adduction/abduction; and rotation). For this reason, PNF incorporates these spiral-diagonal movements to help train the body in the way in which it is most often used.