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As with other forms of therapeutic exercise, such as strengthening exercises and endurance training, there are a number of essential elements that determine the effectiveness and outcomes of stretching interventions. The determinants (parameters) of stretching, all of which are interrelated, include alignment and stabilization of the body during stretching; the intensity (magnitude), duration, speed, frequency, and mode (type) of stretch; and the integration of neuromuscular inhibition or facilitation and functional activities into stretching programs. By manipulating the determinants of stretching interventions, which are defined in Box 4.3, a therapist has many options from which to choose when designing stretching programs that are safe and effective and meet the needs, functional goals, and capabilities of many patients. Each of these determinants is discussed in this section of the chapter.
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BOX 4.3 Determinants of Stretching Interventions
Alignment: Positioning a limb or the body such that the stretch force is directed to the appropriate muscle group.
Stabilization: Fixation of one site of attachment of the muscle as the stretch force is applied to the other bony attachment.
Intensity of stretch: Magnitude of the stretch force applied.
Duration of stretch: Length of time the stretch force is applied during a stretch cycle.
Speed of stretch: Speed of initial application of the stretch force.
Frequency of stretch: Number of stretching sessions per day or per week.
Mode of stretch: Form or manner in which the stretch force is applied (static, ballistic, cyclic); degree of patient participation (passive, assisted, active); or the source of the stretch force (manual, mechanical, self).
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Many of the investigations comparing the type, intensity, duration, and frequency of stretching have been carried out with healthy, young adults as subjects. The findings and recommendations of these studies are difficult to generalize and apply to patients with long-standing contractures or other forms of tissue restriction. Therefore, many decisions, particularly those related to the type, intensity, duration, and frequency of stretching, must continue to be based on a balance of scientific evidence and sound clinical judgments by the therapist.
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There are four broad categories of stretching exercises: static stretching, cyclic (intermittent) stretching, ballistic stretching, and stretching techniques based on the principles of PNF.39,48,74,173 Each of these forms of stretching are effective in elongating muscle and increasing ROM. Each can be carried out in various manners—that is, manually or mechanically, passively or actively, and by a therapist or independently by a patient—giving rise to many terms that are used in the literature to describe stretching interventions. The stretching interventions listed in Box 4.4 are defined and discussed in this section.
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BOX 4.4 Types of Stretching
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Alignment and Stabilization
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Just as appropriate alignment and effective stabilization are fundamental components of muscle testing and goniometry as well as ROM and strengthening exercises, they are also essential elements of effective stretching.
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Proper alignment or positioning of the patient and the specific muscles and joints to be stretched is necessary for patient comfort and stability during stretching. Alignment influences the amount of tension present in soft tissue and consequently affects the ROM available in joints. Alignment of the muscles and joint to be stretched as well as the alignment of the trunk and adjacent joints must all be considered. For example, to effectively stretch the rectus femoris (a muscle that crosses two joints), the lumbar spine and pelvis should be maintained in a neutral position as the knee is flexed and the hip extended. The pelvis should not tilt anteriorly nor should the low back hyperextend; the hip should not abduct or remain flexed (Fig. 4.8 A and B). When a patient is self-stretching to increase shoulder flexion, the trunk should be erect, not slumped (Fig. 4.9 A and B).
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NOTE: Throughout this and later chapters, recommendations for appropriate alignment and positioning during stretching procedures are identified. If it is not possible for a patient to be placed in or assume the recommended postures because of discomfort, restrictions of motion of adjacent joints, inadequate neuromuscular control, or insufficient cardiopulmonary capacity, the therapist must critically analyze the situation to determine an alternative position.
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To achieve an effective stretch of a specific muscle or muscle group and associated periarticular structures, it is imperative to stabilize (fixate) either the proximal or distal attachment site of the muscle-tendon unit being elongated. Either site may be stabilized, but for manual stretching, it is common for a therapist to stabilize the proximal attachment and move the distal segment, as shown in Figure 4.10 A.
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For self-stretching procedures, a stationary object, such as a chair or a doorframe, or active muscle contractions by the patient may provide stabilization of one segment as the other segment moves. During self-stretching, it is often the distal attachment that is stabilized as the proximal segment moves (Fig. 4.10 B).
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Stabilization of multiple segments of a patient's body also helps maintain the proper alignment necessary for an effective stretch. For example, when stretching the iliopsoas, the pelvis and lumbar spine must maintain a neutral position as the hip is extended to avoid stress to the low back region. Sources of stabilization include manual contacts, body weight, or a firm surface, such as a table, wall, or floor.
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The intensity (magnitude) of a stretch force is determined by the load placed on soft tissue to elongate it. There is general agreement among clinicians and researchers that stretching should be applied at a low-intensity by means of a low-load.1,11,13,30,48,74,99,103 Low-intensity stretching in comparison to high-intensity stretching makes the stretching maneuver more comfortable for the patient and minimizes voluntary or involuntary muscle guarding, so a patient can either remain relaxed or assist with the stretching maneuver.
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Low-intensity stretching (coupled with a long-duration of stretch) results in optimal rates of improvement in ROM without exposing tissues, possibly weakened by immobilization, to excessive loads and potential injury.99,103 Low-intensity stretching has also been shown to elongate dense connective tissue, a significant component of chronic contractures, more effectively and with less soft tissue damage and postexercise soreness than a high-intensity stretch.3
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One of the most important decisions a therapist must make when selecting and implementing a stretching intervention (stretching exercises or use of a mechanical stretching device) is to determine the duration of stretch that is expected to be safe, effective, practical, and efficient for each situation.
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The duration of stretch refers to the period of time a stretch force is applied and shortened tissues are held in a lengthened position. Duration most often refers to how long a single cycle of stretch is applied. If more than one repetition of stretch (stretch cycle) is carried out during a treatment session (which is most often the case), the cumulative time of all the stretch cycles reflects the total duration of stretch, also referred to as the total elongation time.
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In general, the shorter the duration of a single stretch cycle, the greater the number of repetitions applied during a stretching session. Many combinations have been studied.
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FOCUS ON EVIDENCE
In a study by Cipriani and associates,27 two repetitions of 30-second hamstring stretches were found to be equally effective as six repetitions of 10-second stretches. However, Roberts and Wilson130 found that over the course of a 5-week period and equal total duration times, three 15-second hamstring stretches each day yielded significantly greater stretch-induced gains in ROM than nine daily 5-second stretches.
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Despite many studies over several decades, there continues to be a lack of agreement on the "ideal" combination of the duration of a single stretch cycle and the number of repetitions of stretch that should be applied in a daily stretching program to achieve the greatest and most sustained stretch-induced gains in ROM or reduction of muscle stiffness. The duration of stretch must be put in context with other stretching parameters, including intensity, frequency, and mode of stretch. Key findings from a number of studies are summarized in Box 4.5.
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BOX 4.5 Intensity, Duration, Frequency, and Mode of Stretch—Evidence-Based Interrelationships and Impact on Stretching Outcomes
There is an inverse relationship between intensity and duration as well as between intensity and frequency of stretch.
The lower the intensity of stretch, the longer the time the patient will tolerate stretching and the soft tissues can be held in a lengthened position.
The higher the intensity, the less frequently the stretching intervention can be applied to allow time for tissue healing and resolution of residual muscle soreness.
A low-load (low-intensity), long-duration stretch is considered the safest form of stretch and yields the most significant, elastic deformation and long-term, plastic changes in soft tissues.
Manual stretching and self-stretching in hypomobile but healthy subjects6,7,8,14,27,54 and prolonged mechanical stretching in patients with chronic contractures16,77,80,99,111 yield significant stretch-induced gains in ROM.
In the well elderly, stretch cycles of 15, 30, and 60 seconds applied to the hamstrings for four repetitions have all been shown to produce significant gains in ROM with the greatest and longest-lasting improvements occurring with the use of repeated 60-second stretch cycles.54
In healthy young and/or middle-age adults:
Stretch durations of 15, 30, 45, or 60 seconds or 2 minutes to lower extremity musculature produced significant gains in ROM.6,7,27,44,104,166
Stretch cycles of 30- and 60-second durations applied to the hamstrings for one repetition daily are both more effective for increasing ROM than one repetition daily of a 15-second stretch cycle but are equally effective when compared to each other.6
Two repetitions daily of a 30-second static stretch of the hamstrings yield significant gains in hamstring flexibility similar to those seen with six repetitions of 10-second static stretches daily.27
Static stretches of the hip adductors for 15 seconds or 2 minutes produce equal improvements in ROM.104
There seems to be no additional benefit to holding each stretch cycle beyond 60 seconds.7,89
Three cycles of 30-second and 1-minute stretches are no more effective for improving ROM than one cycle of each duration of stretch.7
Longer total durations of passive stretch yield longer-lasting decreases in muscle-tendon stiffness than short-duration stretches.57,106,133
When the total duration of stretch (total elongation time) is equal, cyclic stretching is equally effective and possibly more comfortable than static stretching.143
For patients with chronic, fibrotic contractures:
Common durations of manual stretching or self-stretching (several repetitions of 15-second or 30-second stretches) may not be effective.99,116
Use of prolonged static stretch with splints or casts is more effective.16,80,99,111
Frequency of stretching needs to occur a minimum of two times per week63 for healthy hypomobile individuals, but more frequent stretching is necessary for patients with soft tissue pathology to achieve gains in ROM.
Although stretch-induced gains in ROM often persist for several weeks to a month in healthy adults after cessation of a stretching program, permanent improvement in mobility can be achieved only by use of the newly gained ROM in functional activities and/or with a maintenance stretching program.166
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Several descriptors are used to differentiate between a long-duration versus a short-duration stretch. Terms such as static, sustained, maintained, and prolonged are all used to describe a long-duration stretch, whereas terms such as cyclic, intermittent, or ballistic are used to characterize a short-duration stretch. There is no specific time period assigned to any of these descriptors, nor is there a time frame that distinguishes a long-duration from a short-duration stretch.
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Static stretching* is a commonly used method of stretching in which soft tissues are elongated just past the point of tissue resistance and then held in the lengthened position with a sustained stretch force over a period of time. Other terms used interchangeably are sustained, maintained, or prolonged stretching. The duration of static stretch is predetermined prior to stretching or is based on the patient's tolerance and response during the stretching procedure.
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In research studies, the term "static stretching" has been linked to durations of a single stretch cycle ranging from as few as 5 seconds to 5 minutes per repetition when either a manual stretch or self-stretching procedure is employed. † If a mechanical device provides the static stretch, the time frame can range from almost an hour to several days or weeks.17,77,80,99,103,110 (See additional information on mechanical stretching later in this section.)
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FOCUS ON EVIDENCE
In a systematic review of the literature (28 studies) on hamstring stretching,39 a 30-second manual or self-stretching procedure performed for one or more repetitions was the most frequently used duration per repetition of stretch in static stretching programs. A 30-second stretch per repetition also has been identified as the median duration of stretch in a review of the literature of studies on calf muscle stretching.171
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Static stretching is well accepted as an effective form of stretching to increase flexibility and ROM1,39,74,75,93,118,133,162 and has been considered a safer form of stretching than ballistic stretching for decades.43 Early research established that tension created in muscle during static stretching is approximately half that created during ballistic stretching.159 This is consistent with our current understanding of the viscoelastic properties of connective tissue, which lies in and around muscles, as well as the neurophysiological properties of the contractile elements of muscle.
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As discussed in the previous section of this chapter, non-contractile soft tissues are known to yield to a low-intensity, continuously applied stretch force, as used in static stretching. Furthermore, a low-intensity, slowly applied, continuous, end-range static stretch does not appear to cause significant neuromuscular activation (evidence of increased EMG activity) of the stretched muscle.24,108 However, the assertion that static stretching contributes to neuromuscular relaxation (inhibition) of the stretched muscle, as the result of activation of the GTO, is not supported by experimental evidence in human research studies.24,98,138
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Static Progressive Stretching
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Static progressive stretching is a term that characterizes how static stretching is applied for maximum effectiveness. The shortened soft tissues are held in a comfortably lengthened position until a degree of relaxation is felt by the patient or therapist. Then the shortened tissues are incrementally lengthened even further and again held in the new end-range position for an additional duration of time.17,80 This approach involves continuous displacement of a limb by varying the stretch force (stretch load) to capitalize on the stress-relaxation properties of soft tissue111 (see Fig. 4.7 B).
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Most studies that have explored the merits of static progressive stretching have examined the effectiveness of a dynamic orthosis (see Fig. 4.13), which allows the patient to control the degree of displacement of the limb.17,80 Manual stretching and self-stretching procedures are also routinely applied in this manner.
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Cyclic (Intermittent) Stretching
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A relatively short-duration stretch force that is repeatedly but gradually applied, released, and then reapplied is described as a cyclic (intermittent) stretch.14,52,112,143 Cyclic stretching, by its very nature, is applied for multiple repetitions (stretch cycles) during a single treatment session. With cyclic stretching, the end-range stretch force is applied at a slow velocity, in a controlled manner, and at relatively low-intensity. For these reasons, cyclic stretching is not synonymous with ballistic stretching, which is characterized by high-velocity movements.
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The differentiation between cyclic stretching and static stretching based on the duration that each stretch is applied is not clearly defined in the literature. According to some authors, in cyclic stretching, each cycle of stretch is held between 5 and 10 seconds.52,143 However, investigators in other studies refer to stretching that involves 5- and 10-second stretch cycles as static stretching.27,130 There is also no consensus on the optimal number of repetitions of cyclic stretching during a treatment session. Rather, this determination is often based on the patient's response to stretching.
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Based on clinical experience, some therapists hold the opinion that appropriately applied, end-range cyclic stretching is as effective but more comfortable for a patient than a static stretch of comparable intensity, particularly if the static stretch is applied continuously for more than 30 seconds. There is some evidence to support this opinion. Although there have been few studies on cyclic or intermittent stretching (aside from those on ballistic stretching), cyclic loading has been shown to increase flexibility as effectively or more effectively than static stretching.112,143
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FOCUS ON EVIDENCE
In a study of nonimpaired young adults, 60 seconds of cyclic stretching of calf muscles caused tissues to yield at slightly lower loads than one 60-second, two 30-second, or four 15-second static stretches, possibly due to decreased muscle stiffness.112 In another study that compared cyclic and a prolonged static stretch,143 the authors speculated that heat production might occur because of the movement inherent in cyclic stretching and cause soft tissues to yield more readily to stretch. The authors of the latter study also concluded that cyclic stretching was more comfortable than a prolonged static stretch.
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Importance of a Slowly Applied Stretch
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To minimize muscle activation during stretching and reduce the risk of injury to tissues and poststretch muscle soreness, the speed of stretch should be slow.60,63,135 The stretch force should be applied and released gradually. A slowly applied stretch is less likely to increase tensile stresses on connective tissues98,106,107 or to activate the stretch reflex. Remember, the Ia fibers of the muscle spindle are sensitive to the velocity of muscle lengthening. A slow rate stretch also affects the viscoelastic properties of connective tissue, making them more compliant. In addition, a stretch force applied at a low-velocity is easier for the therapist or patient to control and is, therefore, safer than a high-velocity stretch.
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A rapid, forceful intermittent stretch—that is, a high-speed and high-intensity stretch—is commonly called ballistic stretching.1,7,8,48,135,173 It is characterized by the use of quick, bouncing movements that create momentum to carry the body segment through the ROM to stretch shortened structures. Although both static stretching and ballistic stretching have been shown to improve flexibility equally, ballistic stretching is thought to cause greater trauma to stretched tissues and greater residual muscle soreness than static stretching.163
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Consequently, although ballistic stretching has been shown to increase ROM safely in young, healthy subjects participating in a conditioning program,71 it is, for the most part, not recommended for elderly or sedentary individuals or patients with musculoskeletal pathology or chronic contractures. The rationale for this recommendation is35:
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Tissues, weakened by immobilization or disuse, are easily injured.
Dense connective tissue found in chronic contractures does not yield easily with high-intensity, short-duration stretch; rather, it becomes more brittle and tears more readily.
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High-Velocity Stretching in Conditioning Programs and Advanced-Phase Rehabilitation
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Although controversial, there are situations in which high-velocity stretching is appropriate for carefully selected individuals. For example, a highly trained athlete involved in a sport, such as gymnastics, that requires significant dynamic flexibility may need to incorporate high-velocity stretching in a conditioning program. Also, a young, active patient in the final phase of rehabilitation, who wishes to return to high-demand recreational or sport activities after a musculoskeletal injury, may need to perform carefully progressed, high-velocity stretching activities prior to beginning plyometric training or simulated, sport-specific exercises or drills.
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If high-velocity stretching is employed, rapid, but low-load (low-intensity) stretches are recommended, paying close attention to effective stabilization. The following self-stretching progression is designed as a transition from static stretching to ballistic stretching to improve dynamic flexibility.173
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Static stretching → Slow, short end-range stretching → Slow, full-range stretching → Fast, short end-range stretching → Fast, full-range stretching.
The stretch force is initiated by having the individual actively contract the muscle group opposite the muscle and connective tissues to be stretched.
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Frequency of stretching refers to the number of bouts (sessions) per day or per week a patient carries out a stretching regimen. The recommended frequency of stretching is based on the underlying cause of impaired mobility, the quality and level of healing of tissues, the chronicity and severity of a contracture, as well as a patient's age, use of corticosteroids, and previous response to stretching. Because few studies have attempted to determine the optimal frequency of stretching within a day or a week, it is not possible to draw evidence-based guidelines from the literature. As with decisions on the most appropriate number of repetitions of stretch in an exercise session, most suggestions are based on opinion. Frequency on a weekly basis ranges from two to five sessions, allowing time for rest between sessions for tissue healing and to minimize postexercise soreness. Ultimately, the decision is based on the clinical discretion of the therapist and the response and needs of the patient.
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A therapist must be aware of any breakdown of tissues with repetitive stretch. A fine balance between collagen tissue breakdown and repair is needed to allow an increase in soft tissue lengthening. If there is excessive frequency of loading, tissue breakdown exceeds repair. Ultimately tissue failure is a possibility. In addition, if there is progressive loss of ROM over time rather than a gain in range, continued low-grade inflammation from repetitive stress can cause excessive collagen formation and hypertrophic scarring.
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The mode of stretch refers to the form of stretch or the manner in which stretching exercises are carried out. Mode of stretch can be defined by whom or what is applying the stretch force or whether the patient is actively participating in the stretching maneuver. Categories include, but are not limited to, manual and mechanical stretching or self-stretching as well as passive, assisted, or active stretching. Regardless of the form of stretching selected and implemented, it is imperative that the shortened muscle remains relaxed and that the restricted connective tissues yield as easily as possible to the stretch. To accomplish this, stretching procedures should be preceded by either low-intensity active exercise or therapeutic heat to warm up the tissues that are to be lengthened.
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There is no best form or type of stretching. What is important is that the therapist and patient have many modes of stretching from which to choose. Box 4.6 lists some questions a therapist needs to answer to determine which forms of stretching are most appropriate and most effective for each patient at different stages of a rehabilitation program.
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BOX 4.6 Considerations for Selecting Methods of Stretching
Based on the results of your examination, what tissues are involved and impairing mobility?
Is there evidence of pain or inflammation?
How long has the hypomobility existed?
What is the stage of healing of restricted tissues?
What form(s) of stretching have been implemented previously? How did the patient respond?
Are there any underlying diseases, disorders, or deformities that might affect the choice of stretching procedures?
Does the patient have the ability to actively participate in, assist with, or independently perform the exercises? Consider the patient's physical capabilities, age, ability to cooperate, or ability to follow and remember instructions.
Is assistance from a therapist or caregiver necessary to execute the stretching procedures and appropriate stabilization? If so, what is the size and strength of the therapist or the caregiver who is assisting the patient with a stretching program?
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Characteristics. During manual stretching, a therapist or other trained practitioner or caregiver applies an external force to move the involved body segment slightly beyond the point of tissue resistance and available ROM. The therapist manually controls the site of stabilization as well as the direction, speed, intensity, and duration of stretch. As with ROM exercises (described in Chapter 3), manual stretching can be performed passively, with assistance from the patient, or even independently by the patient.
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Manual stretching typically employs a controlled, end-range, static, progressive stretch applied at an intensity consistent with the patient's comfort level. It is held for 15 to 60 seconds and repeated for at least several repetitions.
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CLINICAL TIP
Remember—stretching and ROM exercises are not synonymous terms. Stretching takes soft tissue structures beyond their available length to increase ROM. ROM exercises stay within the limits of tissue extensibility to maintain the available length of tissues.
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Effectiveness. Despite widespread use of manual stretching in the clinical setting, its effectiveness for increasing the extensibility of range-limiting muscle-tendon units is debatable. Although some investigators 44 have found that manual stretching increases muscle length and ROM in nonimpaired subjects, the short-duration of stretch that typically occurs with manual stretching may be why other investigators have reported a negligible effect from a manual stretching program,66 especially in the presence of long-standing contractures associated with tissue pathology.99
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Application. The following are points to consider about the use of manual stretching.
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Manual stretching may be most appropriate in the early stages of a stretching program when a therapist wants to determine how a patient responds to varying intensities or durations of stretch and when optimal stabilization is most critical.
Manual stretching performed passively is an appropriate choice for a therapist or caregiver if a patient cannot perform self-stretching owing to a lack of neuromuscular control of the body segment to be stretched.
If a patient has control of the body segment to be stretched, it is often helpful to ask the patient to assist the therapist with the manual stretching maneuver, particularly if the patient is apprehensive about moving and is having difficulty relaxing. For example, if the patient concentrically contracts the muscle opposite the short muscle and assists with joint movement, the range-limiting muscle tends to relax reflexively, thus decreasing muscle tension interfering with elongation. This is one of several stretching procedures based on proprioceptive neuromuscular facilitation techniques that are discussed later in this chapter.
Using procedures and hand placements similar to those described for self-ROM exercises (see Chapter 3), a patient can also independently lengthen range-limiting muscles and periarticular tissues with manual stretching. As such, this form of stretching is usually referred to as self-stretching and is discussed in more detail as the next topic in this section.
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NOTE: Specific guidelines for the application of manual stretching, as well as descriptions and illustrations of manual stretching techniques for the extremities (Figures 4.16 through 4.36), are presented in later sections of this chapter.
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Characteristics. Self-stretching (also referred to as flexibility exercises or active stretching) is a type of stretching procedure a patient carries out independently after careful instruction and supervised practice. Self-stretching enables a patient to maintain or increase the ROM gained as the result of direct intervention by a therapist. This form of stretching is often an integral component of a home exercise program and is necessary for long-term self-management of many musculoskeletal and neuromuscular disorders.
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Effectiveness. Teaching a patient to carry out self-stretching procedures correctly and safely is fundamental for preventing re-injury or future dysfunction. Proper alignment of the body or body segments is critical for effective self-stretching. Sufficient stabilization of either the proximal or distal attachment of a shortened muscle is necessary but can be difficult to achieve with self-stretching. Every effort should be made to see that restricted structures are stretched specifically and that adjacent structures are not overstretched.
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Application. The guidelines for the intensity, speed, duration, and frequency of stretch that apply to manual stretching are also appropriate for self-stretching procedures. Static stretching for a 30- to 60-second duration per repetition is considered the safest type of stretching for a self-stretching program.
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Self-stretching exercises can be carried out in several ways.
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Using positions for self-ROM exercises described in Chapter 3, a patient can passively move the distal segment of a restricted joint with one or both hands to elongate a shortened muscle while stabilizing the proximal segment (Fig. 4.11 A).
If the distal attachment of a shortened muscle is fixed (stabilized) on a support surface, body weight can be used as the source of the stretch force to elongate the shortened muscle-tendon unit (Fig. 4.11 B).
Neuromuscular inhibition, using PNF stretching techniques, can be integrated into self-stretching procedures to promote relaxation in the muscle that is being elongated.
Low-intensity active stretching (referred to by some as dynamic ROM8), using repeated, short-duration, end-range active muscle contractions of the muscle opposite the shortened muscle is another form of self-stretching exercise.8,161,168
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Mechanical Stretching
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Characteristics. Mechanical stretching devices apply a very low-intensity stretch force (low-load) over a prolonged period of time to create relatively permanent lengthening of soft tissues, presumably due to plastic deformation.
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There are many ways to use equipment to stretch shortened tissues and increase ROM. The equipment can be as simple as a cuff weight or weight-pulley system or as sophisticated as some adjustable orthotic devices or automated stretching machines.11,17,80,95,99,103,110,143 These mechanical stretching devices provide either a constant load with variable displacement or constant displacement with variable loads.
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Effectiveness. Studies17,80 about the efficacy of the two categories of mechanical loading devices base their effectiveness on the soft tissue properties of either creep or stress-relaxation, which occur within a short period of time, as well as plastic deformation, which occurs over an extended period of time.
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Be cautious of studies or product information that report "permanent" lengthening as the result of use of mechanical stretching devices. The term, "permanent," may mean that length increases were maintained for as little as a few days or a week after use of a stretching device has been discontinued. Long-term follow-up may indicate that tissues have returned to their shortened state if the newly gained motion has not been used regularly in daily activities.
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Application. It is often the responsibility of a therapist to recommend the type of stretching device that is most suitable and teach a patient how to safely use the equipment and monitor its use in the home setting. A therapist may also be involved in the fabrication of serial casts or splints.
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Each of the following forms of mechanical stretching has been shown to be effective, particularly in reducing longstanding contractures.
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An effective stretch load applied with a cuff weight (Fig. 4.12) can be as low as a few pounds.99
Some devices, such as the Joint Active Systems" adjustable orthosis (Fig. 4.13), allow a patient to control and adjust the load (stretch force) during a stretching session.17,80
With other devices, the load is preset prior to the application of the splint, and the load remains constant while the splint is in place.
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Duration of Mechanical Stretch
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Mechanical stretching involves a substantially longer overall duration of stretch than is practical with manual stretching or self-stretching exercises. The duration of mechanical stretch reported in the literature ranges from 15 to 30 minutes to as long as 8 to 10 hours at a time17,57,80 or continuous throughout the day except for time out of the device for hygiene and exercise.11 Serial casts are worn for days or weeks at a time before being removed and then reapplied.77 The time frame is dependent on the type of device employed, the cause, severity, and chronicity of impairment, and patient tolerance. The longer durations of stretch are required for patients with chronic contractures as the result of neurological or musculoskeletal disorders rather than healthy subjects with only mild hypomobility.17,77,80,99,103,111,116
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FOCUS ON EVIDENCE
Light and colleagues99 studied nonambulatory, elderly nursing home residents with long-standing bilateral knee flexion contractures and compared the effects of mechanical and manual stretching. Over a 4-week period, twice-daily stretching sessions occurred 5 days per week. Low-intensity, prolonged mechanical stretching (a 5- to 12-lb stretch force applied by a weight-pulley system for 1 hour each session) was applied to one knee, and manual passive stretching was applied to the other knee by a therapist (three repetitions of 1-minute static stretches per stretching session). At the conclusion of the study, the mechanical stretching procedure was found to be considerably more effective than the manual stretching procedure for increasing knee extension. The patients also reported that the prolonged mechanical stretch was more comfortable than the manual stretching procedure, which tended to be applied at a higher intensity. The investigators recognized that the total duration of mechanical stretch (40 hours) was substantially longer over the course of the study than the total duration of manual stretch (2 hours) but believed that the manual stretching sessions were typical and practical in the clinical setting.
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Proprioceptive Neuromuscular Facilitation Stretching Techniques
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PNF stretching techniques,24,74,108,123,138 sometimes referred to as active stretching168 or facilitative stretching,125 integrate active muscle contractions into stretching maneuvers purportedly to inhibit or facilitate muscle activation and to increase the likelihood that the muscle to be lengthened remains as relaxed as possible as it is stretched.
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The traditional explanation of the underlying mechanisms of PNF stretching is that reflexive relaxation occurrs during the stretching maneuvers, as the result of autogenic or reciprocal inhibition. In turn, inhibition leads to decreased tension in muscle fibers and, therefore, decreased resistance to elongation by the contractile elements of the muscle when stretched. However, this explanation has come into question in recent years.
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Current thinking suggests that gains in ROM during or following PNF stretching techniques cannot be attributed solely to autogenic or reciprocal inhibition, which involves the spinal processing of proprioceptive information. Rather, increased ROM is the result of more complex mechanisms of sensorimotor processing, most likely combined with viscoelastic adaptation of the muscle-tendon unit and changes in a patient's tolerance to the stretching maneuver.24,108,138
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Regardless of the ongoing controversy about why PNF stretching techniques are effective, the results of numerous studies have demonstrated that the various PNF stretching techniques increase flexibility and ROM.8,38,52,123,135,168,170 However, the degree of neuromuscular relaxation associated with the PNF stretching maneuvers investigated was not determined in these studies. There is also evidence from some studies108,135 that PNF stretching yields greater gains in ROM than static stretching, but there is no consensus on whether one PNF technique is significantly superior to another.
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Types of PNF Stretching
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There are several types of PNF stretching procedures, all of which have been shown to improve ROM VIDEO 4.1
. They include:
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With classic PNF, these techniques are performed with combined muscle groups acting in diagonal patterns125,126,158 but have been modified in the clinical setting and in a number of studies and resources8,29,68,76,108,123,168 by stretching in a single plane or opposite the line of pull of a specific muscle group. (For a description of the PNF diagonal patterns, refer to Chapter 6.)
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CLINICAL TIP
PNF stretching techniques require that a patient has normal innervation and voluntary control of either the shortened muscle (the range-limiting target muscle) or the muscle on the opposite side of the joint. As such, these techniques cannot be used effectively for patients with paralysis or spasticity resulting from neuromuscular diseases or injury. Furthermore, because PNF stretching procedures are designed to affect the contractile elements of muscle, not the noncontractile connective tissues, they are more appropriate when muscle spasm limits motion and less appropriate for stretching longstanding, fibrotic contractures.
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Hold-Relax and Contract-Relax
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With the HR and CR procedures,29,76,108,123,125,126 the range-limiting target muscle is first lengthened to the point of tissue resistance or to the extent that is comfortable for the patient. The patient then performs a prestretch, end-range, isometric contraction (for about 5 seconds) followed by voluntary relaxation of the range-limiting target muscle. The limb is then passively moved into the new range as the range-limiting muscle is elongated. A sequence for using the HR and CR technique to stretch shortened pectoralis major muscles bilaterally and increase horizontal abduction of the shoulders is illustrated in Figure 4.14.
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NOTE: Although the terms CR and HR often are used interchangeably, in classic PNF, the descriptions of the techniques are not identical. Both techniques are performed in diagonal patterns, but in the CR technique, the rotators of the limb are allowed to contract concentrically while all other muscle groups of the diagonal pattern contract isometrically during the prestretch phase of the procedure. In contrast, in the HR technique, the prestretch isometric contraction occurs in all muscles of the diagonal pattern.126,158
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Practitioners in the clinical and athletic training settings have reported that the HR and CR techniques appear to make passive elongation of muscles more comfortable for a patient than manual passive stretching.76 A commonly held assumption is that neuromuscular relaxation, reflected by a decrease in EMG activity, possibly as the result of autogenic inhibition, occurs following the sustained, prestretch, isometric contraction of the muscle to be lengthened.102,125,126 Some investigators49,108 have challenged this assumption, attributing the gains in flexibility to the viscoelastic properties of the muscle-tendon unit. Their studies revealed evidence of a postcontraction sensory discharge (increased EMG activity) in the range-limiting muscle, suggesting that there was lingering tension in the muscle after the prestretch isometric contraction and that the range-limiting muscle was not reflexively relaxed prior to stretch. However the results of another study30 indicated no evidence of a postcontraction elevation in EMG activity with the HR or CR techniques.
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In light of the mixed evidence about the degree of neuro-muscular relaxation occurring, practitioners must determine the effectiveness of the HR or CR techniques based on the responses of their patients.
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PRECAUTION: It is not necessary for the patient to perform a maximal isometric contraction of the range-limiting target muscle prior to stretch. Multiple repetitions of maximal prestretch isometric contractions have been shown to result in an acute increase in arterial blood pressure, most notably after the third repetition.31 To minimize the adverse effects of the Valsalva maneuver (elevation in blood pressure associated with a high-intensity effort), have the patient breathe regularly while performing submaximal (low-intensity) isometric contractions held for about 5 seconds with each repetition of the HR or CR procedure. From a practical perspective, a submaximal contraction is also easier for the therapist to control if the patient is strong.
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Another PNF stretching technique is the agonist contraction (AC) procedure. This term has been used by several authors30,76,123 but can be misunderstood. The "agonist" refers to the muscle opposite the range-limiting target muscle. "Antagonist," therefore, refers to the range-limiting muscle. Think of it as the short muscle (the antagonist) preventing the full movement of the prime mover (the agonist). Dynamic range of motion (DROM)8 and active stretching168 are other terms that have been used to describe the AC procedure.
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To perform the AC procedure, the patient concentrically contracts (shortens) the muscle opposite the range-limiting muscle and then holds the end-range position for at least several seconds.24,30,76,123 The movement of the limb is controlled independently by the patient and is deliberate and slow, not ballistic. In most instances, the shortening contraction is performed without the addition of resistance. For example, if the hip flexors are the range-limiting target muscle group, the patient performs end-range, prone leg lifts by contracting the hip extensors concentrically; the end-range contraction of the hip extensors is held for several seconds. After a brief rest period, the patient repeats the procedure.
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Increased muscle length and joint ROM using the AC procedure have been reported. However, when the effectiveness of the AC technique has been compared to static stretching, the evidence is mixed.
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FOCUS ON EVIDENCE
Several studies have evaluated the effectiveness of the AC procedure for improving flexibility and ROM. Two studies compared the effect of the AC procedure, referred to as DROM, to static stretching of the hamstrings of healthy subjects who participated in 6-week stretching programs. In one study,161 DROM was found to be as effective as static stretching, but in the other study,8 one daily repetition of a 30-second static stretch was almost three times as effective in increasing hamstring flexibility as six repetitions daily of DROM with a 5-second, end-range hold.
In a study of young adults with hypomobile hip flexors and periodic lumbar or lower-quarter pain, investigators compared "active stretching" using the AC procedure to static passive stretching.168 Both techniques resulted in increased hip extension with no significant difference between the active and passive stretching groups.
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In addition to the results of studies on the AC stretching procedure, clinicians have observed the following.
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The AC technique seems to be especially effective when significant muscle guarding restricts muscle lengthening and joint movement and is less effective in reducing chronic contractures.
This technique is also useful when a patient cannot generate a strong, pain-free contraction of the range-limiting muscle, which must be done during the HR and CR procedures.
This technique is also useful for initiating neuromuscular control in the newly gained range to re-establish dynamic flexibility.
The AC technique is least effective if a patient has close to normal flexibility.
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PRECAUTIONS: Avoid full-range, ballistic movements when performing concentric contractions of the agonist muscle group. Rest after each repetition to avoid muscle cramping when the agonist is contracting in a very shortened portion of its range.
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Classic PNF theory suggests that when the agonist (the muscle opposite the range-limiting muscle) is activated and contracts concentrically, the antagonist (the range-limiting muscle) is reciprocally inhibited, allowing it to relax and lengthen more readily.125,130 However, the theoretical mechanism of reciprocal inhibition has been substantiated only in animal studies.127 Evidence of reciprocal inhibition during the AC procedure has not been demonstrated in human subjects24,127,138 In fact, an increase of EMG activity, not reciprocal inhibition, has been identified in the range-limiting muscle during application of the AC stretching procedure.30,123
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Hold-Relax with Agonist Contraction
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The HR-AC stretching technique combines the HR and AC procedures. The HR-AC technique is also referred to as the CR-AC procedure24 or slow reversal hold-relax technique.158 To perform the HR-AC procedure, move the limb to the point that tissue resistance is felt in the range-limiting target muscle; then have the patient perform a resisted, prestretch isometric contraction of the range-limiting muscle followed by voluntary relaxation of that muscle and an immediate concentric contraction of the muscle opposite the range-limiting muscle.30,125,158
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For example, to stretch knee flexors, extend the patient's knee to a comfortable, end-range position and then have the patient perform an isometric contraction of the knee flexors against resistance for about 5 seconds. Tell the patient to voluntarily relax and then actively extend the knee as far as possible, holding the newly gained range for several seconds.
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FOCUS ON EVIDENCE
Studies comparing two PNF stretching procedures produced differing results. In one study,52 the HR-AC technique produced a greater increase in ankle dorsiflexion range than did the HR technique. Both PNF techniques produced a greater increase in range of ankle dorsiflexion than did manual passive stretching. However, in another study,76 there was no significant difference between the use of the HR and HR-AC techniques.
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PRECAUTIONS: Follow the same precautions as described for both the HR and AC procedures.
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Integration of Function into Stretching
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Importance of Strength and Muscle Endurance
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As previously discussed, the strength of soft tissue is altered when it is immoblized for a period of time.25,115 The magnitude of peak tension produced by muscle decreases, and the tensile strength of noncontractile tissues decreases. A muscle group that has been overstretched because its opposing muscle group has been in a shortened state for an extended period of time also becomes weak.87,96,97 Therefore, it is critical to begin low-load resistance exercises to improve muscle performance (strength and endurance) as early as possible in a stretching program.
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Initially, it is important to place emphasis on developing neuromuscular control and strength of the agonist, the muscle group opposite the muscle that is being stretched. For example, if the elbow flexors are the range-limiting muscle group, emphasize contraction of the elbow extensors in the gained range. Complement stretching the hamstrings to reduce a knee flexion contracture by using the quadriceps in the new range. Early use of the agonist enables the patient to elongate the hypomobile structures actively and use the recently gained ROM.
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As ROM approaches a "normal" or functional level, the muscles that were shortened and then stretched must also be strengthened to maintain an appropriate balance of strength between agonists and antagonists throughout the ROM. Manual and mechanical resistance exercises are effective ways to load and strengthen muscles, but functional weight-bearing activities, such as those mentioned below also strengthen antigravity muscle groups.
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Use of Increased Mobility for Functional Activities
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As mentioned previously, gains in flexibility and ROM achieved as the result of a stretching program are transient, lasting only about 4 weeks after cessation of stretching.166 The most effective means of achieving permanent increases in ROM and reducing functional limitations is to integrate functional activities into a stretching program to use the gained range on a regular basis. Use of functional activities to maintain mobility lends diversity and interest to a stretching program.
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Active movements should be within the pain-free ROM. Examples of movements of the upper or lower extremities or spine that are components of daily activities include reaching, grasping, turning, twisting, bending, pushing, pulling, and squatting to name just a few. As soon as even small increases in tissue extensibility and ROM have been achieved, have the patient use the gained range by performing motions that simulate functional activities. Later, have the patient use all of the available ROM while actually doing specific functional tasks.
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Functional movements that are practiced should complement the stretching program. For example, if a patient has been performing stretching exercises to increase shoulder mobility, have the patient fully use the available ROM by reaching as far as possible behind the back and overhead when grooming or dressing or by reaching for or placing objects on a high shelf (Fig. 4.15). Gradually increase the weight of objects placed on or removed from a shelf to strengthen shoulder musculature simultaneously.
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If the focus of a stretching program has been to increase knee flexion after removal of a long-leg cast, emphasize flexing both knees before standing up from a chair or when stooping to pick up an object from the floor. These weight-bearing activities also strengthen the quadriceps that became weak while the leg was immobilized and the quadriceps were held in a shortened position.
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