Stretching can take various different forms. Static stretching is the most common. PNF stretching, muscle energy techniques, ballistic stretching and neural stretching are other types.
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.
Muscle Energy Techniques
Muscle Energy techniques (or MET's) are another form of active-assisted stretches, similar to PNF, and developed around the same time, in the world of Osteopathy. Like PNF, MET's use an isometric contraction of the agonist prior to stretching. The difference is in the force of the isometric contraction, which in MET's are a lot lower. An MET stretch is performed in the following way, using the hamstrings as an example:
The therapist moves the hip into flexion, with the athlete on their back, until they encounter the point of resistance - where the movement stiffens, due to tightness in the hamstrings. They hold this position for 15-20 seconds. They then ease off slightly from the stretch and ask the athlete to try to push the leg back down to the couch, which causes an isometric contraction of the hamstrings. In MET's, this contraction should be a maximum of 20% of the athletes total strength. This contraction is held for around 10 seconds, before the therapist asks them to relax and pushes the limb further, increasing the stretch, until resistance is felt once more. The process is usually repeated 3-5 times for each muscle.
Ballistic stretching is the bouncing type of stretching, where you take the muscle to near its limit and then bounce to stretch it further. For example reaching over to touch your toes and bouncing to increase the range. This type of stretching is rarely recommended due to the injury possibilities and no beneficial effect over other, safer, forms of stretching such as PNF and dynamic stretches.
Neural stretching refers to stretching the structures of the nervous system. This is necessary in injuries where there is excess neural tension or restriction of movement of neural structures, commonly around the neck and shoulder girdle, or pelvis area. Neural stretches are adaptations of neural tension tests, such as the slump test and the upper limb tension test. The limb is taken to the point of stretch and held for a maximum of 10 seconds, although initially this may be as little as 3-4 seconds to avoid causing damage to the nerves. This kind of stretching should only be performed under the supervision of a qualified therapist.