********************************************* STRETCHING AND FLEXIBILITY: Everything you never wanted to know (Part 2 of 4) ********************************************* by Brad Appleton Version: 1.27, Last Modified 95/05/19 Copyright (C) 1993, 1994, 1995 by Bradford D. Appleton Permission is granted to make and distribute verbatim copies of this document provided the copyright notice and this permission notice are preserved on all copies. This document is available in ascii, texinfo, postscript, dvi, and html formats via anonymous ftp from the host `cs.huji.ac.il'. Look under the directory `/pub/doc/faq/rec/martial.arts'. The file name matches the wildcard pattern `stretching.*'. The file suffix indicates the format. For WWW users, the URL is: http://www.cs.huji.ac.il/papers/rma/stretching_toc.html. ------------------------------ Subject: Table of Contents for PART 2 All section titles in this document begin with the prefix "Subject: ". If you wish, you may scan ahead to a particular section by searching for the regular expression /^Subject: SECTION-NAME/. For example, to go to the unnumbered section named "Introduction", you could scan for /^Subject: Intro/; to go to section 1.1, you could scan for /^Subject: 1\.1/; and to go to appendix A, you could scan for /^Subject: Appendix A/. 2 - Flexibility 2.1 - Types of Flexibility 2.2 - Factors Limiting Flexibility 2.2.1 - How Connective Tissue Affects Flexibility 2.2.2 - How Aging Affects Flexibility 2.3 - Strength and Flexibility 2.3.1 - Why Bodybuilders Should Stretch 2.3.2 - Why Contortionists Should Strengthen 2.4 - Overflexibility 3 - Types of Stretching 3.1 - Ballistic Stretching 3.2 - Dynamic Stretching 3.3 - Active Stretching 3.4 - Passive Stretching 3.5 - Static Stretching 3.6 - Isometric Stretching 3.6.1 - How Isometric Stretching Works 3.7 - PNF Stretching 3.7.1 - How PNF Stretching Works ------------------------------ Subject: 2 - Flexibility Flexibility is defined by Gummerson as "the absolute range of movement in a joint or series of joints that is attainable in a momentary effort with the help of a partner or a piece of equipment." This definition tells us that flexibility is not something general but is specific to a particular joint or set of joints. In other words, it is a myth that some people are innately flexible throughout their entire body. Being flexible in one particular area or joint does not necessarily imply being flexible in another. Being "loose" in the upper body does not mean you will have a "loose" lower body. Furthermore, according to `SynerStretch', flexibility in a joint is also "specific to the action performed at the joint (the ability to do front splits doesn't imply the ability to do side splits even though both actions occur at the hip)." ------------------------------ Subject: 2.1 - Types of Flexibility Many people are unaware of the fact that there are different types of flexibility. These different types of flexibility are grouped according to the various types of activities involved in athletic training. The ones which involve motion are called "dynamic" and the ones which do not are called "static". The different types of flexibility (according to Kurz) are: "dynamic flexibility" Dynamic flexibility (also called "kinetic flexibility") is the ability to perform dynamic (or kinetic) movements of the muscles to bring a limb through its full range of motion in the joints. "static-active flexibility" Static-active flexibility (also called "active flexibility") is the ability to assume and maintain extended positions using only the tension of the agonists and synergists while the antagonists are being stretched (See "1.4 - Cooperating Muscle Groups"). For example, lifting the leg and keeping it high without any external support (other than from your own leg muscles). "static-passive flexibility" Static-passive flexibility (also called "passive flexibility") is the ability to assume extended positions and then maintain them using only your weight, the support of your limbs, or some other apparatus (such as a chair or a barre). Note that the ability to maintain the position does not come solely from your muscles, as it does with static-active flexibility. Being able to perform the splits is an example of static-passive flexibility. Research has shown that active flexibility is more closely related to the level of sports achievement than is passive flexibility. Active flexibility is harder to develop than passive flexibility (which is what most people think of as "flexibility"); not only does active flexibility require passive flexibility in order to assume an initial extended position, it also requires muscle strength to be able to hold and maintain that position. ------------------------------ Subject: 2.2 - Factors Limiting Flexibility According to Gummerson, flexibility (he uses the term "mobility") is affected by the following factors: * Internal influences - the type of joint (some joints simply aren't meant to be flexible) - the internal resistance within a joint - bony structures which limit movement - the elasticity of muscle tissue (muscle tissue that is scarred due to a previous injury is not very elastic) - the elasticity of tendons and ligaments (ligaments do not stretch much and tendons should not stretch at all) - the elasticity of skin (skin actually has some degree of elasticity, but not much) - the ability of a muscle to relax and contract to achieve the greatest range of movement - the temperature of the joint and associated tissues (joints and muscles offer better flexibility at body temperatures that are 1 to 2 degrees higher than normal) * External influences - the temperature of the place where one is training (a warmer temperature is more conducive to increased flexibility) - the time of day (most people are more flexible in the afternoon than in the morning, peaking from about 2:30pm-4pm) - the stage in the recovery process of a joint (or muscle) after injury (injured joints and muscles will usually offer a lesser degree of flexibility than healthy ones) - age (pre-adolescents are generally more flexible than adults) - gender (females are generally more flexible than males) - one's ability to perform a particular exercise (practice makes perfect) - one's commitment to achieving flexibility - the restrictions of any clothing or equipment Some sources also the suggest that water is an important dietary element with regard to flexibility. Increased water intake is believed to contribute to increased mobility, as well as increased total body relaxation. Rather than discuss each of these factors in significant detail as Gummerson does, I will attempt to focus on some of the more common factors which limit one's flexibility. According to `SynerStretch', the most common factors are: bone structure, muscle mass, excess fatty tissue, and connective tissue (and, of course, physical injury or disability). Depending on the type of joint involved and its present condition (is it healthy?), the bone structure of a particular joint places very noticeable limits on flexibility. This is a common way in which age can be a factor limiting flexibility since older joints tend not to be as healthy as younger ones. Muscle mass can be a factor when the muscle is so heavily developed that it interferes with the ability to take the adjacent joints through their complete range of motion (for example, large hamstrings limit the ability to fully bend the knees). Excess fatty tissue imposes a similar restriction. The majority of "flexibility" work should involve performing exercises designed to reduce the internal resistance offered by soft connective tissues (See "1.3 - Connective Tissue"). Most stretching exercises attempt to accomplish this goal and can be performed by almost anyone, regardless of age or gender. ------------------------------ Subject: 2.2.1 - How Connective Tissue Affects Flexibility The resistance to lengthening that is offered by a muscle is dependent upon its connective tissues: When the muscle elongates, the surrounding connective tissues become more taut (See "1.3 - Connective Tissue"). Also, inactivity of certain muscles or joints can cause chemical changes in connective tissue which restrict flexibility. To quote M. Alter directly: A question of great interest to all athletes is the relative importance of various tissues in joint stiffness. The joint capsule (i.e., the saclike structure that encloses the ends of bones) and ligaments are the most important factors, accounting for 47 percent of the stiffness, followed by the muscle's fascia (41 percent), the tendons (10 percent), and skin (2 percent). However, most efforts to increase flexibility through stretching should be directed to the muscle fascia. The reasons for this are twofold. First, muscle and its fascia have more elastic tissue, so they are more modifiable in terms of reducing resistance to elongation. Second, because ligaments and tendons have less elasticity than fascia, it is undesirable to produce too much slack in them. Overstretching these structures may weaken the integrity of joints. As a result, an excessive amount of flexibility may destabilize the joints and *increase* an athlete's risk of injury. When connective tissue is overused, the tissue becomes fatigued and may tear, which also limits flexibility. When connective tissue is unused or under used, it provides significant resistance and limits flexibility. The elastin begins to fray and loses some of its elasticity, and the collagen increases in stiffness and in density. Aging has some of the same effects on connective tissue that lack of use has. ------------------------------ Subject: 2.2.2 - How Aging Affects Flexibility With appropriate training, flexibility can, and should, be developed at all ages. This does not imply, however, that flexibility can be developed at the same rate by everyone. In general, the older you are, the longer it will take to develop the desired level of flexibility. Hopefully, you'll be more patient if you're older. According to M. Alter, the main reason we become less flexible as we get older is a result of certain changes that take place in our connective tissues: The primary factor responsible for the decline of flexibility with age is certain changes that occur in the connective tissues of the body. Interestingly, it has been suggested that exercise can delay the loss of flexibility due to the aging process of dehydration. This is based on the notion that stretching stimulates the production or retention of lubricants between the connective tissue fibers, thus preventing the formation of adhesions. M. Alter further states that some of the physical changes attributed to aging are the following: * An increased amount of calcium deposits, adhesions, and cross-links in the body * An increase in the level of fragmentation and dehydration * Changes in the chemical structure of the tissues. * Loss of "suppleness" due to the replacement of muscle fibers with fatty, collagenous fibers. This does *not* mean that you should give up trying to achieve flexibility if you are old or inflexible. It just means that you need to work harder, and more carefully, for a longer period of time when attempting to increase flexibility. Increases in the ability of muscle tissues and connective tissues to elongate (stretch) can be achieved at any age. ------------------------------ Subject: 2.3 - Strength and Flexibility Strength training and flexibility training should go hand in hand. It is a common misconception that there must always be a trade-off between flexibility and strength. Obviously, if you neglect flexibility training altogether in order to train for strength then you are certainly sacrificing flexibility (and vice versa). However, performing exercises for both strength and flexibility need not sacrifice either one. As a matter of fact, flexibility training and strength training can actually enhance one another. ------------------------------ Subject: 2.3.1 - Why Bodybuilders Should Stretch One of the best times to stretch is right after a strength workout such as weightlifting. Static stretching of fatigued muscles (See "3.5 - Static Stretching") performed immediately following the exercise(s) that caused the fatigue, helps not only to increase flexibility, but also enhances the promotion of muscular development (muscle growth), and will actually help decrease the level of post-exercise soreness. Here's why: After you have used weights (or other means) to overload and fatigue your muscles, your muscles retain a "pump" and are shortened somewhat. This "shortening" is due mostly to the repetition of intense muscle activity that often only takes the muscle through part of its full range of motion. This "pump" makes the muscle appear bigger. The "pumped" muscle is also full of lactic acid and other by-products from exhaustive exercise. If the muscle is not stretched afterward, it will retain this decreased range of motion (it sort of "forgets" how to make itself as long as it could) and the buildup of lactic acid will cause post-exercise soreness. Static stretching of the "pumped" muscle helps it to become "looser", and to "remember" its full range of movement. It also helps to remove lactic acid and other waste-products from the muscle. While it is true that stretching the "pumped" muscle will make it appear visibly smaller, it does not decrease the muscle's size or inhibit muscle growth. It merely reduces the "tightness" (contraction) of the muscles so that they do not "bulge" as much. Also, strenuous workouts will often cause damage to the muscle's connective tissue. The tissue heals in 1 to 2 days but it is believed that the tissues heal at a shorter length (decreasing muscular development as well as flexibility). To prevent the tissues from healing at a shorter length, physiologists recommend static stretching after strength workouts. ------------------------------ Subject: 2.3.2 - Why Contortionists Should Strengthen You should be "tempering" (or balancing) your flexibility training with strength training (and vice versa). Do not perform stretching exercises for a given muscle group without also performing strength exercises for that same group of muscles. Judy Alter, in her book `Stretch and Strengthen', recommends stretching muscles after performing strength exercises, and performing strength exercises for every muscle you stretch. In other words: "Strengthen what you stretch, and stretch after you strengthen!" The reason for this is that flexibility training on a regular basis causes connective tissues to stretch which in turn causes them to loosen (become less taut) and elongate. When the connective tissue of a muscle is weak, it is more likely to become damaged due to overstretching, or sudden, powerful muscular contractions. The likelihood of such injury can be prevented by strengthening the muscles bound by the connective tissue. Kurz suggests dynamic strength training consisting of light dynamic exercises with weights (lots of reps, not too much weight), and isometric tension exercises. If you also lift weights, dynamic strength training for a muscle should occur *before* subjecting that muscle to an intense weightlifting workout. This helps to pre-exhaust the muscle first, making it easier (and faster) to achieve the desired overload in an intense strength workout. Attempting to perform dynamic strength training *after* an intense weightlifting workout would be largely ineffective. If you are working on increasing (or maintaining) flexibility then it is *very* important that your strength exercises force your muscles to take the joints through their full range of motion. According to Kurz: Repeating movements that do not use a full range of motion in the joints (e.g., bicycling, certain techniques of Olympic weightlifting, pushups) can cause a shortening of the muscles surrounding the joints of the working limbs. This shortening is a result of setting the nervous control of length and tension in the muscles at the values repeated most often or most strongly. Stronger stimuli are remembered better. ------------------------------ Subject: 2.4 - Overflexibility It is possible for the muscles of a joint to become too flexible. According to `SynerStretch': There is a tradeoff between flexibility and stability. The looser you get, the less support offered to the joints by their adjacent muscles. Excessive flexibility can be just as much of a liability as not enough flexibility. Either one increases your risk of injury. Once a muscle has reached its absolute maximum length, attempting to stretch the muscle further only serves to stretch the ligaments and put undue stress upon the tendons (two things that you do *not* want to stretch). Ligaments will tear when stretched more than 6% of their normal length. Tendons are not even supposed to be able to lengthen. Even when stretched ligaments and tendons do not tear, loose joints and/or a decrease in the joint's stability can occur (thus vastly increasing your risk of injury). Once you have achieved the desired level of flexibility for a muscle or set of muscles and have maintained that level for a solid week, you should discontinue any isometric or PNF stretching of that muscle until some of its flexibility is lost (See "3.6 - Isometric Stretching"), and See "3.7 - PNF Stretching"). ------------------------------ Subject: 3 - 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 ------------------------------ Subject: 3.1 - 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 "1.6.2 - The Stretch Reflex"). ------------------------------ Subject: 3.2 - 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). (See "4.1 - Warming Up"). 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. ------------------------------ Subject: 3.3 - 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 (See "1.4 - Cooperating Muscle Groups"). 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 (See "1.6.4 - 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. ------------------------------ Subject: 3.4 - 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 (See "4.12 - Pain and Discomfort"). Relaxed stretching is also very good for "cooling down" after a workout and helps reduce post-workout muscle fatigue, and soreness. (See "4.2 - Cooling Down"). ------------------------------ Subject: 3.5 - 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. ------------------------------ Subject: 3.6 - 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 (See "1.5 - Types of Muscle Contractions"). 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. ------------------------------ Subject: 3.6.1 - How Isometric Stretching Works Recall from our previous discussion (See "1.2.1 - How Muscles Contract") 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 (See "1.6 - What Happens When You Stretch"). 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 (See "1.6.2 - The Stretch Reflex") and triggers the lengthening reaction (See "1.6.3 - 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 (See "1.6.1 - Proprioceptors"): 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. ------------------------------ Subject: 3.7 - 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 (See "3.4 - Passive Stretching") and isometric stretching (See "3.6 - 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 (See "1.6.2 - The 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 (See "1.6.4 - 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 (See "3.6 - 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. ------------------------------ Subject: 3.7.1 - 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 (See "3.6.1 - How Isometric Stretching Works"). 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 (See "3.6.1 - How Isometric Stretching Works"), 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 (See "1.2.2 - Fast and Slow Muscle Fibers"). This makes it harder for the fatigued muscle fibers to contract in resistance to a subsequent stretch (See "1.6.2 - The Stretch Reflex"). 3. The tension generated by the contraction activates the golgi tendon organ (See "1.6.1 - Proprioceptors"), which inhibits contraction of the muscle via the lengthening reaction (See "1.6.3 - 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. ------------------------------ -- Brad_Appleton@ivhs.mot.com Motorola PNSB, Northbrook, IL USA "And miles to go before I sleep." DISCLAIMER: I said it, not my employer!