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No chapter abstract available.

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This chapter describes David Behm’s history as a Canadian football player who sought to reach the professional level. However, he lacked the essential running speed of a professional football running back. Based on the literature from the 1970s, he trained his flexibility aggressively, in order to increase his running speed (improve sprint performance by increasing stride length and decreasing resistance to limb movement), and decrease injuries. His extensive flexibility training did not seem to positively impact either variable. Was the research or common knowledge about stretching and flexibility incorrect?

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Whereas animals have pandiculated (stretch and yawn) for eons, our historical records indicate that humans have stretched for thousands of years (Yoga (~3000 BCE), Asian martial arts (~1000 BCE), Greeks and Egyptians (~2000 BCE). While ballistic stretching was popular in the 1950s, static stretching became predominant from the 1960s to the late 1990s. Proprioceptive neuromuscular facilitation stretching was popularized to a greater degree starting in the 1970s. However, in the late 1990s research started to indicate that static stretching could lead to performance impairments. Since that time dynamic stretching has made a resurgence. The most recent studies suggest that the move away from static stretching may have been premature and based on impractical study designs.

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Flexibility is defined as the range of motion around a joint and can be altered with passive and active static, dynamic and proprioceptive neuromuscular facilitation (PNF) stretching as well as other techniques. These stretching techniques can provide elastic (acute) or plastic (semi-permanent) changes to joint flexibility. The majority of studies show that static and PNF stretching provide greater increases in range of motion (ROM) compared to dynamic stretching. Normative data for joint ROM use measurement techniques such as the use of goniometers, fleximeters, inclinometers, photography, sit (stand) and reach tests display high reliability but may not provide similar between device values. Females tend to have greater joint ROM than men due to anatomical differences, less tissue stiffness and endocrine differences. Inactivity plays a very substantial contributing role in the decrease in flexibility that is recorded with ageing (also related to increased collagen proportions and protein cross-linkages), Youth tend to have higher flexibility levels, but the lower levels of flexibility with puberty compared to childhood can also be related to inactivity. Regarding the effect of genetics on flexibility, activity again plays a more important role than DNA as studies have shown weak to strong correlations.

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Increased flexibility can be achieved by increasing tissue temperatures (thixotropic effects), which decrease tissue visco-elasticity. Static and proprioceptive neuromuscular facilitation (PNF) stretching can activate a number of inhibitory reflexes or disfacilitate spindle reflexes. (discharge frequency of nuclear chain and nuclear bag fibres). Golgi tendon organs and Renshaw cells do not play a substantial inhibitory role with static stretching. However, extensive static stretching can activate cutaneous afferent inhibition, while PNF stretching, which involve the contraction of the antagonist muscle could facilitate reciprocal inhibition. Dynamic stretching tends to excite rather than inhibit these reflexes. The stretch tolerance theory can also help explain increased range of motion (ROM) as the individual accommodates the discomfort or pain associated with stretching and can push themselves past their prior ROM. Skeletal configuration, alignment and ligaments are resistant to elongation by stretching except with the intense flexibility training routines by gymnasts, dancers, figure skaters and others. Excessive fat can impede joint ROM, whereas excessive elongation of nerves (>20 percent) can lead to injury. Very hypertrophied muscle can also provide some ROM restrictions, however the great extensibility of muscle puts into dispute the old theory of muscle boundness. Myofibrils can elongate double their resting length mainly due to the protein titin. Muscle is more compliant than tendons, with tendons accounting for less than half of the musculotendinous unit change. Muscle extensibility can also be altered by changes in fascicle angle (trivial), fascicle rotation (minor) and fascicle elongation (substantial). However, stretch tolerance may provide a greater impetus to enhanced ROM than decreased musculotendinous stiffness.

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Static and proprioceptive neuromuscular facilitation stretching tend to provide greater flexibility than dynamic stretching. Flexibility training adaptations can persist for 3–8 weeks with either reduced (once a week) or minimal stretching and activity. This persistent flexibility adaptations may be partially ascribed to neural adaptations such as an intrinsic disfacilitation of spindle afferent discharge. There is evidence with human flexibility training for alterations in muscle pennation angles, visco-elastic properties and stretch tolerance.

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While stretching a specific muscle will increase its range of motion (ROM), there can also be ROM increases in other muscles that have not been stretched. The earlier research on crossover or non-local muscle fatigue, which demonstrated that unilaterally fatiguing one muscle could lead to impairments in homologous (same muscle: crossover fatigue) or heterologous (different muscle: non-local muscle fatigue) muscles was applied to stretching with similar results. Stretching one muscle group can increase the ROM of other non-stretched muscles and joints whether it is a single session (acute) or with chronic stretch training. As prolonged stretching before an activity can induce performance deficits in the stretched muscles, research examined possible global (crossover and non-local) effects and indeed discovered small magnitude decrements in non-stretched muscles. The increased global ROM may be attributed to increases in stretch (pain) tolerance, downregulation of sympathetic nerve stimulation, decreased reflex activity or greater compliance of myofascial chains.

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Optimal improvements in flexibility are typically achieved with 30–60 seconds of static stretching. While it is not necessary to perform stretching at the point of discomfort stretching at 60–85 percent of maximal intensity provides the greatest benefits. Stretching in the middle or later in the day should enhance range of motion because the body is warmer (decreased visco-elasticity). It is not recommended to stretch your back early in the morning. Although, stretching can be performed every day, increases in flexibility are also experienced when stretching two or 3–6 days per week. Whereas pre-event prolonged static stretching is not recommended, owing to the possibility of performance impairments, short to moderate duration static stretching (<60 seconds per muscle group) within a full warm-up including dynamic stretching and dynamic activity does not impair performance. Post-activity stretching should be lower intensity since the tissues are fatigued and susceptible to injury if subjected to intense elongation. Post-activity stretching, can also increase psychological feelings of relaxation. When stretching, breathing patterns should be at a slow and controlled rate to promote greater relaxation.

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While, stretching programmes do not reduce the incidence of all cause injuries. They can reduce the incidence of musculotendinous and ligamentous injuries especially with more powerful actions such as sprinting and change of direction (agility). As slips or falls may be too rapid to be compensated by reflexes, increased flexibility may increase the energy absorbing capability of the musculotendinous unit. Flexibility-induced improvements with hip/pelvic orientation can positively affect spinal curves decreasing low back pain. Similarly, stretching may decrease the discomfort of dysmenorrhea, the recovery of an immobilized limb or the flexibility of a contralateral homologous or heterologous muscle. While enhanced flexibility is correlated with decreased arterial stiffness and stretching can increase blood flow to the stretched muscle, individuals with cardiovascular diseases must be cautious, owing to stretch-induced increases in the rate pressure product.

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It was commonly believed that static stretching would enhance subsequent performance by allowing a greater range of motion with less resistance to movement. However, the relatively recent findings that prolonged static and proprioceptive neuromuscular facilitation (PNF) stretching induced performance impairments changed the emphasis within warm-ups to dynamic stretching. The inclusion of static stretching within a warm-up should depend upon the type or demands of the activity, the level of the athlete and the priority of reducing the incidence of musculotendinous injuries. Prolonged static stretching without a full warm-up can impair performance in both trained and untrained individuals, young and old, whether the stretch is performed at a moderate or high intensity. However, studies incorporating static and PNF stretching within a full warm-up do not typically report performance decrements. Dynamic stretching, is reported to either induce no significant impairments or provide small performance improvements. Adding dynamic to static stretching tends to counterbalance possible impairments associated with prolonged static stretching in isolation. Individuals should incorporate at least 90 seconds of dynamic stretching per muscle group within a full warm-up. The full warm-up should include a 5–15-minute submaximal aerobic component, less than 60 seconds of static stretching per muscle group, more than 90 seconds of dynamic stretching per muscle group and finish with dynamic activity that should be activity or sport specific.

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In contrast with the reported detrimental effects of an acute session of prolonged static stretching, there are many physiological adaptations with chronic static stretch training that should enhance performance. However, the evidence from static stretch training studies is contradictory. The few dynamic stretch studies do show performance improvements but not with every measure. A recent review of chronic stretching effects on jump and sprint performance demonstrated a significant but trivial magnitude increase in jump height but no significant effect on sprint time or speed. Based on the few and diverse studies with small weekly training volumes or lack of intensity, static stretching training programmes in these studies was not a sufficient stimulus to substantially enhance jump and sprint performance. More studies are necessary with more robust training programmes.

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While stretching has been universally accepted as an effective means for improving range of motion, recent research documents that static stretching may also be able to increase muscle strength and hypertrophy in humans. This research arose from prior animal studies that used stretching durations that ranged from 30 minutes per day for five weeks to chronic interventions of 24 hours per day, seven days per week for up to six weeks consistently showed large muscle mass increases in the stretched muscle. Even without an active contraction as used with resistance training, passive static stretching places tension on the muscle which seems to trigger increased protein synthesis promoting strength and hypertrophy improvements. There is also the possibility that stretch-induced restrictions in blood flow help to enhance muscle hypertrophy. Recent systematic reviews report significant, small magnitude improvements in maximal strength and muscle size with static stretching, if performed with sufficient volume, intensity, and frequency. While resistance training would be more efficient, enhancing muscle strength and hypertrophy may be promising for individuals with restricted accessibility to training equipment, after serious injuries that cause limb immobilization, for whom active resistance training might be contraindicated or unmotivated individuals (e.g., people who do not like higher intensity activity).

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No chapter abstract available.

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Traditionally, resistance training was thought to lead to muscle boundness, which slow the athlete and reduce their flexibility. However, the research demonstrates the opposite effect. All types of strength training, except for calisthenics (body mass exercises such as push-ups) can increase range of motion (ROM). Resistance training actions are similar to dynamic stretching, albeit with an additional external load. Sedentary individuals have exhibited greater improvements in ROM with resistance training compared to their active counterparts, probably owing to their lower baseline level of flexibility, which allows for a greater magnitude of training-induced ROM enhancements. A recent meta-analysis reported that factors such as training frequency, training duration, stretched joint, age, and sex do not significantly influence the ROM outcomes with resistance training. The underlying mechanisms for resistance training-induced increases in ROM are believed to be similar to stretching (e.g., increased stretch/pain tolerance, increased fascicle length and changes in pennation angle).

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Massage has been used for millennia as a relaxation technique that could improve range of motion. Foam rolling is a recent popular development. An acute session of foam rolling can increase the range of motion (ROM) immediately after the exercise and this increase can last for more than 60 minutes post-exercise, with a trend towards small magnitude enhanced sprint performance but minimal effects on jumping or strength performance. Chronic foam rolling training can provide large magnitude increases in ROM over time, especially when performed for more than four weeks and focused on the quadriceps and hamstrings. Foam rolling training does not result in significant performance changes. The underlying mechanisms for improving ROM are suggested to be thixotropic (decreased visco-elasticity), reflex-induced decreases in sympathetic activity leading to greater relaxation, and the ubiquitous increases in pain tolerance. It is recommended to perform multiple sets of 30–60 seconds of rolling, which can be performed below the maximum pain tolerance (50–90 percent of maximum pain tolerance).

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The use of devices to induce local (on one muscle) vibration is another recent popular development to increase range of motion and enhance performance. An acute session of percussive massage devices can be effective for increasing range of motion with a lack of improvements in strength, balance, acceleration, agility, and explosive activities. The common mechanisms of increased pain tolerance, thixotropic effects (decreased visco-elasticity), and an attenuation of spinal reflexes.

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Instrument Assisted Soft Tissue Mobilization (IASTM) is similar to manual massage or foam rolling as it involves placing stress and strain on the tissues using metal tools that conform to specific body areas and permit individuals to apply pressure. A number of studies have revealed improved range of motion (ROM) with a single session (acute) of IASTM at the neck (cervical), shoulder internal rotation and horizontal adduction, hamstrings (hip flexion), knee, and hip, as well as ankle dorsiflexion following IASTM treatment durations of as little as two and five minutes. The improvements have been reported to last for 45 minutes after treatment, with one study reporting significant ROM gains 24 hours after IASTM treatment. Training studies of 3–6 weeks duration have also reported ROM improvements. There are no reports of subsequent performance decrements with IASTM, with some reports of performance enhancements when IASTM is conducted alone or in combination with other treatments such as foam rolling or flossing. Increased pain tolerance, and myofascial chains are hypothesized to be possible mechanisms.

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Floss bands are applied before or after activity. A single floss band treatment provides small to moderate magnitude increases in range of motion (ROM), with weak evidence that flossing during a warm-up may provide greater ROM improvements than stretching, but no superior effect when compared to foam rolling. Regarding performance effects, flossing can provide small to moderate magnitude improvements in jumping and strength performance. Floss bands are typically applied tight enough to restrict blood flow. Mechanisms underlying flossing are reported to be reperfusion, fascial shearing, and blood occlusion. The floss-induced ischemia (from occlusion) and subsequent blood flow reperfusion (hyperemia) following its removal may enhance metabolic activity and elevate growth hormone and catecholamine levels and also increase the pain threshold.

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This chapter provides photographs with explanations of a variety of stretching exercises that can be employed within a standard athletic warm-up or within a dedicated flexibility training sessions. A standardized warm-up is presented below which outlines in general the allocation of flexibility, mobility and activation activities.