1. Physiology of Stretching
The purpose of this chapter is to introduce youto some of the basic physiological concepts that come into play when amuscle is stretched. Concepts will be introduced initially with a generaloverview and then (for those who want to know the gory details) will bediscussed in further detail. If you aren’t all that interested in thisaspect of stretching, you can skip this chapter. Other sections will referto important concepts from this chapter and you can easily look them upon a "need to know" basis.
1.1.The Musculoskeletal System
Together, muscles and bones comprise what is calledthe "musculoskeletal system" of the body. The bones provide posture andstructural support for the body and the muscles provide the body with theability to move (by contracting, and thus generating tension). The musculoskeletalsystem also provides protection for the body’s internal organs. In orderto serve their function, bones must be joined together by something. Thepoint where bones connect to one another is called a "joint", and thisconnection is made mostly by "ligaments" (along with the help of muscles).Muscles are attached to the bone by "tendons". Bones, tendons, and ligamentsdo not possess the ability (as muscles do) to make your body move. Musclesare very unique in this respect.
Muscles vary in shape and in size, and serve many differentpurposes. Most large muscles, like the hamstrings and quadriceps, controlmotion. Other muscles, like the heart, and the muscles of the inner ear,perform other functions. At the microscopic level however, all musclesshare the same basic structure.
At the highest level, the (whole) muscle is composedof many strands of tissue called "fascicles". These are the strands ofmuscle that we see when we cut red meat or poultry. Each fascicle is composedof "fasciculi" which are bundles of "muscle fibers".
The muscle fibersare in turn composed of tens of thousands of thread-like "myofybrils",which can contract, relax, and elongate (lengthen). The myofybrils are(in turn) composed of up to millions of bands laid end-to-end called "sarcomeres".Each sarcomere is made of overlapping thick and thin filaments called "myofilaments".The thick and thin myofilaments are made up of "contractile proteins",primarily actin and myosin.
1.2.1.How Muscles Contract
The way in which all these various levels of the muscleoperate is as follows: Nerves connect the spinal column to the muscle.The place where the nerve and muscle meet is called the "neuromuscularjunction". When an electrical signal crosses the neuromuscular junction,it is transmitted deep inside the muscle fibers. Inside the muscle fibers,the signal stimulates the flow of calcium which causes the thick and thinmyofilaments to slide across one another. When this occurs, it causes thesarcomere to shorten, which generates force. When billions of sarcomeresin the muscle shorten all at once it results in a contraction of the entiremuscle fiber.
When a muscle fiber contracts, it contracts completely.There is no such thing as a partially contracted muscle fiber. Muscle fibersare unable to vary the intensity of their contraction relative to the loadagainst which they are acting. If this is so, then how does the force ofa muscle contraction vary in strength from strong to weak? What happensis that more muscle fibers are recruited, as they are needed, to performthe job at hand. The more muscle fibers that are recruited by the centralnervous system, the stronger the force generated by the muscular contraction.
1.2.2.Fast and Slow Muscle Fibers
The energy which produces the calcium flow in the musclefibers comes from "mitochondria", the part of the muscle cell that convertsglucose (blood sugar) into energy. Different types of muscle fibers havedifferent amounts of mitochondria. The more mitochondria in a muscle fiber,the more energy it is able to produce. Muscle fibers are categorizedinto "slow-twitch fibers" and "fast-twitch fibers". Slow-twitch fibers(also called "Type 1 muscle fibers") are slow to contract, but they arealso very slow to fatigue. Fast-twitch fibers are very quick to contractand come in two varieties: "Type 2A muscle fibers" which fatigue at anintermediate rate, and "Type 2B muscle fibers" which fatigue very quickly.The main reason the slow-twitch fibers are slow to fatigue is that theycontain more mitochondria than fast-twitch fibers and hence are able toproduce more energy. Slow-twitch fibers are also smaller in diameter thanfast-twitch fibers and have increased capillary blood flow around them.Because they have a smaller diameter and an increased blood flow, the slow-twitchfibers are able to deliver more oxygen and remove more waste products fromthe muscle fibers (which decreases their "fatigability").
These three muscle fiber types (Types 1, 2A, and2B) are contained in all muscles in varying amounts. Muscles that needto be contracted much of the time (like the heart) have a greater numberof Type 1 (slow) fibers. According to `HFLTA’:
When a muscle begins to contract, primarily Type1 fibers are activated first, then Type 2A, then 2B. This sequence of fiberrecruitment allows very delicate and finely tuned muscle responses to braincommands. It also makes Type 2B fibers difficult to train; most of theType 1 and 2A fibers have to be activated already before a large percentageof the 2B fibers participate.
`HFLTA’ further states that the the best way toremember the difference between muscles with predominantly slow-twitchfibers and muscles with predominantly fast-twitch fibers is to think of"white meat" and "dark meat". Dark meat is dark because it has a greaternumber of slow-twitch muscle fibers and hence a greater number of mitochondria,which are dark. White meat consists mostly of muscle fibers which are atrest much of the time but are frequently called on to engage in brief boutsof intense activity. This muscle tissue can contract quickly but is fastto fatigue and slow to recover. White meat is lighter in color than darkmeat because it contains fewer mitochondria.
Located all around the muscle and its fibers are "connectivetissues". Connective tissue is composed of a base substance and two kindsof protein based fiber. The two types of fiber are "collagenous connectivetissue" and "elastic connective tissue". Collagenous connective tissueconsists mostly of collagen (hence its name) and provides tensile strength.Elastic connective tissue consists mostly of elastin and (as you mightguess from its name) provides elasticity. The base substance is called"mucopolysaccharide" and acts as both a lubricant (allowing the fibersto easily slide over one another), and as a glue (holding the fibers ofthe tissue together into bundles). The more elastic connective tissue thereis around a joint, the greater the range of motion in that joint. Connectivetissues are made up of tendons, ligaments, and the fascial sheaths thatenvelop, or bind down, muscles into separate groups. These fascial sheaths,or "fascia", are named according to where they are located in the muscles:
- · "endomysium"- The innermost fascial sheath that envelops individual muscle fibers.· "perimysium"- The fascial sheath that binds groups of muscle fibers into individualfasciculi (See "1.2 – Muscle Composition").· "epimysium"- The outermost fascial sheath that binds entire fascicles (See "1.2 -Muscle Composition").
1.4.Cooperating Muscle GroupsWhen muscles cause a limb to move through the joint’srange of motion, they usually act in the following cooperating groups:
"agonists" These muscles cause themovement to occur. They create the normal range of movement in a jointby contracting. Agonists are also referred to as "prime movers" since theyare the muscles that are primarily responsible for generating the movement.
"antagonists" These muscles act inopposition to the movement generated by the agonists and are responsiblefor returning a limb to its initial position.
"synergists" These muscles perform,or assist in performing, the same set of joint motion as the agonists.Synergists are sometimes referred to as "neutralizers" because they helpcancel out, or neutralize, extra motion from the agonists to make surethat the force generated works within the desired plane of motion.
"fixators" These muscles provide thenecessary support to assist in holding the rest of the body in place whilethe movement occurs. Fixators are also sometimes called "stabilizers".
As an example, when you flex your knee, your hamstringcontracts, and, to some extent, so does your gastrocnemius (calf) and lowerbuttocks. Meanwhile, your quadriceps are inhibited (relaxed and lengthenedsomewhat) so as not to resist the flexion (See "1.6.4 – Reciprocal Inhibition").In this example, the hamstring serves as the agonist, or prime mover; thequadricep serves as the antagonist; and the calf and lower buttocks serveas the synergists. Agonists and antagonists are usually located on oppositesides of the affected joint (like your hamstrings and quadriceps, or yourtriceps and biceps), while synergists are usually located on the same sideof the joint near the agonists. Larger muscles often call upon their smallerneighbors to function as synergists.
The following is a list of commonly used agonist/antagonistmuscle pairs:
- · pectorals/latissimusdorsi (pecs and lats)
· anteriordeltoids/posterior deltoids (front and back shoulder)
· trapezius/deltoids(traps and delts)
· abdominals/spinalerectors (abs and lower-back)
· leftand right external obliques (sides)
· quadriceps/hamstrings(quads and hams)
1.5.Types of Muscle ContractionsThe contraction of a muscle does not necessarily implythat the muscle shortens; it only means that tension has been generated.Muscles can contract in the following ways:
"isometric contraction" This is a contractionin which no movement takes place, because the load on the muscle exceedsthe tension generated by the contracting muscle. This occurs when a muscleattempts to push or pull an immovable object.
"isotonic contraction" This is a contractionin which movement *does* take place, because the tension generated by thecontracting muscle exceeds the load on the muscle. This occurs when youuse your muscles to successfully push or pull an object.
Isotonic contractions are further divided into twotypes:
"concentric contraction" This is acontraction in which the muscle decreases in length (shortens) againstan opposing load, such as lifting a weight up.
"eccentric contraction" This is a contractionin which the muscle increases in length (lengthens) as it resists a load,such as pushing something down.
During a concentric contraction, the muscles thatare shortening serve as the agonists and hence do all of the work. Duringan eccentric contraction the muscles that are lengthening serve as theagonists (and do all of the work). (See "1.4 – Cooperating Muscle Groups").
The stretching of a muscle fiber begins with the sarcomere(See "1.2 Muscle Composition"), the basic unit of contraction in the musclefiber. As the contraction the muscles that are lengthening serve as theagonists (and do all of the work). (See "1.4 – Cooperating Muscle Groups").
When a muscle is stretched, some of its fibers lengthen,but other fibers may remain at rest. The current length of the entire muscledesarcomere contracts, the area of overlap between the thick and thin myofilamentsincreases. As it stretches, this area of overlap decreases, allowing themuscle fiber to elongate. Once the muscle fiber is at its maximum restinglength (all the sarcomeres are fully stretched), additional stretchingplaces force on the surrounding connective tissue (See "1.3 ConnectiveTissue"). As the tension increases, the collagen fibers in the connectivetissue align themselves along the same line of force as the tension. Hencewhen you stretch, the muscle fiber is pulled out to its full length sarcomereby sarcomere, and then the connective tissue takes up the remaining slack.When this occurs, it helps to realign any disorganized fibers in the directionof the tension. This realignment is what helps to rehabilitate scarredtissue back to health.
There are two kinds of muscle fibers: "intrafusalmuscle fibers" and "extrafusal muscle fibers". Extrafusil fibers are theones that contain myofibrils (See "1.2 – Muscle Composition") and are whatis usually meant when we talk about muscle fibers. Intrafusal fibers arealso called "muscle spindles" and lie parallel to the extrafusal fibers.Muscle spindles, or "stretch receptors", are the primary proprioceptorsin the muscle. Another proprioceptor that comes into play during stretchingis located in the tendon near the end of the muscle fiber and is calledthe "golgi tendon organ". A third type of proprioceptor, called a "paciniancorpuscle", is located close to the golgi tendon organ and is responsiblefor detecting changes in movement and pressure within the body.
When the extrafusal fibers of a muscle lengthen,so do the intrafusal fibers (muscle spindles). The muscle spindle containstwo different types of fibers (or stretch receptors) which are sensitiveto the change in muscle length and the rate of change in muscle length.When muscles contract it places tension on the tendons where the golgitendon organ is located. The golgi tendon organ is sensitive to the changein tension and the rate of change of the tension.
When the muscle is stretched, so is the muscle spindle(See "1.6.1 Proprioceptors"). The muscle spindle records the change inlength (and how fast) and sends signals to the spine which convey thisinformation. This triggers the "stretch reflex" (also called the "myotaticreflex") which attempts to resist the change in muscle length by causingthe stretched muscle to contract. The more sudden the change in musclelength, the stronger the muscle contractions will be (plyometric, or "jump",training is based on this fact). This basic function of the muscle spindlehelps to maintain muscle tone and to protect the body from injury.
One of the reasons for holding a stretch for a prolongedperiod of time is that as you hold the muscle in a stretched position,the muscle spindle habituates (becomes accustomed to the new length) andreduces its signaling. Gradually, you can train your stretch receptorsto allow greater lengthening of the muscles.
Some sources suggest that with extensive training,the stretch reflex of certain muscles can be controlled so that there islittle or no reflex contraction in response to a sudden stretch. Whilethis type of control provides the opportunity for the greatest gains inflexibility, it also provides the greatest risk of injury if used improperly.Only consummate professional athletes and dancers at the top of their sport(or art) are believed to actually possess this level of muscular control.188.8.131.52. Components of the StretchReflexThe stretch reflex has both a dynamic component anda static component. The static component of the stretch reflex persistsas long as the muscle is being stretched. The dynamic component of thestretch reflex (which can be very powerful) lasts for only a moment andis in response to the initial sudden increase in muscle length. The reasonthat the stretch reflex has two components is because there are actuallytwo kinds of intrafusal muscle fibers: "nuclear chain fibers", which areresponsible for the static component; and "nuclear bag fibers", which areresponsible for the dynamic component.
Nuclear chain fibers are long and thin, and lengthensteadily when stretched. When these fibers are stretched, the stretch reflexnerves increase their firing rates (signaling) as their length steadilyincreases. This is the static component of the stretch reflex.
Nuclear bag fibers bulge out at the middle, wherethey are the most elastic. The stretch-sensing nerve ending for these fibersis wrapped around this middle area, which lengthens rapidly when the fiberis stretched. The outer-middle areas, in contrast, act like they are filledwith viscous fluid; they resist fast stretching, then gradually extendunder prolonged tension. So, when a fast stretch is demanded of these fibers,the middle takes most of the stretch at first; then, as the outer-middleparts extend, the middle can shorten somewhat. So the nerve that sensesstretching in these fibers fires rapidly with the onset of a fast stretch,then slows as the middle section of the fiber is allowed to shorten again.This is the dynamic component of the stretch reflex: a strong signal tocontract at the onset of a rapid increase in muscle length, followed byslightly "higher than normal" signaling which gradually decreases as therate of change of the muscle length decreases.
When muscles contract (possibly due to the stretch reflex),they produce tension at the point where the muscle is connected to thetendon, where the golgi tendon organ is located. The golgi tendon organrecords the change in tension, and the rate of change of the tension, andsends signals to the spine to convey this information (See "1.6.1 – Proprioceptors").When this tension exceeds a certain threshold, it triggers the "lengtheningreaction" which inhibits the muscles from contracting and causes them torelax. Other names for this reflex are the "inverse myotatic reflex", "autogenicinhibition", and the "clasped-knife reflex". This basic function of thegolgi tendon organ helps to protect the muscles, tendons, and ligamentsfrom injury. The lengthening reaction is possible only because the signalingof golgi tendon organ to the spinal cord is powerful enough to overcomethe signaling of the m to stretch a muscle that is relaxed than to stretcha muscle that is contracting.
By taking advantage of the situations when reciprocalinhibition *does* occur, you can get a more effective stretch by inducingthe antagonists to relax during the stretch due to the contraction of theagonists. You also want to relax any muscles used as synergists by themuscle you are trying to stretch. For example, when you stretch your calf,you want to contract the shin muscles (the antagonists of the calf) byflexing your foot. However, the hamstrings use the calf as a synergistso you want to also relax the hamstrings by contracting the quadricep (i.e.,keeping your leg straight).
Flexibility is defined by Gummerson as "the absoluterange of movement in a joint or series of joints that is attainable ina momentary effort with the help of a partner or a piece of equipment."This definition tells us that flexibility is not something general butis specific to a particular joint
or set of joints. In other words, it is a myth thatsome people are innately flexible throughout their entire body. Being flexiblein one particular area or joint does not necessarily imply being flexiblein another. Being "loose" in the upper body does not mean you will havea "loose" lower body. Furthermore, according to `SynerStretch’, flexibilityin a joint is also "specific to the action performed at the joint (theability to do front splits doesn’t imply the ability to do side splitseven though both actions occur at the hip)."
2.1.Types of FlexibilityMany people are unaware of the fact that there are differenttypes of flexibility. These different types of flexibility are groupedaccording to the various types of activities involved in athletic training.The ones which involve motion are called "dynamic" and the ones which donot are called "static". The different types of flexibility (accordingto Kurz) are:
"dynamic flexibility" Dynamic flexibility(also called "kinetic flexibility") is the ability to perform dynamic (orkinetic) movements of the muscles to bring a limb through its full rangeof motion in the joints.
"static-active flexibility" Static-activeflexibility (also called "active flexibility") is the ability to assumeand maintain extended positions using only the tension of the agonistsand synergists while the antagonists are being stretched (See "1.4 – CooperatingMuscle Groups"). For example, lifting the leg and keeping it high withoutany external support (other than from your own leg muscles).
"static-passive flexibility" Static-passiveflexibility (also called "passive flexibility") is the ability to assumeextended positions and then maintain them using only your weight, the supportof your limbs, or some other apparatus (such as a chair or a barre). Notethat the ability to maintain the position does not come solely from yourmuscles, as it does with static-active flexibility. Being able to performthe splits is an example of static-passive flexibility.
Research has shown that active flexibility is moreclosely related to the level of sports achievement than is passive flexibility.Active flexibility is harder to develop than passive flexibility (whichis what most people think of as "flexibility"); not only does active flexibilityrequire passive flexibility in order to assume an initial extended position,it also requires muscle strength to be able to hold and maintain that position.
According to Gummerson, flexibility (he uses the term"mobility") is affected by the following factors:
- · the type of joint (some joints simply aren’tmeant to be flexible) – the internal resistance within a joint bony structureswhich limit movement· theelasticity of muscle tissue (muscle tissue that is scarred due to a previousinjury is not very elastic)· theelasticity of tendons and ligaments (ligaments do not stretch much andtendons should not stretch at all)· theelasticity of skin (skin actually has some degree of elasticity, but notmuch)· theability of a muscle to relax and contract to achieve the greatest rangeof movement· thetemperature of the joint and associated tissues (joints and muscles offerbetter flexibility at body temperatures that are 1 to 2 degrees higherthan normal)
- · the temperature of the place where oneis training (a warmer temperature is more conducive to increased flexibility)· thetime of day (most people are more flexible in the afternoon than in themorning, peaking from about 2:30pm-4pm)· thestage in the recovery process of a joint (or muscle) after injury (injuredjoints and muscles will usually offer a lesser degree of flexibility thanhealthy ones)· age(pre-adolescents are generally more flexible than adults) gender (femalesare generally more flexible than males)· one’sability to perform a particular exercise (practice makes perfect)· one’scommitment to achieving flexibility· therestrictions of any clothing or equipment
Some sources also the suggest that water is an importantdietary element with regard to flexibility. Increased water intake is believedto contribute to increased mobility, as well as increased total body relaxation.
Rather than discuss each of these factors in significantdetail as Gummerson does, I will attempt to focus on some of the more commonfactors which limit one’s flexibility. According to `SynerStretch’, themost 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 itspresent condition (is it healthy?), the bone structure of a particularjoint places very noticeable limits on flexibility. This is a common wayin which age can be a factor limiting flexibility since older joints tendnot to be as healthy as younger ones.
Muscle mass can be a factor when the muscle is soheavily developed that it interferes with the ability to take the adjacentjoints through their complete range of motion (for example, large hamstringslimit the ability to fully bend the knees). Excess fatty tissue imposesa similar restriction.
The majority of "flexibility" work should involveperforming exercises designed to reduce the internal resistance offeredby soft connective tissues (See "1.3 – Connective Tissue"). Most stretchingexercises attempt to accomplish this goal and can be performed by almostanyone, regardless of age or gender.2.2.1.How Connective Tissue Affects FlexibilityThe resistance to lengthening that is offered by a muscleis dependent upon its connective tissues: When the muscle elongates, thesurrounding connective tissues become more taut (See "1.3 – ConnectiveTissue"). Also, inactivity of certain muscles or joints can cause chemicalchanges in connective tissue which restrict flexibility. To quote M. Alterdirectly:
"A question of great interest to all athletesis the relative importance of various tissues in joint stiffness. The jointcapsule (i.e., the saclike structure that encloses the ends of bones) andligaments are the most important factors, accounting for 47 percent ofthe stiffness, followed by the muscle’s fascia (41 percent), the tendons(10 percent), and skin (2 percent). However, most efforts to increase flexibilitythrough stretching should be directed to the muscle fascia. The reasonsfor 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 thesestructures may weaken the integrity of joints. As a result, an excessiveamount of flexibility may destabilize the joints and *increase* an athlete’srisk of injury."
When connective tissue is overused, the tissue becomesfatigued and may tear, which also limits flexibility. When connective tissueis unused or under used, it provides significant resistance and limitsflexibility. The elastin begins to fray and loses some of its elasticity,and the collagen increases in stiffness and in density. Aging has someof the same effects on connective tissue that lack of use has.2.2.2.How Aging Affects FlexibilityWith appropriate training, flexibility can, and should,be developed at all ages. This does not imply, however, that flexibilitycan be developed at the same rate by everyone. In general, the older youare, 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 becomeless flexible as we get older is a result of certain changes that takeplace in our connective tissues:
The primary factor responsible for the decline offlexibility with age is certain changes that occur in the connective tissuesof the body. Interestingly, it has been suggested that exercise can delaythe loss of flexibility due to the aging process of dehydration. This isbased on the notion that stretching stimulates the production or retentionof lubricants between the connective tissue fibers, thus preventing theformation of adhesions.
M. Alter further states that some of the physicalchanges attributed to aging are the following:
- · Anincreased amount of calcium deposits, adhesions, and cross-links in thebody· An increasein the level of fragmentation and dehydration· Changesin the chemical structure of the tissues.· Lossof "suppleness" due to the replacement of muscle fibers with fatty, collagenousfibers.
This does not mean that you should give up tryingto achieve flexibility if you are old or inflexible. It just means thatyou need to work harder, and more carefully, for a longer period of timewhen attempting to increase flexibility. Increases in the ability of muscletissues and connective tissues to elongate (stretch) can be achieved atany age.2.3.Strength and FlexibilityStrength training and flexibility training should gohand in hand. It is a common misconception that there must always be atrade-off between flexibility and strength. Obviously, if you neglect flexibilitytraining altogether in order to train for strength then you are certainlysacrificing flexibility (and vice versa). However, performing exercisesfor both strength and flexibility need not sacrifice either one. As a matterof fact, flexibility training and strength training can actually enhanceone another.2.3.1.Why Bodybuilders Should StretchOne of the best times to stretch is right after a strengthworkout 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 alsoenhances the promotion of muscular development (muscle growth), and willactually help decrease the level of post-exercise soreness. Here’s why:
After you have used weights (or other means) tooverload and fatigue your muscles, your muscles retain a "pump" and areshortened somewhat. This "shortening" is due mostly to the repetition ofintense muscle activity that often only takes the muscle through part ofits full range of motion. This "pump" makes the muscle appear bigger. The"pumped" muscle is also full of lactic acid and other by-products fromexhaustive exercise. If the muscle is not stretched afterward, it willretain this decreased range of motion (it sort of "forgets" how to makeitself as long as it could) and the buildup of lactic acid will cause post-exercisesoreness. Static stretching of the "pumped" muscle helps it to become "looser",and to "remember" its full range of movement. It also helps to remove l