Man’s interest in flexibility is by no means a modern development. The importance of flexibility and its practice is evident from Roman times in the training of Gladiators, and in more recent times World War I injuries spurred the study of orthopedics. Specifically, as injured soldiers returned from war many were compromised in basic daily function because of loss of flexibility that occurred from war injuries. It was observed how this limited one’s activities and the practice of restoring function began. The interest in flexibility was heightened again in the 1950s, 60s, and 70s when standardized fitness tests were developed and children were performing poorly on flexibility and strength measures. Fast forwarding to today restoration of range of motion is a primary goal of therapists when rehabilitating musculoskeletal injuries and it is often the most limiting factor in recovery from a musculoskeletal injury. Beyond that, we now have science to demonstrate the loss of flexibility and muscle function with age which leads to loss of independence and thus the primary goal of many exercise programs is to maintain muscular strength and flexibility.(Kraus, H., & Hirschland, R. P. 1954).

But have you ever wondered why some people are more flexible than others? Is it because they stretch more, or is it a genetic trait? You probably know someone who is quite flexible but who rarely stretches. Are females more flexible than males? How do you become more flexible? These are all important questions regarding muscle flexibility. We can accurately answer some of these questions but other answers are less clear. This chapter will provide some insights into the numerous factors that influence flexibility.

Flexibility is basically described as the total range of motion (ROM) around a joint (or group of joints such as the spine). Thus the terms flexibility and ROM are often used interchangeably. One problem in the literature is the inconsistent use of terms such as flexibility, stretching, range of motion, and so on. Many other terms are also related to overall flexibility and these terms along with definitions are presented below in Table 8.1. In more scientific term, flexibility is defined as the intrinsic property of body tissues. However, while both intrinsic and extrinsic factors relate to flexibility, the intrinsic component is clearly more important. ROM is highly variable from joint to joint and from person to person. Flexibility as a term is used by many practitioners, including strength and conditioning coaches, athletic trainers, physical therapists, doctors, and chiropractors, etc. For this reason there are often differences in what each practitioner means when they refer to flexibility. Thus, we must consider the setting in which the term flexibility is being used, such as a clinic, running track, or training room.

Flexibility is advocated as promoting multiple healthy outcomes. In general, flexibility declines with age and injury.

The benefits of stretching include:

Decreased risk of low back pain

Reduced muscle soreness post exercise

Reduced risk of musculoskeletal injury

Increased functional range of motion

Increased comfort in activities of daily living

Improved muscular efficiency

Faster recovery from injury

Improved postural alignment

Improved mobility

Improved self perception with movement

Adapted from Mc Hugh & Gleim (1998)

Alkylosis: – Pathologically low flexibility (may be whole body or joint specific).

Compliance: – How easy the muscle lengthens or stretches.

Deformation: – The ability of the muscle to change shape (stretch) and then return to normal.

Elasticity: – The ability of a material to resist deformation from force and then return to normal state.

Flexibility: – The intrinsic property of body tissues that determine ROM without injury.

Hypermobility: – Excessive joint (or group of joints) ROM.

Stiffness: – A measure of a material’s elasticity, often defined as the ration of force to elongation.

Viscoelastic: – Complex mechanical behavior of a material because the resistive force in the material is dependant on elongation (elastic) and the rate (viscous) at which the force is applied.

Yield Point: – the point beyond which deformation becomes permanent (or muscle is torn).

Stretch Tip number 1(see illustrations).

Your father is interested in improving his range of motion in his shoulders. Can you suggest 3 basic exercises?

a. Large arm circles. Stand up tall and swing both arms in large circles forward and backwards for 10 rotations each.

b. Full arm wall press: Stand against a wall with your arm straight back and against the wall. Keep your arm against the wall and gently turn your body away from the wall slightly and hold fro 20 seconds. Repeat on each side.

c. Lie on your back, put your arms out straight, hands overlapping, and place on the floor behind your head. Hold for 20 seconds

(1)Anatomy and Physiology of Stretching & Flexibility

The anatomy and physiology of stretching involves multiple components: the design of the musculoskeletal system, muscle composition and connective tissue. Additionally, we must consider other co-contracting and synergistic muscle groups, the types of muscle actions and the forces produced. Let’s look at the role of these components in stretching.

Design of the Musculoskeletal System: The muscles and bones naturally comprise the musculoskeletal system. The muscles are often viewed as cords attached to levers to facilitate movement and posture. The muscles pull on the bones generating tension and consequently movement. Bones are connected to bones via ligaments which are not very flexible. The muscles are attached to the bone via tendons which are more flexible than ligaments, as is the muscle itself. Muscles vary in shape and size depending upon their role. Generally longer muscles are more flexible with a greater range of motion.

Muscle Composition: While the body contains several types of muscle, such as skeletal, heart, and digestive, their basic structure is the same. That is, the muscle composition is similar in that they all contain fascicles, fiber, myofibrils, sarcomeres, and contractile proteins. In skeletal muscle, a fibrous connective tissue called the epimysium covers the body’s more than 430 skeletal muscles. Inside the epimysium the muscle fibers are bound in bundles called fascicles which often contain 100-150 fibers. Within fascicles, muscle fibers are separated by the endomysium. Outside of the fascicles lies the perimysium which separates the fascicles wrapped in the epimysium. The muscle fiber itself is made up of proteins called actin and myosin (contractile proteins) and these proteins are arranged longitudinally within the smallest component of the muscle fiber, the sarcomere. It is the sarcomere that actually shortens and lengthens when we perform a contraction.

Fascicles: Bundles of muscle fibers.

Fiber: Cylindrical cells that sometimes run the length of the muscle.

Myofibril: The inside of a muscle fiber that contain the contractile proteins, actin and myosin.

Sarcomere: The smallest contractile unit of skeletal muscle.

Connective Tissue: A main factor affecting ROM is connective tissue. Connective tissue can be found all around muscles. Connective tissue contains two types of fiber called collagenous connective tissue and elastic connective tissue. Collagenous tissue comprises mainly collagen, which are extracellular, related proteins that provide tensile strength. Elastic tissue comprises mostly elastin, a yellow scleroprotein that provides elasticity. In general, the greater the amount of elastic connective tissue surrounding a joint; the greater the elasticity or ROM will be around that joint.

Muscle Groups: The way in which a muscle group interacts with the other co-contracting muscles in its group can also influence ROM. For example, with knee flexion we have hamstring contractions, gastrocnemius lengthening (or shortening), gluteal shortening, and so on. At the same time the quadriceps relax so as not to impede the flexibility. This is referred to as reciprocal inhibition (more about this later). It is also referred to as the agonist/antagonist relationship. Thus the degree of resistance or compliance of an opposing or synergistic muscle can increase or decrease one’s ROM.

Insert Illustration showing agonist-antagonist relationship

Research Box

Effects of Stretching on Passive Muscle Tension and Response to Eccentric Exercise. La Roche DA and Connolly DA. 2006 (vol 34, 6, 1000-1007). American Journal of Sports Medicine.

The purpose of this study was to assess if 4 weeks of stretching could reduce the risk of muscle injury following eccentric exercise. 29 subjects were assigned to a static stretching, ballistic stretching, or control group. Baseline measurements for dynamic range of motion, stiffness, peak torque, and soreness were recorded. Subjects then performed a stretching program for s total of 3600 seconds over 4 weeks in their assigned group. Baseline tested was then repeated with an eccentric task designed to cause muscle damage added after day 1. Both stretching groups increased their range of motion and stretch tolerance following the 4 weeks of stretching. After eccentric exercise both stretching groups had greater range of motion and less pain than the control group. The authors concluded that 4 weeks of stretching maintains range of motion following eccentric exercise.

The Action of Stretching

When you stretch your muscle the origin of the stretch is in the sarcomere. As the sarcomere contracts, the area of overlap between thick and thin filaments increases and this facilitates increased forced production. Consequently, as the muscle stretches this area of overlap decreases allowing muscle elongation. This is often referred to as “Sarcomeres in series.” When the muscle reaches its maximum resting length the stretch tension transfers to the connective tissue. Because connective tissue is less pliable than muscle tissue, the relative stretch is considerably decreased. When we stretch, not all fibers are stretched and the length of the muscle actually depends upon the number of stretched fibers. As we increase the length of the muscle more fibers are stretched. The ultimate length of the stretch is also influenced by other feedback from proprioceptors, the stretch reflex and lengthening reaction. Let’s look at what these are!

(3)Proprioceptors

Anytime we move our limbs around we receive feedback information about the position and length of our muscles and limbs. This information about the musculoskeletal system is relayed back to the central nervous system via proprioceptors. Proprioception is a spatial awareness of one’s body movement and position. Proprioceptors are sometimes referred to as mechanoreceptors and they specifically detect changes in position, force and tension of muscles. When we stretch a muscle the proprioceptors provide feedback about the length of the muscle, especially pain and discomfort when the muscle is stretched too far. The primary proprioceptors involved in stretching are called muscle spindles or stretch receptors. Also involved are golgi tendon organs which are found in the tendon at the end of muscle. They provide information specifically on positional changes and pressure or tension. Golgi tendon organs provide information about the change in muscle tension and also the rate of change in tension (sometimes called rate of force development). Thus, together they provide feedback about when our muscles are lengthening or are experiencing too much force.

(3)Stretch Reflex

Naturally, when the muscle lengthens so too do the muscle spindles. The information provided by the spindles triggers what is called the stretch reflex or myotatic reflex. This causes the muscle to try and shorten (it basically resists lengthening). This stretch reflex contains both a static and a dynamic component that relate to the initial increase in length and the duration of the stretch. These are called the lengthening reaction and the reciprocal inhibition.

(3)The Lengthening Reaction

When we stretch and induce the stretch reflexes causing the muscle to contract, tension is produced at the musculotendonous junction (this is where the GTO is located). As the tension increases it reaches a threshold which causes a “lengthening reaction” which prevents the muscle from contracting and actually causes them to relax. (This is often referred to as the inverse myotatic reflex or autogenic inhibition.) This action is part of the reason that exercise prescription for stretching advocates holding a stretch for at least 15-20 seconds.

(3)Reciprocal Inhibition

A final consideration in this section is the action called reciprocal inhibition. In reciprocal inhibition the antagonists are essentially neutralized and prevented from contracting thereby not impeding the stretch of the agonist. Practicing how to voluntarily relax your antagonist can increase your stretch response in the agonists.

(1)Types of Stretching

Stretching can take many forms, last for various durations, and have both negative and positive effects on athletic performance. Stretching can be performed statically or dynamically. If a stretch is performed dynamically, it directly affects dynamic flexibility. If it is done statically, it will directly affect static flexibility. There is also some crossover effect between the types of stretching. There are numerous ways to stretch. The following is a list of stretching techniques.

Static Type Stretching

Static stretching basically involves a form of stretching whereby the muscle is lengthened and then held in that lengthened position for a pre-determined period of time. The following are types of dynamic stretching.

Static Holding Stretching involves stretching ones own muscle as far as comfortable and then holding the stretch for 10-30 seconds.

Passive Stretching involves someone else stretching your muscle and applying the 10-30 second hold. This method usually results in a further stretch than individual static stretching. Sometimes this technique is used without someone else when you use another body part to stretch a particular muscle group. A simple example is stretching your quadriceps by holding onto your foot and pulling up towards your back. Sometimes you will see passive stretching called relaxed stretching or static-passive stretching.

Proprioceptive Neuromuscular Facilitation Stretching (PNF) is a popular and effective method of rapidly increasing ROM. PNF combines both static and dynamic components by having isometric agonist contraction, relaxation and contraction again. It normally requires a partner and is sometimes call partner assisted stretching. In basic PNF the individual stretches an agonist muscle as far as possible (a partner can help stretch further.) This initial stretch is held for about 10 seconds and then an antagonist contraction follows for 5-10 seconds. Following this the original agonist is then stretched again and the cycle repeated. This cycle should be repeated about 3-5 times on each muscle, with the muscle being stretched a little farther each time.

Isometric stretching is somewhat of a combination of PNF and static stretching. This method requires the muscle to contract at the end of the range of motion and so the muscle being stretched is also the agonist. A common example is a calf stretch where one pushes against the wall creating both force and stretch in the calf at the same time. An additional advantage of isometric stretching is that it can also increase strength.

Dynamic Type Stretching

Dynamic stretching basically involves a form of stretching whereby the muscle is lengthened and shortened at various speeds without the muscle being held in the lengthened position for any period of time. The following are types of dynamic stretching.

Ballistic stretching uses a limb’s momentum to push it beyond its normal ROM. Sometimes added weight can be held to increase the stretch. This stretching involves limbs swinging through their ROM back and forth for about 10 repetitions. This stretching has traditionally been viewed as unsafe. However, it is effective if progress is done slowly and few injuries have actually been reported. One concern with this stretch is that the muscles do not have enough time in the lengthened position to adapt to the stretch and may in fact invoke the stretch reflex causing greater tightness.

Dynamic stretching is a progressive stretching technique involving slow increases in ROM and speed. In contrast to ballistic stretching, dynamic stretching is more controlled and progressive. Dynamic stretching does not contain bouncing or ballistic movement. Dynamic stretches are commonly used in team sport settings or where speed movements are important.

Active stretching is not commonly practiced as it is difficult and uncomfortable to a degree. In this technique a muscle is held only by the antagonist muscle in a certain position at the limit of motion for about 10 seconds. For example, lifting your leg straight up and holding it. Yoga uses many of these types of stretching.

Application Question: Can you improve your flexibility if you are fifty or sixty years old?

Answer: Even elderly men and women over seventy years old can increase their flexibility (Brown et al. 2000; Lazowski et al. 1999). With strength training the elderly, even in their 90s, can increase their strength and muscle mass although not as fast and as much as young people, but they can (Fiatarone et al. 1990; Lexell et al. 1995), and the responsiveness to strength training determines the effectiveness of isometric stretches (the most intense stretches) as long as the structure of the person’s joints is not an obstacle.

Exercise Prescription for Stretching

The main reason advocated for the development of flexibility and its assessment is the reduction of injury. Interestingly, the literature does not support increased levels of static or dynamic flexibility reducing injury. It actually appears that people at both extremes of static flexibility may be at higher risk for musculoskeletal injuries and we don’t have mush information on the relationship between dynamic flexibility and injury. In general, it is agreed that flexibility is healthy and although most experts agree on the benefits of flexibility and stretching, precise guidelines for stretching do not clearly exist. There is wide variation in the type of stretching, duration of stretches and intensity. Many individuals stretch for only a few seconds whereas others may stretch for 50 minutes as in a yoga class. General guidelines by the American College of Sports Medicine (ACSM) recommend three days of stretching per week, holding stretches for 10-30 seconds and 3-5 stretches for each major muscle group. ACSM recommends static stretching for the majority of the population.

When is it best to stretch?

In general, muscle is more receptive to stretch when it is warmer. Therefore, it makes more sense to stretch your muscles following exercise. We must be careful and distinguish between stretching to improve ROM and warming up for performance. Human muscle stretches better at about 38.5° c. which is higher than normal body temperature. For this reason, post exercise is perhaps the best time to stretch.

Factors Influencing Flexibility

Many factors contribute to joint flexibility. Sometimes the factors influencing flexibility can be classified as intrinsic or extrinsic factors. Intrinsic factors apply to those musculoskeletal factors within the body such as ligaments and tendons, whereas extrinsic factors generally apply to factors such as age, gender, body build and so on. Generally, extrinsic factors are those that we cannot change.

Intrinsic Factors for Flexibility

While factors such as age and gender clearly play a role, the structure of the joint itself plays a major role in its own flexibility. Joints comprise various types of tissue and bone and these components differ in how they contribute to joint flexibility. Table 2 provides information on the relative contributions of soft tissue to joint ROM. Intrinsic factors specifically relate to the mechanical properties of the musculoskeletal variable. This varies between individuals and is affected by injury, race, muscle types and amount and others. In general, when we practice stretching we are seeking to make change to these intrinsic factors.

Extrinsic Factors for Flexibility

We can assume the intrinsic factors to be fairly consistent within individuals leaving a lot of room for the many extrinsic factors to influence joint flexibility. However, extrinsic factors usually explain variability between joints within individuals and overall flexibility between individuals and not all of them are changeable.

Gender: In general, females are more flexible than males across the lifespan. Several factors contribute to this increased flexibility such as lower muscle mass, different hormone concentration and anatomical variations in joint structure.

Age: flexibility tends to decrease with age usually beginning in the teenage years. With increasing age there is a decrease in elasticity of connective tissue surrounding both joints and muscles. For the most part this is attributed to decreased activity levels.

Temperature: Muscle and connective tissue are like most other materials, i.e. they are more pliable/flexible at warmer temperatures. Increasing body temperature through an appropriate “warm-up” increases the flexibility of the muscle and joint. Consequently, a decrease in body or muscle temperature decreases flexibility and may increase the risk of injury.

Habitual/Exercise Activity: Individuals normally preserve the required flexibility to perform tasks they perform on a daily or regular basis. Some scientists refer to this as “form follows function.” Therefore, individuals who exercise regularly and exercise their limbs through a full ROM tend to preserve flexibility better with age. A sedentary lifestyle is associated with decreased flexibility.

Injury: Injury is a common cause of loss of flexibility especially in the upper extremities. Joint injuries typically result in the deposition of collagen or scar tissue. Scar tissue in particular restricts the mobility of the joint. Joint injuries also result in inflammation that also restricts mobility. Following injury rehabilitation to specifically restore and increase ROM is extremely important to allow the joint to return to normal function.

Joint Structure/Type of Joint: Flexibility is specific to each joint and to the way in which the joint is designed. Ball and socket joints (triaxial) are much more mobile than glinglymus joints (uni-axial). Joints fall into one of four categories based on ROM, no movement (non-axial), uni-axial, bi-axial or triaxial. The structure of the joint is therefore a major determinant in a joint ROM.

Muscle Mass/Body Build: The role of muscle mass in flexibility while important is often over-emphasized. In general, well hypertrophied muscles of the upper body, e.g. chest and arms, can restrict movement. However, if muscles are developed through the entire ROM of the muscle, flexibility is often preserved. Male gymnasts are a good example of well hypertrophied muscle and high flexibility. Therefore, while muscle mass can play a role in diminishing flexibility, the negative effects can be minimized by ensuring full ROM during muscle contraction.

Pregnancy: Women generally increase their flexibility during pregnancy. The basic reason for this is to prepare for childbirth but also to allow greater ROM in the hip region. Specifically, the pelvic and hip joints increase in flexibility due to increased production levels of the hormone relaxin. This can also help alleviate discomfort with pregnancy associated Lordosis. Relaxin levels decrease following pregnancy.

Stretch tip number 2 (see illustrations)

Your friend complains of tight calf muscles following running, what can you recommend?

Stand with feet together, legs straight, on a step and let the heels hang over the edge. Hold this position for 20 seconds. Repeat several times.

Stand with feet together about 3 feet away from a wall. Place your hands on the wall and slowly bring your chest into the wall. Keep both heels on the floor. Hold this position for 20 seconds.

Stand with feet together about 3 feet away from the wall. With hands on the wall, bring one leg forward and push with the back leg keeping the heel on the ground. Repeat on each leg.

Flexibility and Athletic Performance

It is a widely held conception that flexibility improves athletic performance. However, the scientific literature does not consistently support this belief. There is great variation in the amount of flexibility required for successful performance between activities and even within activities, such as team sports, there is wide individual variation. Furthermore, decreased flexibility has been shown to improve running economy and thus decreased flexibility can in some cases improve performance. Some studies have shown that less stiff muscles are more effective in using the stored elastic energy that is developed during a stretch. However, we must be careful about when these stretches are initiated as recent evidence suggests that static stretching prior to activities requiring maximal contraction tends to cause a decrease in performance. Overall, the ability of increased flexibility to improve athletic performance is most likely restricted to those activities that actually require extreme ranges of flexibility such as gymnastics, figure skating etc. and a universal approach of requiring infinite flexibility in all athletes is not warranted.

Research Box

Dynamic versus Static Stretching Warm-up: The Effect on Power and Agility Performance. Mc Millian et al. 2006 (vol20, 3, 492-499). Journal of Strength and Conditioning Research.

30 subjects participated in a study to determine the effects of a dynamic warm-up (DWU), a static stretch warm-up (SWU), or no warm-up (NWU) on a T-shuttle agility test, an underhand medicine ball throw, and a 5-step jump. Testing took place over three consecutive days and the order of all tests and warm-ups was randomized. Each warm-up lasted for 10 minutes. The DWU comprised a series of exercise such as bend and reach, push-ups, squats, and skipping. The SWU comprised of exercises such as the overhead pull, quadriceps stretch, trunk flexion and extension. All stretches were performed once and held for 20-30 seconds. The NWU group did no exercises. Results showed significantly greater performances for all tests following a DWU. The performances did not differ between the SWU and NWU. The authors conclude that the use of SWU should be reassessed when preceding athletic performance.

Measurement of Flexibility

Several basic flexibility tests exist such as sit and reach for hamstrings and low back and shoulder rotation test for shoulders. Since flexibility varies between joints, comprehensive flexibility assessment would have to assess many joints. This is not really possible and so one typically selects a few major joints and muscles such as low back and hamstrings, calf and Achilles, and shoulders. Simple tests for these assessments as well as more detailed laboratory practices are described at the end of the chapter. Any measurement of flexibility should be based on sound and accepted testing procedures. For the most part static flexibility tests are the most widely used and these are based on linear and angular measurements of the motion of the joint. All flexibility assessments should follow a standardized procedure whereby warm-up, and practice trials are all controlled.

Summary

After you read this chapter, you should be able to do the following:

Define flexibility and other relevant terms related to flexibility

Flexibility is basically the range of motion around a joint. It is influenced by many factors.

Flexibility is an important for overall health. It is important for basic daily function and comfort.

Flexibility varies between joints within individuals and between individuals.

List the factors affecting flexibility

Factors that influence flexibility are numerous and varied and can be classified as intrinsic or extrinsic.

Intrinsic factors include variables such as the tendon and muscle, whereas extrinsic factors include variables such as age, gender and activity levels.

Explain the techniques for improving and measuring flexibility.

There are many ways to stretch and improve flexibility. The most commonly prescribed method is static stretching for 10-30 seconds per muscle group.

Including safe and full ROM exercises into our daily routine is an excellent way to improve and preserve flexibility.

Flexibility should be measured at multiple sites and can be assessed using basic goniometry or a more simple test such as a sit and reach teat.

Summary

Flexibility is an important component in overall health and generally declines with age. There are many benefits including reduced risk of low back pain and increased functional range of motion. Flexibility varies between people and is affected by many variables. These factors are usually classified as intrinsic or extrinsic. When we stretch we are usually trying to change intrinsic factors. Flexibility usually takes two forms, static and dynamic, and we can stretch a muscle using either form. Most exercise prescription for flexibility advocates static stretching and involves holding a stretch for 10-30 seconds per muscle group. When we stretch or measure flexibility, it should be performed at multiple sites as flexibility tends to be site specific. The major joints to consider are the lower back, shoulders, and hamstrings.

Chapter Review

Flexibility Discussion Questions

Identify and describe 5 extrinsic factors that are known to influence flexibility!

What are the best approaches to improve flexibility?

What are the various musculoskeletal components that provide regulatory feedback to muscle stretch?

Can you differentiate between the roles of golgi tendon organs and muscle spindles?

Provide a short description for each of the following terms:

‘Sarcomeres in series’.

Stretch reflex.

Lengthening reaction.

Proprioceptors.

Autogenic inhibition.

Reciprocal inhibition.