April 7, 2010 by David Fitzgerald

A recent discussion amongst colleagues on the merits of different types of stretching and the clinical applications in which to apply these methods is the topic of today’s discussion.  The fundamental debate revolves around the merits of active versus passive stretching.  As with all these things there are vigorous advocates in each camp with conflicting research which is selectively quoted depending on the perspective.

In the Sports Science arena several studies have indicated in distance runners that routine stretches make little difference to the injury incidence profile and indeed some studies have suggested that athletic performance may be temporarily compromised in the short-term after athletes perform sustained passive stretching.  Theoretical arguments here relate to loosing elasticity and resistance within contractile tissues – the equivalent of overstretching a spring and therefore reducing the energy efficiency during muscle contraction and loading.

Of course the corollary to this is that excessively tight musculo-tendinous structures are more resistant to deformation, require more muscle force to generate elongation and are therefore subject to higher demands upon the system.

So the balance to be struck here is some way of trying to determine what the “optimal” force within the system is to provide efficient biomechanical capacity.  Alternatively, active stretching- sometimes called dynamic / ballistic stretching involves more rapid ballistic kind of movements on the basis that it simulates normal muscle function and simultaneously involves the neural system to maintain and coordinate muscle activity.

However because the movement patterns tend to be more general (global) this increases the potential for compensation in other areas of the movement chain which raises the challenge of how do we ensure that we achieve movement in the target area?

This concept was addressed initially by Shirley Sahrmann in the U.S. with her concept of “relative flexibility” being particularly relevant to this discussion.  In summary her definition of relative flexibility is the process of establishing the proportion of movement which occurs throughout the kinetic chain for a functional movement pattern.  Using this type of operational definition involves integrating aspects of localised muscle control superimposed upon systemic global control in conjunction with the capacity to lengthen and elongate tissues the target area.  This is a particularly useful type of approach because it acts as a unifying strategy to integrate targeted stabilising muscle activity, flexibility in tight areas and sequencing combinations of activities to challenge the system for the specific functional movement under examination.  Using this type of strategy we can develop a functional screening profile which can be very helpful clinically.  Types of Stretching

Just as there are different types of flexibility, there are also different types of stretching. Stretches are either dynamic (meaning they involve motion) or static (meaning they involve no motion). Dynamic stretches affect dynamic flexibility and static stretches affect static flexibility (and dynamic flexibility to some degree).

The different types of stretching are:

1. ballistic stretching
2. dynamic stretching
3. active stretching
4. passive (or relaxed) stretching
5. static stretching
6. isometric stretching
7. PNF stretching

Ballistic Stretching

Ballistic stretching uses the momentum of a moving body or a limb in an attempt to force it beyond its normal range of motion. This is stretching, or “warming up”, by bouncing into (or out of) a stretched position, using the stretched muscles as a spring which pulls you out of the stretched position. (e.g. bouncing down repeatedly to touch your toes.) This type of stretching is not considered useful and can lead to injury. It does not allow your muscles to adjust to, and relax in, the stretched position. It may instead cause them to tighten up by repeatedly activating the stretch reflex (see section

Dynamic Stretching

Dynamic stretching, according to Kurz, “involves moving parts of your body and gradually increasing reach, speed of movement, or both.” Do not confuse dynamic stretching with ballistic stretching! Dynamic stretching consists of controlled leg and arm swings that take you (gently!) to the limits of your range of motion. Ballistic stretches involve trying to force a part of the body beyond its range of motion. In dynamic stretches, there are no bounces or “jerky” movements. An example of dynamic stretching would be slow, controlled leg swings, arm swings, or torso twists.

Dynamic stretching improves dynamic flexibility and is quite useful as part of your warm-up for an active or aerobic workout (such as a dance or martial-arts class). According to Kurz, dynamic stretching exercises should be performed in sets of 8-12 repetitions:

Perform your exercises (leg raises, arm swings) in sets of eight to twelve repetitions. If after a few sets you feel tired — stop. Tired muscles are less elastic, which causes a decrease in the amplitude of your movements. Do only the number of repetitions that you can do without decreasing your range of motion. More repetitions will only set the nervous regulation of the muscles’ length at the level of these less than best repetitions and may cause you to lose some of your flexibility. What you repeat more times or with a greater effort will leave a deeper trace in your [kinesthetic] memory! After reaching the maximal range of motion in a joint in any direction of movement, you should not do many more repetitions of this movement in a given workout. Even if you can maintain a maximal range of motion over many repetitions, you will set an unnecessarily solid memory of the range of these movements. You will then have to overcome these memories in order to make further progress.

Active Stretching

Active stretching is also referred to as static-active stretching. An active stretch is one where you assume a position and then hold it there with no assistance other than using the strength of your agonist muscles. For example, bringing your leg up high and then holding it there without anything (other than your leg muscles themselves) to keep the leg in that extended position. The tension of the agonists in an active stretch helps to relax the muscles being stretched (the antagonists) by reciprocal inhibition.

Active stretching increases active flexibility and strengthens the agonistic muscles. Active stretches are usually quite difficult to hold and maintain for more than 10 seconds and rarely need to be held any longer than 15 seconds.

Many of the movements (or stretches) found in various forms of yoga are active stretches.

Passive Stretching

Passive stretching is also referred to as relaxed stretching, and as static-passive stretching. A passive stretch is one where you assume a position and hold it with some other part of your body, or with the assistance of a partner or some other apparatus. For example, bringing your leg up high and then holding it there with your hand. The splits is an example of a passive stretch (in this case the floor is the “apparatus” that you use to maintain your extended position).

Slow, relaxed stretching is useful in relieving spasms in muscles that are healing after an injury. Obviously, you should check with your doctor first to see if it is okay to attempt to stretch the injured muscles .

Relaxed stretching is also very good for “cooling down” after a workout and helps reduce post-workout muscle fatigue, and soreness..

Static Stretching

Many people use the term “passive stretching” and “static stretching” interchangeably. However, there are a number of people who make a distinction between the two. According to M. Alter:

Static stretching involves holding a position. That is, you stretch to the farthest point and hold the stretch .

Passive stretching is a technique in which you are relaxed and make no contribution to the range of motion. Instead, an external force is created by an outside agent, either manually or mechanically.

Notice that the definition of passive stretching given in the previous section encompasses both of the above definitions. Throughout this document, when the term static stretching or passive stretching is used, its intended meaning is the definition of passive stretching as described in the previous section. You should be aware of these alternative meanings, however, when looking at other references on stretching.

Isometric Stretching

Isometric stretching is a type of static stretching (meaning it does not use motion) which involves the resistance of muscle groups through isometric contractions (tensing) of the stretched muscles The use of isometric stretching is one of the fastest ways to develop increased static-passive flexibility and is much more effective than either passive stretching or active stretching alone. Isometric stretches also help to develop strength in the “tensed” muscles (which helps to develop static-active flexibility), and seems to decrease the amount of pain usually associated with stretching.

The most common ways to provide the needed resistance for an isometric stretch are to apply resistance manually to one’s own limbs, to have a partner apply the resistance, or to use an apparatus such as a wall (or the floor) to provide resistance.

An example of manual resistance would be holding onto the ball of your foot to keep it from flexing while you are using the muscles of your calf to try and straighten your instep so that the toes are pointed.

An example of using a partner to provide resistance would be having a partner hold your leg up high (and keep it there) while you attempt to force your leg back down to the ground.

An example of using the wall to provide resistance would be the well known “push-the-wall” calf-stretch where you are actively attempting to move the wall (even though you know you can’t).

Isometric stretching is not recommended for children and adolescents whose bones are still growing. These people are usually already flexible enough that the strong stretches produced by the isometric contraction have a much higher risk of damaging tendons and connective tissue. Kurz strongly recommends preceding any isometric stretch of a muscle with dynamic strength training for the muscle to be stretched. A full session of isometric stretching makes a lot of demands on the muscles being stretched and should not be performed more than once per day for a given group of muscles (ideally, no more than once every 36 hours).

The proper way to perform an isometric stretch is as follows:

1. Assume the position of a passive stretch for the desired muscle.
2. Next, tense the stretched muscle for 7-15 seconds (resisting against some force that will not move, like the floor or a partner).
3. Finally, relax the muscle for at least 20 seconds.

Some people seem to recommend holding the isometric contraction for longer than 15 seconds, but according to SynerStretch (the videotape), research has shown that this is not necessary. So you might as well make your stretching routine less time consuming.

How Isometric Stretching Works

Recall from our previous discussion that there is no such thing as a partially contracted muscle fiber: when a muscle is contracted, some of the fibers contract and some remain at rest (more fibers are recruited as the load on the muscle increases). Similarly, when a muscle is stretched, some of the fibers are elongated and some remain at rest During an isometric contraction, some of the resting fibers are being pulled upon from both ends by the muscles that are contracting. The result is that some of those resting fibers stretch!

Normally, the handful of fibers that stretch during an isometric contraction are not very significant. The true effectiveness of the isometric contraction occurs when a muscle that is already in a stretched position is subjected to an isometric contraction. In this case, some of the muscle fibers are already stretched before the contraction, and, if held long enough, the initial passive stretch overcomes the stretch reflex and triggers the lengthening reaction inhibiting the stretched fibers from contracting. At this point, according to SynerStretch:

When you isometrically contracted, some of the resting fibers would contract, many of the resting fibers would stretch, and many of the already stretched fibers, which are being prevented from contracting by the inverse myotatic reflex [the lengthening reaction], would stretch even more. When the isometric contraction was relaxed and the contracting fibers returned to their resting length, the stretched fibers would retain their ability to stretch beyond their normal limit. … the whole muscle would be able to stretch beyond its initial maximum, and you would have increased flexibility …

The reason that the stretched fibers develop and retain the ability to stretch beyond their normal limit during an isometric stretch has to do with the muscle spindles: The signal which tells the muscle to contract voluntarily, also tells the muscle spindle’s (intrafusal) muscle fibers to shorten, increasing sensitivity of the stretch reflex. This mechanism normally maintains the sensitivity of the muscle spindle as the muscle shortens during contraction. This allows the muscle spindles to habituate (become accustomed) to an even further-lengthened position.

PNF Stretching

PNF stretching is currently the fastest and most effective way known to increase static-passive flexibility. PNF is an acronym for proprioceptive neuromuscular facilitation. It is not really a type of stretching but is a technique of combining passive stretching  and isometric stretching in order to achieve maximum static flexibility. Actually, the term PNF stretching is itself a misnomer. PNF was initially developed as a method of rehabilitating stroke victims. PNF refers to any of several post-isometric relaxation stretching techniques in which a muscle group is passively stretched, then contracts isometrically against resistance while in the stretched position, and then is passively stretched again through the resulting increased range of motion. PNF stretching usually employs the use of a partner to provide resistance against the isometric contraction and then later to passively take the joint through its increased range of motion. It may be performed, however, without a partner, although it is usually more effective with a partner’s assistance.

Most PNF stretching techniques employ isometric agonist contraction/relaxation where the stretched muscles are contracted isometrically and then relaxed. Some PNF techniques also employ isometric antagonist contraction where the antagonists of the stretched muscles are contracted. In all cases, it is important to note that the stretched muscle should be rested (and relaxed) for at least 20 seconds before performing another PNF technique. The most common PNF stretching techniques are:

the hold-relax

This technique is also called the contract-relax. After assuming an initial passive stretch, the muscle being stretched is isometrically contracted for 7-15 seconds, after which the muscle is briefly relaxed for 2-3 seconds, and then immediately subjected to a passive stretch which stretches the muscle even further than the initial passive stretch. This final passive stretch is held for 10-15 seconds. The muscle is then relaxed for 20 seconds before performing another PNF technique.

the hold-relax-contract

This technique is also called the contract-relax-contract, and the contract-relax-antagonist-contract (or CRAC). It involves performing two isometric contractions: first of the agonists, then, of the antagonists. The first part is similar to the hold-relax where, after assuming an initial passive stretch, the stretched muscle is isometrically contracted for 7-15 seconds. Then the muscle is relaxed while its antagonist immediately performs an isometric contraction that is held for 7-15 seconds. The muscles are then relaxed for 20 seconds before performing another PNF technique.

the hold-relax-swing

This technique (and a similar technique called the hold-relax-bounce) actually involves the use of dynamic or ballistic stretches in conjunction with static and isometric stretches. It is very risky, and is successfully used only by the most advanced of athletes and dancers that have managed to achieve a high level of control over their muscle stretch reflex It is similar to the hold-relax technique except that a dynamic or ballistic stretch is employed in place of the final passive stretch.

Notice that in the hold-relax-contract, there is no final passive stretch. It is replaced by the antagonist-contraction which, via reciprocal inhibition, serves to relax and further stretch the muscle that was subjected to the initial passive stretch. Because there is no final passive stretch, this PNF technique is considered one of the safest PNF techniques to perform (it is less likely to result in torn muscle tissue). Some people like to make the technique even more intense by adding the final passive stretch after the second isometric contraction. Although this can result in greater flexibility gains, it also increases the likelihood of injury.

Even more risky are dynamic and ballistic PNF stretching techniques like the hold-relax-swing, and the hold-relax-bounce. If you are not a professional athlete or dancer, you probably have no business attempting either of these techniques (the likelihood of injury is just too great). Even professionals should not attempt these techniques without the guidance of a professional coach or training advisor. These two techniques have the greatest potential for rapid flexibility gains, but only when performed by people who have a sufficiently high level of control of the stretch reflex in the muscles that are being stretched.

Like isometric stretching PNF stretching is also not recommended for children and people whose bones are still growing (for the same reasons. Also like isometric stretching, PNF stretching helps strengthen the muscles that are contracted and therefore is good for increasing active flexibility as well as passive flexibility. Furthermore, as with isometric stretching, PNF stretching is very strenuous and should be performed for a given muscle group no more than once per day (ideally, no more than once per 36 hour period).

The initial recommended procedure for PNF stretching is to perform the desired PNF technique 3-5 times for a given muscle group (resting 20 seconds between each repetition). However, HFLTA cites a 1987 study whose results suggest that performing 3-5 repetitions of a PNF technique for a given muscle group is not necessarily any more effective than performing the technique only once. As a result, in order to decrease the amount of time taken up by your stretching routine (without decreasing its effectiveness), HFLTA recommends performing only one PNF technique per muscle group stretched in a given stretching session.

How PNF Stretching Works

Remember that during an isometric stretch, when the muscle performing the isometric contraction is relaxed, it retains its ability to stretch beyond its initial maximum length . Well, PNF tries to take immediate advantage of this increased range of motion by immediately subjecting the contracted muscle to a passive stretch.

The isometric contraction of the stretched muscle accomplishes several things:

1. As explained previously it helps to train the stretch receptors of the muscle spindle to immediately accommodate a greater muscle length.
2. The intense muscle contraction, and the fact that it is maintained for a period of time, serves to fatigue many of the fast-twitch fibers of the contracting muscles This makes it harder for the fatigued muscle fibers to contract in resistance to a subsequent
3. The tension generated by the contraction activates the golgi tendon organ, which inhibits contraction of the muscle via the lengthening reaction. Voluntary contraction during a stretch increases tension on the muscle, activating the golgi tendon organs more than the stretch alone. So, when the voluntary contraction is stopped, the muscle is even more inhibited from contracting against a subsequent stretch.

PNF stretching techniques take advantage of the sudden “vulnerability” of the muscle and its increased range of motion by using the period of time immediately following the isometric contraction to train the stretch receptors to get used to this new, increased, range of muscle length. This is what the final passive (or in some cases, dynamic) stretch accomplishes.

Enjoy the clinical challenge
David