Greater Flexibility

Related Terms

  • Active stretching, agonist muscle, antagonist muscle, ballistic stretching, delayed-onset muscle soreness (DOMS), dynamic stretching, flexibility, isometric contractions, isometric stretching, isotonic contractions, muscle tone, myotatic reflex, passive stretching, proprioceptive neuromuscular facilitation (PNF), range of motion, sacroiliac instability, soft tissue, soft-tissue length, static stretching, static-active stretching, static-passive stretching, stretch reflex, stretching, stretch-shortening cycle.

Background

  • Overview: Flexibility is the ability to move a joint through a range of motion without pain.
  • Range of motion is the movement of a joint or body segment from its starting position to its ending position.
  • Stretching is the movement of a body segment in a way that lengthens the shortened soft tissues, thus increasing flexibility. Soft tissues include muscles, fat, and fibrous tissue.
  • Performance improvements from stretching may include more force production, increased speed, and better jumping ability. In some cases, stretching may relieve pain.
  • In a sports context, stretching refers to a set of exercises often used as part of the warm-up routine before practice or competition. Such stretching often involves moving body segments deliberately, often slowly, to the limit of their range of motion, holding them at that limit for a period of time, then returning to rest.
  • In a clinical environment, stretching is used during physical therapy or occupational therapy to restore range of motion after an injury.
  • One way to isolate the history of stretching from the history of sports is to examine sports that especially emphasize extending the individual's range of motion, such as martial arts. A sports physician affiliated with the U.S. Department of Defense's Military Health System pegged the origin of martial arts as far back as 5000 BC. Gymnastics began in 500-700 BC. Yoga has been practiced since about 3000 BC.
  • Despite broad acknowledgement that lack of flexibility may be a risk factor for injury, literature reviews by several sports-medicine researchers found no association between stretching and injury prevention in athletes.
  • Some research suggests that fitness in general is more important than stretching for reducing the risk of injury. (The U.S. Department of Health and Human Services defines physical fitness as a set of attributes that people have or achieve relating to their ability to perform physical activity.) Also, research suggests that stretching in order to increase the range of motion beyond what is needed to participate in one's sport may not be beneficial and may actually cause injury and decrease performance.
  • The mechanics of stretching: The word stretch describes a physiological activity in the body.
  • Nerve impulses: Movement occurs when nerve impulses from the brain are delivered to sensors called motor neurons, which are attached to special stretch-sensitive muscle spindles near tendons. (Tendons attach muscles to bones.)
  • Muscle contraction/muscle stretching: In response to a stimulus, specialized nerve cells known as motor neurons cause the muscle to contract. The agonist muscle is primarily responsible for movement. As the agonist muscle contracts, the muscle that opposes it, the antagonist muscle, is stretched.
  • Stretch reflex: Motor neurons sense this muscle stretch and send signals to the spinal cord, prompting a "stretch," or myotatic, reflex. A stretch reflex causes the stretched muscle to contract.
  • Even though the initial movement may have been a conscious movement, initiated by a signal from the brain, the stretch reflex is unconscious, delivered by the spinal cord. This "shortcut" allows the fastest possible reaction time. Fast reaction time is important in allowing speedy adjustments to changing conditions. Fast reaction time also helps prevent the antagonist muscles from being injured by excessive stretching. In addition to helping prevent injury, the stretch reflex aids in keeping muscles toned by prompting tension between the agonist muscles and the antagonist muscles. The stretch reflex is central to flexibility training because altering the stretch reflex increases the individual's range of motion.
  • Types of flexibility and stretching:
  • Flexibility: There are three principal types of flexibility: dynamic, static, and passive.
  • Dynamic flexibility: Dynamic flexibility is the ability to move a body segment within a range of motion. Dynamic flexibility accounts for the increase in resistance as the body segment moves through its range of motion. Medical professionals measure dynamic flexibility in terms of stiffness, which is the ratio of force to elongation.
  • Static flexibility: Static flexibility, sometimes called static-active flexibility, is the ability to stretch an antagonist muscle using only contraction or tension in the agonist muscle. Static flexibility is measured in linear or angular terms.
  • Passive flexibility: Passive flexibility, sometimes called static-passive flexibility, is the ability to hold a stretch using body weight or some other external force.
  • Stretching: There are several types of stretching.
  • Dynamic stretching: Dynamic stretching consists of the controlled (usually slow) movements of a body segment to the limits of an individual's range of motion. Over the course of a set of repetitions, the individual may gradually increase the speed of movement, reach, or both. Examples of dynamic stretching include slow, controlled leg swings or arm swings.
  • Ballistic stretching: Characterized by fast actions and bouncing motions, ballistic stretching uses the momentum of the body in motion to stretch muscles beyond their resting points, as one might do by bouncing down repeatedly to touch one's toes. The effectiveness of ballistic stretching is reduced, because a quick return to the starting position does not allow the muscles involved to stay in position and "relax" at the limit of movement. In addition, repeated activation of the stretch reflex may strain or rupture tissue.
  • Static-active stretching: Static-active stretching (sometimes shortened to "active stretching") involves moving a body segment to a particular position and holding that position using only the agonist muscles of the body segment itself. Static-active stretching increases active flexibility; strengthens agonist muscles, which are being contracted; and relaxes antagonist muscles, which are being stretched. Raising one's leg high and holding it in position using only the leg muscles is an example of a static-active stretch.
  • Static-passive stretching: Static-passive, or "static," stretching is similar to static-active stretching, except that it incorporates an external force to hold the body segment at the end of its range of motion rather than using the agonist muscles alone. An example of static-passive stretching is bringing one's leg up high and holding it in position with one's hand.
  • Isometric stretching: In isometric stretching, muscles are subjected to forces through an isometric contraction. Isometric contractions cause no appreciable change in the length of muscles. In other words, despite force being applied, there is no movement. An example of isometric stretching is pushing or pulling against an immovable object. In response to the additional force applied during isometric stretching, additional muscle fibers that otherwise would have been at rest are stretched. Isometric stretching increases an individual's range of motion and helps develop strength in stretched positions.
  • Proprioceptive neuromuscular facilitation (PNF): PNF is a postisometric relaxation stretching technique. (Proprioception is a sense of self-awareness regarding body position and limb movement.) During PNF, a muscle group is passively stretched while contracting against resistance. Then the muscle group is passively stretched again through the newly expanded range of motion.
  • PNF relies on two neurophysiological mechanisms in addition to resistance and reflexes: irradiation and successive induction. Irradiation refers to the activation or use of nearby muscles or groups of muscles in synergy with the group that first responded to the trainer's force. This expansion of muscle activity beyond the prime muscle or target muscle group is one of the main principles behind PNF. Successive induction refers to contraction of an agonist muscle group followed by activation of the corresponding antagonist muscle group.
  • PNF requires the assistance of a trainer, therapist, or fellow athlete. After an individual moves a body segment into a stretched position, the trainer manipulates the body segment. When responding to the trainer's force, the individual activates both muscles and reflexes.

Technique

  • General: The American Academy of Sports Medicine (AASM) recommends that flexibility exercises should be part of an overall fitness program. Individuals should exercise in a manner and frequency that is sufficient to develop and maintain an optimum range of motion. Stretching exercises should stretch the major muscle groups and be performed a minimum of 2-3 days per week. Overall, for muscular strength, endurance, body composition, and flexibility, the AASM recommends that individuals perform one set of 8-10 exercises, with 8-12 repetitions of each exercise, 2-3 days per week.
  • Range of motion varies from individual to individual, depending on factors such as age, general physical fitness, present or past injuries, and amount of exposure to particular exercise routines, so stretching exercises can and should be tailored to the individual.
  • To measure range of motion, physical therapists and medical professionals usually use a double-armed goniometer. A goniometer is an instrument similar to a protractor, with a stationary arm held in position on the stationary body segment and a movable arm that is positioned on the movable body segment. After an individual has moved the body segment, a double-armed goniometer provides a reading of the angle achieved or distance moved.
  • Guidelines and precautions: The Department of Rehabilitation Services at Brigham and Women's Hospital in Massachusetts provides the following guidelines and precautions:
  • Since stretching is more effective if the intramuscular temperature is increased, individuals should warm up by using low-intensity exercises or applying heat before stretching.
  • Individuals should stretch the muscle beyond its usual range of motion, but not to the point of pain.
  • Caution should be observed by those with a history of steroid use, those with frail skin, and older individuals whose connective tissues may have lost their flexibility and who may have reduced capillary blood supplies.
  • The President's Council on Physical Fitness and Sports recommends static stretching or proprioceptive neuromuscular facilitation (PNF) stretching daily or at least three times a week, preferably after moderate or vigorous physical activity. (PNF is a postisometric relaxation stretching technique: a muscle group is passively stretched, contracts against resistance while in the stretched position, and then is passively stretched again through the expanded range of motion. Proprioception is a sense of self-awareness regarding body position and limb movement.) Each muscle group should be stretched 4-5 times, with each stretch held for 15-30 seconds.
  • The President's Council on Physical Fitness and Sports warns that stretching before physical activity (during the warm-up) may weaken muscles and decrease performance.
  • The Department of Rehabilitation Services at Brigham and Women's Hospital in Massachusetts describes three PNF techniques that incorporate the use of the stretch reflex, listed below.
  • Hold and relax: The body segment is moved by the assistant to the comfortable end of its range of motion, held for 6-10 seconds, and then moved back and held for 6-10 seconds at the other end of the range of motion.
  • Contract reflex: The body segment is moved by the assistant to the comfortable end of its range of motion and held for 6-10 seconds by the assistant while the individual tenses the muscle that is to be stretched against the assistant's resistance. Then the individual relaxes, and the assistant returns the body segment to the other end of the range of motion and holds for 6-10 seconds.
  • Slow reversal-hold relax: The body segment is moved by the assistant to the comfortable end of its range of motion and held for 6-10 seconds by the assistant while the individual tenses the agonist muscle against the assistant's resistance. Then the individual tenses the antagonist muscle against the assistant's resistance.
  • Stretch during warm-up: The Rehab Council of the American Chiropractic Association (ACA) says that flexibility exercises should be included in most warm-ups. The ACA cites the following benefits to be derived from a warm-up procedure, especially before a vigorous workout:
  • The rise in muscle temperature associated with warm-up exercises reduces the viscosity of cellular fluid in the muscles and thus enhances the mechanical efficiency of muscles. When muscle temperature is higher than body temperature, muscle contraction is more forceful and more rapid.
  • A higher body temperature increases the size of blood vessels, increasing the blood flow to muscle tissue and the delivery of nutrients.
  • The ACA identifies three types of warm-ups: A passive warm-up, such as a hot shower, will raise body temperature. A general, or nonspecific, warm-up might include simple calisthenics to move the major muscle groups. A specific warm-up will focus on the regions to be used during exercise.
  • Address the whole body: The National Institute on Aging describes stretching and flexibility exercises for hamstring muscles, calves, thigh, ankles, triceps, wrists, quadriceps, hips, upper body, chest, back, shoulders, and neck. As an example, instructions for stretching calves (lower leg muscles) are listed below.
  • Stance: The individual should stand with hands against a wall with the arms outstretched and elbows straight.
  • Move into stretch position: With the left knee slightly bent and the right foot turned slightly inward, the individual should step back a foot or two with the right leg, leaving the heel and foot flat on the floor. As the step back is taken, the individual should feel the calf muscles on the right leg stretch.
  • Hold in stretched position: The stretched position should be held for 10-30 seconds. Then the individual should bend the right knee, with the foot and heel still flat on the ground, and hold the new position for 10-30 seconds. The process is then repeated to stretch the calf muscles on the left leg.
  • Static stretching may be used for acute relief of muscle cramps and spasms. Most muscle movement is voluntary. A brief involuntary muscle contraction is called a spasm. A muscle cramp is an extended involuntary muscle contraction.
  • Although stretching often is used to relieve symptoms of delayed-onset muscle soreness (DOMS), recent studies show there is little or no effect of stretching on DOMS. (DOMS is soreness that occurs 12-48 hours after exercise, often occurring in the early days of an exercise program or after a significant change in an exercise program. DOMS usually dissipates on its own after 2-10 days.)

Theory/Evidence

  • General: Research suggests that static stretching increases short-term flexibility, or range of motion. Flexibility diminishes after about 15 minutes, but remains higher than at the base state. Early evidence suggests that flexibility gains are still observed 24 hours after stretching. Other research suggests that benefits diminish after only three minutes. Researchers have found that short-term flexibility gains may be sustained through ongoing training.
  • The Rehab Council of the American Chiropractic Association (ACA) reported on research demonstrating that proprioceptive neuromuscular facilitation (PNF) is more effective at increasing general range of motion than static stretching, because PNF combines aspects of passive stretching and isometric stretching.
  • Performance and injury-prevention benefits in doubt: A general consensus is lacking among researchers about the relationship between stretching and performance. Some studies show that dynamic stretching improves performance characteristics, such as agility, speed, and strength. On the other hand, other research shows that static stretching actually decreases performance. Therefore, the type of stretching an individual does may depend on whether the individual is interested in increasing flexibility or increasing performance aspects, such as power.
  • A general consensus is lacking among researchers on the relationship between stretching and injury prevention. Some research suggests a relationship, and some research suggests no such relationship. Researchers on the Faculty of Medicine and Health Sciences at Ghent University (Belgium) have stated that conclusive statements cannot be made about the relationship between stretching and injury prevention. But they have observed that sports with bouncing and jumping action such as soccer or football require muscle-tendon units that are compliant enough to release a high amount of energy. In such sports, stretching may reduce the risk of injury by reducing viscosity in the tendon and increasing compliance. If the muscle-tendon units are not complaint enough, the demands of the sport may exceed the capacity of the muscle-tendon units.
  • One researcher stated that stretching before strenuous exercise or competition does nothing to prevent overuse (and possible injury) of muscles during subsequent strenuous exercise or competition. In other words, overuse may cause injury, whether or not muscles are stretched before exertion.
  • Some muscles should be tight: Since muscles contribute to stability and stretching loosens them, not all muscle groups benefit from stretching. For example, overstretching the sacroiliac joints in the lower back may cause back pain from tightness in lower-back musculature. (Sacroiliac joints are structures that join the sacrum bone at the base of the spine with the ilium, part of the pelvic bone. There are two sacroiliac joints, left and right.) If stretching causes instability, the muscles may work to overcome the instability and may become tight, causing pain in the lower back. If additional muscles are recruited to compensate for the instability, pain may extend to the buttock, groin, or back of the thigh. In some cases, muscles may affect the sciatic nerve running down the back of the leg. Ironically, many individuals respond to such tightness by stretching still more, making the problem worse. In such cases where flexibility is undesirable, individuals who are very flexible may experience more problems with stretch-related sacroiliac instability than those with normal flexibility.
  • Some sports, such as jogging, swimming, and cycling, are characterized by low-intensity stretch-shortening cycles, which contract muscles to generate power. (A stretch-shortening cycle occurs when a contraction that lengthens a muscle is followed by a contraction that shortens the muscle.) Such sports rely more on the muscle-bone junction than the muscle-tendon unit to transfer power. Therefore, stretching to increase the compliance of the muscle-tendon unit may provide no benefit.
  • Some research suggests that less static flexibility may benefit some athletes, depending on the nature of the movement.
  • Special recommendation for swimmers: Swimmers frequently experience tightness of the pectoral (chest), latissimus dorsi (back), and sternocleidomastoid (neck) muscles. Tightness in these muscle groups may inhibit the middle and lower trapezius (upper back) muscles. An individual suffering from such muscle imbalance may rectify the situation with stretching exercises addressing the pectoral, latissimus dorsi, and sternocleidomastoid muscles.
  • Flexibility and age: According to the President's Council on Physical Fitness and Sports, static flexibility changes with age. Until they are grade-school age, children are highly flexible, because their bones have limited calcification and their joints are undeveloped. Static flexibility in children remains stable or decreases slightly until around age 12, then increases to its peak at around ages 15-18. Although research suggests decreased static flexibility and increased muscle stiffness through the adult years, the decreases in adult static flexibility with age are relatively small.
  • Avoid ballistic stretching: Some researchers believe that stretching, particularly ballistic stretching, is itself a cause of injuries. With ballistic stretching, the stretch reflex may rapidly increase tension. The increase in tension in turn increases the magnitude and rate of the stretch, possibly to the point of strain or muscle-tissue rupture.
  • Further study needed: The President's Council on Physical Fitness and Sports observes that the relationship between static flexibility and dynamic flexibility needs further study to learn whether static flexibility and dynamic flexibility are distinct or two aspects of the same flexibility component. Such study is being enabled by advances in muscle imaging techniques, such as magnetic resonance or ultrasound.
  • Measurements of dynamic flexibility tell how muscle tension increases at the limit of range of motion. They also show the relationship between elongation and rate of stretch on resulting force in stretching.
  • It seems clear that there is a relationship between dynamic flexibility and static flexibility, since some studies suggest that 44-66% of the variance of static flexibility may be accounted for by dynamic flexibility.
  • Stretch-sensitive sensors in muscle spindles work in concert with Gogli tendon organs, most of which are located in the junction between muscles and tendons. Gogli tendon organs are sensitive to the amount of force or tension generated within the muscle.

Safety

  • General: Stretching is generally a good thing when practiced appropriately. Individuals with injuries should meet with their healthcare providers or physical therapists to ensure that they are stretching appropriately and not exacerbating their condition.
  • Avoid ballistic stretching: Most medical practitioners, physical therapists, and sports-training specialists recommend against "ballistic" stretching, or using the weight and momentum of a body segment in a bouncing fashion to force an extension of range of motion.
  • Low force is most effective: First of all, research has suggested that low force over an extended period of time is most effective in permanently lengthening soft tissue, and the rapid pulses of high force involved in ballistic stretching are counter to that principle.
  • The pause at the end of the motion is important: Furthermore, repeated keying and rekeying of the stretch reflex without a pause at the end of the motion to give the agonist and antagonist muscles a chance to act against each other in their extended or contracted positions may strain or rupture tissue.
  • Harmful stretches:
  • Yoga plough: Intended to stretch the lower back, the yoga plough is accomplished by lying on one's back and raising the legs overhead and backward over the neck, while leaving the arms in their original position flat on the floor. According to the President's Council on Physical Fitness and Sports, the yoga plough forces the cervical vertebrae (top of the spine, including the neck) and thoracic vertebrae (middle spine) to bear an undue amount of body weight and places an extreme amount of bend in the neck. The President's Council on Physical Fitness and Sports says that healthy children may practice the yoga plough, but the pose would be problematic for those with arthritis or osteoporosis of the spine, and for amenorrheic women. (Amenorrhea is the absence of menstrual cycles. Malnutrition and excessive or extreme exercise are among the causes of amenorrhea.)
  • Hurdler's stretch: Another stretch that may be harmful is the hurdler's stretch. Depending on the direction that the body leans, the hurdler's stretch is intended to stretch the hamstrings (forward lean) or quadriceps (backward lean). (The hamstring is a set of three muscles in the back of the leg, above the knee. The quadriceps are a set of four muscles on the front of the leg, above the knee.)
  • How not to do the hurdler's stretch: The exercise is performed seated, with the leg to be stretched positioned straightforward. The traditional hurdler's stretch position is bending the other leg and positioning it underneath and behind the individual. The President's Council on Physical Fitness and Sports says that when the individual in such a position leans forward to stretch the hamstring, stress is placed on the medial (toward the center of the body, or "inside") structures of the bent leg. Also, because of the extreme rotation of the femur, the individual performing the hurdler's stretch for hamstring stretches may experience pain in the hip or groin. When leaning back to exercise the quadriceps in the classic position, the pelvis cannot rotate as the individual leans back, as this places stress on the lumbar spine (lower back). In addition, leaning back rotates the tibia in relation to the femur in a way that may damage the soft-tissue structures of the knee.
  • A better way: The exercise can be modified to reduce harm, though. Instead of bending the other leg and moving it behind, the individual can leave the leg forward, bend the knee, and move the foot so that it is adjacent to the knee on the straight leg. Then a forward or backward lean should stretch the hamstrings or quadriceps on the other leg safely.

Author Information

  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

References

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

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  3. Brigham & Women's Hospital. www.brighamandwomens.org
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  7. National Institutes of Health, National Institute on Aging. www.nia.nih.gov
  8. Natural Standard: The Authority on Integrative Medicine. www.naturalstandard.com
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