Walker, Brad. Ultimate Guide to Stretching & Flexibility. 3rd ed. 2011. Print.
Stretching is slightly more technical than swinging a leg over a park bench. There are methods and techniques that will maximize the benefits and minimize the risk of injury. In this chapter we will look at the different types of stretching, the particular benefits, risks and uses, plus a description of how each type is performed.
Just as there are many different ways to strength train, there are also many different ways to stretch. However, it is important to note that although there are many different ways to stretch, no one way, or no one type of stretching is better than another. Each type has its own advantages and disadvantages, and the key to getting the most out of stretching lies in being able to match the right type of stretching to the purpose, or goal trying to be achieved.
For example; PNF and passive stretching are great for creating permanent improvements in flexibility, but they are not very useful for warming up or preparing the body for activity. Dynamic stretching, on the other hand, is great for warming up but can be dangerous if used in the initial stages of injury rehabilitation.
Although there are many different ways to stretch, they can all be grouped into one of two categories; static or dynamic.
Static Stretches
The term static stretches refers to stretching exercises that are performed without movement. In other words, the individual gets into the stretch position and holds the stretch for a specific amount of time. Listed below are five different types of static stretching exercises.
Static Stretching
Static stretching is performed by placing the body into a position whereby the muscle (or group of muscles) to be stretched is under tension. Both the antagonist, or opposing muscle group and the agonist, or muscles to be stretched are relaxed. Then slowly and cautiously the body is moved to increase the tension on the stretched muscle (or group of muscles). At this point the position is held or maintained to allow the muscles to relax and lengthen.
The stretch to the right is a classic example of a static stretch in which the opposing muscles and the hamstring and back muscles are relaxed.
A minimum hold time of about 20 seconds is required for the muscles to relax and start to lengthen, while diminishing returns are experienced after 45 to 60 seconds.
Static stretching is a very safe and effective form of stretching with a limited threat of injury. It is a good choice for beginners and sedentary individuals.
Passive (or Assisted) Stretching
This form of stretching is very similar to static stretching; however another person or apparatus is used to help further stretch the muscles. Due to the greater force applied to the muscles, this form of stretching can be slightly more hazardous. Therefore it is very important that any apparatus used is both solid and stable. When using a partner it is imperative that no jerky or bouncing force is applied to the stretched muscles. So, choose a partner carefully; the partner is responsible for the safety of the muscles and joints while you are performing the stretching exercises.
The stretch on the left is an example of a passive stretch in which a partner is used to stretch the chest and shoulder muscles. 
Passive stretching is useful in helping to attain a greater range of motion, but carries with it a slightly higher risk of injury. It can also be used effectively as part of a rehabilitation program or as part of a cool-down.
Active Stretching
Active stretching is performed without any aid or assistance from an external force. This form of stretching involves using only the strength of the opposing muscles helps to relax the stretched muscles.
A classic example of an active stretch is one where an individual raises one leg straight out in front, as high as possible, and then maintains that fixed position without any assistance from a partner or object. 
Active stretching is useful as a rehabilitation tool and very effective as a form of conditioning before moving onto dynamic stretches. This type of stretching exercise is usually quite difficult to hold and maintain for long periods of time and therefore the stretch position is usually only held for 10 to 15 seconds.
PNF Stretching
PNF stretching ( Proprioceptive Neuromuscular Facilitation ), sometimes referred to as Facilitated Stretching , is a more advanced form of flexibility training that involves both the stretching and contracting of the muscle group being targeted. PNF stretching was originally developed as a form of rehabilitation and for that function it is very effective. It is also excellent for targeting specific muscle groups, and as well as increasing flexibility, it also improves muscular strength.
There are many different variations of the PNF stretching principle and sometimes it is referred to as Contract-Relax stretching or Hold-Relax stretching. Post Isometric Relaxation (PIR) is another variation of the PNF technique.
To perform a PNF stretch, the area to be stretched is positioned so that the muscle (or group of muscles) is under tension. The individual then contracts the stretched muscle group for 5 to 6 seconds while a partner (or immovable object) applies sufficient resistance to inhibit movement. The force of contraction should be relative to the level of conditioning. The contracted muscle group is then relaxed and a controlled stretch is immediately applied for about 30 seconds. The athlete is then allowed 30 seconds to recover and the process is repeated 2 to 4 times.
Information differs slightly about timing recommendations for PNF stretching. Although there are conflicting responses to the questions; for how long should I contract the muscle group and for how long should I rest between each stretch , it is my professional opinion, that through a study of research literature and personal experience, the previous timing recommendations provide the maximum benefits from PNF stretching.
Isometric Stretching
Isometric stretching is a form of passive stretching similar to PNF stretching, but the contractions are held for a longer period of time. Isometric stretching places high demands on the stretched muscles and is not recommended for children or adolescents who are still growing. Other recommendations include allowing at least 48 hours rest between isometric stretching sessions and performing only one isometric stretching exercise per muscle group in a session.
A classic example of how isometric stretching is used is the Leaning Heel-back Calf Stretch to the right. In this stretch the participant stands upright, leans forward towards a wall and then places one foot as far from the wall as is comfortable while making sure that the heel remains on the ground. In this position, the participant contracts the calf muscles as if trying to raise the heel off the ground.
To perform an isometric stretch; assume the position of the passive stretch and then contract the stretched muscle for 10 to 15 seconds. Be sure that all movement of the limb is prevented. Then relax the muscle for at least 20 seconds. This procedure should be repeated 2 to 5 times.
Dynamic Stretches
The term dynamic stretches refers to stretching exercises that are performed with movement. In other words, the individual uses a swinging or bouncing movement to extend their range of motion and flexibility. Listed below are four different types of dynamic stretching exercises.
Ballistic Stretching
Ballistic stretching is an outdated form of stretching that uses momentum generated by rapid swinging, bouncing and rebounding movements to force a body part past its normal range of motion.
The risks associated with ballistic stretching far outweigh the gains, especially when greater gains can be achieved by using other forms of stretching like dynamic stretching and PNF stretching. Other than potential injury, the main disadvantage of ballistic stretching is that it fails to allow the stretched muscle time to adapt to the stretched position and instead may cause the muscle to tighten up by repeatedly triggering the stretch reflex.
Dynamic Stretching
Unlike ballistic stretching, dynamic stretching uses a controlled, soft bounce or swinging movement to move a particular body part to the limit of its range of motion. The force of the bounce or swing is gradually increased but should never become radical or uncontrolled.
Do not confuse dynamic stretching with ballistic stretching. Dynamic stretching is slow, gentle and very purposeful. At no time during dynamic stretching should a body part be forced past the joints normal range of motion. Ballistic stretching, on the other hand, is much more aggressive and its very purpose is to force the body part beyond the limit of its normal range of motion.
Active Isolated Stretching
Active isolated (AI) stretching is a form of stretching developed by Aaron L. Mattes, and is sometimes referred to as The Mattes Method . It works by contracting the antagonist, or opposing muscle group, which forces the stretched muscle group to relax. The procedure for performing an AI stretch is as follows.
1. Choose the muscle group to be stretched and then get into a position to begin the stretch.
2. Actively contract the antagonist, or opposing muscle group.
3. Move into the stretch quickly and smoothly.
4. Hold for 1 to 2 seconds and then release the stretch.
5. Repeat 5 to 10 times.
While AI stretching certainly has some benefits (mainly for the professional or well conditioned athlete), it also has a number of unsubstantiated claims. One such claim is that AI stretching does not engage the stretch reflex (or myotatic reflex) because the stretch is only held for 2 seconds or less. 1,2 This however, defies basic muscle physiology. The stretch reflex in the calf muscle for example is triggered within 3 hundredths of a second, so any claim that AI stretching can somehow bypass or outsmart the stretch reflex is nothing more than wishful thinking.
Resistance Stretching and Loaded Stretching
Resistance stretching and loaded stretching are a form of dynamic stretching that both contract and lengthen a muscle at the same time. They work by stretching a muscle group through its entire range of motion while under contraction. For this reason, both resistance stretching and loaded stretching are as much about strengthening a muscle group as they are about stretching it.
Like AI stretching above, resistance stretching and loaded stretching do have their benefits. Five time Olympic swimmer, Dara Torres credits a portion of her swimming success to the use of resistance stretching. However, these forms of stretching place high demands on the musculo- skeletal system and are therefore only recommended for professional or well conditioned athletes.