No Difference in Pre- and Postexercise Stretching on Flexibility

[3XL]

The Journal of Strength and Conditioning Research: Vol. 21, No. 3, pp. 780–783.

No Difference in Pre- and Postexercise Stretching on Flexibility
Barry B. Beedle, Summer N. Leydig, and Jennifer M. Carnucci


Department of Health and Human Performance, Elon University, Elon, North Carolina 27244

ABSTRACT

Beedle, B.B., S.N. Leydig, and J.M. Carnucci. No difference in pre- and postexercise stretching on flexibility. J. Strength Cond. Exerc. 21(3):780–783. 2007.—

According to the American College of Sports Medicine (1), there is limited information about when to stretch during an exercise session. The purpose of this study was to determine if the placement of static stretching, either before or after a workout, would affect flexibility in the hip, knee, and ankle.

Thirty college-age men (n = 12) and women (n = 18) volunteered to participate. Nine were highly trained, 13 were moderately trained, and 8 were sedentary.

Subjects participated in both treatments, which were randomly assigned and were 48–72 hours apart.

In one treatment, subjects warmed-up first by walking on a treadmill for 5 minutes at approximately 50% of their age-predicted maximum heart rate, and then performed 3 static stretches: quadriceps, hamstrings, and calf muscles. Each stretch was held 3 times, 15 seconds each. Next, flexibility measurements were determined for the hip, hamstrings, and ankle using a goniometer.

The other treatment consisted of performing 20 minutes of walking or jogging at a moderate intensity, then the same stretching exercises were performed and the same flexibility measurements were taken.

Reliability coefficients ranged from 0.90–0.96.

There were no significant differences in any of the flexibility measurements except for hip flexibility, which approached significance (p = 0.06) and therefore favored stretching after the workout.

The placement of stretching, before or after a workout, does not make a difference in its effect on flexibility.
No Difference in Pre- and Postexercise Stretching on Flexibility

[LangeMan]

Ik lees dat het 20 minuten joggen betreft en dat het daarop niet veel uitmaakt behalve bij de heup, misschien is het bij krachtraining weer heel anders.

[philosopher]

Nog een leuke

Cochrane Database Syst Rev. 2007 Oct 17;(4):CD004577. Links
Stretching to prevent or reduce muscle soreness after exercise.
Herbert R, de Noronha M.

BACKGROUND: Many people stretch before or after (or both) engaging in athletic activity. Usually the purpose is to reduce risk of injury, reduce soreness after exercise, or enhance athletic performance. OBJECTIVES: The aim of this review was to determine effects of stretching before or after exercise on the development of post-exercise muscle soreness. SEARCH STRATEGY: We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (to April 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2006, Issue 2), MEDLINE (1966 to May 2006), EMBASE (1988 to May 2006), CINAHL (1982 to May 2006), SPORTDiscus (1949 to May 2006), PEDro (to May 2006) and reference lists of articles. SELECTION CRITERIA: Eligible studies were randomised or quasi-randomised studies of any pre-or post-exercise stretching technique designed to prevent or treat delayed-onset muscle soreness (DOMS), provided the stretching was conducted soon before or soon after exercise. To be eligible studies must have assessed muscle soreness or tenderness. DATA COLLECTION AND ANALYSIS: Methodological quality of the studies was assessed using the Cochrane Bone, Joint and Muscle Trauma Group's methodological quality assessment tool. Estimates of effects of stretching were converted to a common 100-point scale. Outcomes were pooled in a fixed-effect meta-analysis. MAIN RESULTS: Of the 10 included studies, nine were carried out in laboratory settings using standardised exercise protocols and one involved post-exercise stretching in footballers. All participants were young healthy adults. Three studies examined the effects of stretching before exercise and seven studies investigated the effects of stretching after exercise. Two studies, both of stretching after exercise, involved repeated stretching sessions at intervals of greater than two hours. The duration of stretching applied in a single session ranged from 40 to 600 seconds.All studies were small (between 10 and 30 participants received the stretch condition) and of questionable quality.The effects of stretching reported in individual studies were very small and there was a high degree of consistency of results across studies. The pooled estimate showed that pre-exercise stretching reduced soreness one day after exercise by, on average, 0.5 points on a 100-point scale (95% CI -11.3 to 10.3; 3 studies). Post-exercise stretching reduced soreness one day after exercise by, on average, 1.0 points on a 100-point scale (95% CI -6.9 to 4.8; 4 studies). Similar effects were evident between half a day and three days after exercise. AUTHORS' CONCLUSIONS: The evidence derived from mainly laboratory-based studies of stretching indicate that muscle stretching does not reduce delayed-onset muscle soreness in young healthy adults.

[philosopher]

Voor diegene die nog wat meer wil weten:

Strength and Conditioning Journal: Vol. 28, No. 6, pp. 66–74.

Stretching: Acute and Chronic? The Potential Consequences
Mike Stone, PhD, Michael W. Ramsey, PhD, and Ann M. Kinser

ABSTRACT

Stretching is commonly used by many athletes in different sports. Although acute stretching, as part of a warm-up, can enhance range of motion, it may also reduce performance. Acute stretching can reduce peak force, rate of force production, and power output. Chronic stretching may enhance performance, although the mechanism is unclear. Acute stretching has little effect on injury. However,chronic stretching (not part of warm-up) may have some injury reduction potential.

Key Words: acute stretching, chronic stretching, range of motion

Introduction

Stretching can be defined as the actof applying tensile force to lengthen muscle and connective tissue. Often stretching is performed as part of a warm-up prior to physical exertion. Typically, stretching is used to enhance the range of motion (ROM) about a joint (flexibility). The resulting enhancement may be viewed as acute (temporary) or chronic.

There are many different types of stretching that can be performed. A quick look at the internet (under “stretching”) offers a variety of stretching types and methods, including:

Ballistic stretching

Dynamic stretching

Active stretching

Passive (or relaxed) stretching

Static stretching

Isometric stretching

Proprioceptive neuromuscular facilitation stretching


Although in some cases the nature of these methods is essentially the same, it gives the coach/athlete a wide variety of methods from which to choose when acutely or chronically stretching.

Although, the exact timing and degree of stretching varies somewhat from sport to sport, there are basically 2 forms of stretching taking place on a regular basis among athletes: first is acute stretching (as part of a warm-up process), and second is chronic stretching that is often quite extensive and usually occurs after a training session. Athletes and coaches commonly hold 2 beliefs concerning these 2 forms of stretching: (a) acute stretching (part of warm-up) may increase performance and will reduce the injury potential of exercise; (b) chronic stretching will increase performance, reduce aches and pains, and reduce the injury potential of exercise and sports performance.

However, data exist indicating that these beliefs may not be completely true. The purpose of this paper is to answer several basic questions concerning stretching and its relationship to sports performance, with a particular focus on gymnastics.



Will Warm-Up (Acute) Stretching Produce a Better Performance?

Table 1 shows the results of studies dealing with the relationship of various activities and various performance characteristics that would have effects on sport. Although not all studies show a decrease in performance, the large majority do indicate that acute stretching can decrease subsequent performance, particularly for maximum strength– and explosive strength–related movements. So, for a sport such as gymnastics, in which explosive strength is quite important, such a loss of explosive capability may reduce the ability to perform.

The underlying mechanisms that can reduce performance subsequent to acute stretching are not necessarily apparent or easily understood. To begin to understand why acute stretching may reduce performance, a brief discussion of how stretching affects ROM is in order. There are basically 2 mechanistic possibilities that may have an effect individually or in combination: (a) stretching alters ROM by altering the structure and properties of soft tissue (muscle and connective tissue); (b) there is an increase in pain tolerance.

Tissue stiffness is the ability of a tissue to resist change in length and is represented by a change in force per change in length (F/L). A decreased or increased stiffness may alter the stress-strain curve (changes in force when muscle or connective tissue is lengthened or shortened by stretching). Figure 1 (36) shows a passive stress-strain curve in which a tissue is being stretched until failure. Note that to a point, the greater the lengthening of the tissue the greater the force produced. The amount of energy that is absorbed by the tissue before failure is a function of its tensile strength. Therefore, the more energy absorbed, the stronger and the more stretch resistant the tissue. The stiffer the tissue, the more it resists the stretch, and there are 2 possible results: (a) the rate at which force rises is faster; (b) the failure point of the tissue may be reached faster.

Muscle can also be activated to resist a stretching load (e.g., eccentric contractions). Thus, muscle tissue has active stiffness properties. Contraction during stretching can take up the slack in the series elastic elements faster and result in a faster rate of force production and an increased amount of force before failure (36).

A very stiff tissue would require more force to stretch it to a given length. So tissue stiffness could (theoretically) inhibit flexibility. Therefore, an acute exercise reducing tissue stiffness could enhance flexibility. However, in the normal intact human, changes in the length of a muscle (or muscles) also alter the feedback to the nervous system. For example, a less stiff muscle would produce less force at a given length, and the nervous system senses this difference. Thus, alterations in muscle stiffness (active or passive) could change how the nervous system reacts to a given muscle length. Therefore, a change in active or passive muscle stiffness could also effect the stretch reflex characteristics and tissue elastic properties (less energy stored for elastic recoil) such that force transmission is disrupted/muted, decreasing force magnitude, rate of force development, and power output.

Some evidence indicates that an increased ROM as a result of stretching is related to reduced tissue stiffness (20). However, the majority of studies indicate that although tissue viscosity may be altered, muscle stiffness and elasticity are largely unaffected by acute stretching as part of a warm-up (11) or chronic stretching over a 3- to 4-week period (21, 34, 37) and that alterations in ROM after stretching are more related to increased pain tolerance (21, 37). On the other hand, repeated and prolonged stretching for 1 hour (7) adversely affected active and passive muscle stiffness, and 30 sessions of static stretching produced a decrease in passive muscle stiffness (20). The decrease in active tissue stiffness as a result of prolonged stretching could be a fatigue-induced phenomenon rather than simply a stretch result (5, 24). Thus, increased ROMs as a result of stretching may result from decreased muscle stiffness but this appears to be more likely caused by altered tissue viscosity and pain tolerance.

Interestingly, maximum strength and strength training effects appear to be associated with increased active and passive muscle stiffness that is independent of ROM alterations (17,34,37,55). An increase in muscle stiffness appears to be associated with enhanced strength (66) and various types of performances, including the vertical jump and improved running (i.e., enhance running economy; Figure 2 ). Thus, a loss of performance associated with acute stretching could be associated with a decrease in muscle stiffness.

Stretching has also been associated with muscle damage. In mice, Black and Stevens (9) found that acutely stretching muscle fibers 5 % beyond resting resulted in a 5% loss of isometric force production. Strains (stretching), as low as 20% beyond resting length, have been related to muscle damage and decreased force in humans (38). So vigorous stretching could induce enough muscle damage to reduce maximum strength and explosive strength. However, in the authors' opinion, it is unlikely that chronic stretching in well-trained athletes would continue to induce tissue damage. Otherwise, one would expect chronic muscle soreness among advanced and elite athletes, and this clearly is not the case.

A finding noted in most of the performance studies indicates that acute stretching as a part of warm-up reduces maximum strength (force magnitude) and several associated variables, such as rate of force development and power output (8, 46, 53). Additionally, a decreased H-reflex has been noted (6, 7, 20). The H-reflex is a monosynaptic reflex elicited by stimulating a nerve, particularly the tibial nerve, with an electric shock. Thus, it appears that stretching acutely as part of a warm-up can negatively alter force production, power output, and stretch-shortening cycle characteristics such that strength and performance, including such explosive performances as gymnastics, can be compromised. This compromise may be associated with alterations in muscle stiffness (Figure 2) .



Will Chronic Stretching (Non–Warm-Up) Improve Performance?

Many athletes stretch after a training session. The belief is that over the long term, this practice may reduce injury and perhaps enhance performance. Table 2 shows studies that have investigated long-term stretching and performance. These studies generally show that performance, particularly maximum strength and explosive strength performances, were enhanced. When the studies are taken as a whole, the degree of enhancement appears to be small, perhaps 3 to 4 %. However, it should be remembered that in high-level sports, a small percentage of improvement can actually be a lot. For example, in the last 2 Olympics, the difference between first and fourth place (for most sports) was less than 1.5 %. The mechanisms underlying enhanced performance, as a result of chronic stretching, are unclear at best.

[philosopher]

Due to position requirements for some sports, such as weightlifting, diving, and particularly gymnastics, it becomes obvious that an increased ROM would be advantageous. If tissue stiffness could be reduced, one might argue that movement economy would be enhanced. In this context, Godges et al. (19) noted that among very inflexible patients, stretching could produce performance (gait) enhancements. However, the primary alteration (3- to 4-week studies) appears to be stretch-pain-tolerance and not change in visco-elasticity (21, 37). Thus, it is doubtful that muscle stiffness and movement economy would be substantially altered as a result of stretching.

Another possibility is that stretching induces additional hypertrophy. Chronic stretch (24 h/d) causes some muscle damage and chronic reflexive activity and results in muscle hypertrophy in animals. Acute stretching (5% of initial length) can cause some muscle damage (at least in untrained animals) and result in a force deficit (9). However, it is doubtful that the stretching used in training athletes would be enough to cause sufficient damage to tissue to increase hypertrophy and force-producing capability, especially in well-trained strength/power athletes. Therefore, the exact mechanisms that underlie the small but positive performance improvements that often accompany increased flexibility remain elusive. Perhaps the underlying mechanism explaining increased performance is simply a greater ROM resulting from greater pain tolerance.

Will Stretching (Acute or Chronic) Affect Injury Rates?

Although flexibility is often believed to be related to injury, particularly muscular injury, it is not clear as to how it is related (57). The mechanism that is usually associated with the role of flexibility in musculo-tendinous injury deals with stretching the tissue beyond its normal active limits. For example, in sports movements in which the tissue does not have enough elasticity to compensate for additional stretch, the tissue will tear. If the average person jumped into a fore-aft split, typical of gymnastics, most often there would be considerable injury to the musculo-tendinous tissues (not to mention a few other items). If high levels of flexibility are gained through stretching, such as takes place among gymnasts, this position can typically be achieved without problems. Although this example is likely related to flexibility and is a good reason to enhance flexibility, not all injuries can be attributed to ROM characteristics. For example, the majority of pulled (torn) muscles, such as those affected when a sprinter pulls a hamstring, do not appear to occur as a result of overextension of the tissues. Many of these non–limit-stretching injuries appear to occur during eccentric loading but within normal ROMs (58, 62). Furthermore, the injury potential appears to rise as the eccentric loading produces faster strain rates (61). Thus, some other mechanism must be responsible for the non–limit-stretch–induced injuries.

One mechanistic possibility responsible for non–limit-stretch injuries is increased muscle stiffness, particularly when the muscle is active, such as during eccentric loading (54, 58). It is possible that as external eccentric forces are imposed upon stiff musculo-tendinous units that are less compliant, less force can be absorbed before injury occurs. So a more compliant tissue system has a cushioning effect, reducing the trauma on the muscle fibers and resulting in less damage (65). Some evidence indicates that greater passive muscle stiffness, as measured by flexibility, is associated with more muscle damage and subsequent loss of strength and degree of delayed soreness as a result of eccentric contractions (41). Thus, a stiffer tissue may increase the potential for injury. Because strength training can increase muscle stiffness, it is possible that the stronger muscle is now more susceptible to injury. However, the available data do not completely support this idea; although strength training increases muscle stiffness, it can also reduce injury potential. As tissue is stretched it absorbs energy, and active muscles are capable of absorbing more energy than passive muscles (36). A stronger muscle would have a greater energy absorbance reserve before tearing during eccentric actions (35). Thus, strength training, particularly eccentric training, may actually reduce rather than increase injury to the musculo-tendinous unit.

Table 3 shows studies that deal with factors related to injury and injury reduction during physical activity. Several factors appear to predispose one to increased injury, such as previous injury. Interestingly, with the exception of joints showing extreme ROMs, most studies indicate that reduced flexibility shows little relationship to typical sports injuries. Neither acute (50) nor chronic (23) stretching appears to effect a significant reduction in physical activity–related injuries. Indeed, Thacker et al. (62), in an extensive review of the flexibility literature that included 361 articles dating back into the 1950s, concluded that there is little relationship between stretching (e.g., increased ROM) and injury. Thus, there is little evidence that stretching and improved ROM effects a lower injury rate.

This discussion brings up an interesting dilemma: if acute (as part of a warm-up) stretching reduces performance and good flexibility is a necessity in performance, as in gymnastics, then:


A.How long do you have to wait before the effect (reduce performance) wears off? Unfortunately, this problem has not been well studied. Obviously, the effect of reduced explosiveness does wear off, but exactly how long it takes is unknown. The authors' observations suggest that the wear-off time may last as long as 1 to 2 hours and that differences in wear-off time may be individual characteristics. Part of the reason for differences in the wear-off time likely involves determining what type of stretching was used the degree of inhibition and the presence or absence of fatigue, as well as individual differences.



B.What if there is an intervention between the acute flexibility exercise and the subsequent performance? This question deals with this idea: flexibility can be acutely enhanced by stretching as part of a warm-up; however, this reduces explosiveness during performance. What happens if some explosive movement takes place between the stretching and the subsequent performance? Some data indicate that in fact the intervening exercise can reduce the negative effect of stretching on explosiveness, at least to an extent (69). However, it is not known to what extent the alterations in flexibility can be retained.



C.Is there a warm-up method in which flexibility is gained but performance is either not adversely affected or enhanced? Vibration has been shown to acutely (and chronically) enhance explosive performance (28, 51, 52). Vibration has also been shown to acutely (and chronically) enhance flexibility resulting from stretching (3, 27, 56). When the 2 are combined, it may be possible to enhance flexibility without altering explosiveness. Cochrane and Stannard (10) found that women field hockey players using a vibration platform while in a stretched position for 5 minutes before exercise can increase both flexibility and explosiveness as measured by jumping.

Conclusion

Stretching can alter the ROM about a joint and improve flexibility. However, stretching as part of a warm-up may reduce performance. It is unclear whether or not acute stretching reduces muscle stiffness or increases pain tolerance (or both). Indeed, most available data indicates acute performance reduction can occur and that it may be related to decreased tissue stiffness or alterations in nervous system components of the stretch-shortening cycle, such as the myototic reflex. These alterations in turn can result in a decreased maximum strength and explosiveness and inferior performances. Chronic stretching may enhance performance, although the mechanism is unclear. In such sports as gymnastics, in which great ranges of motion are clearly necessary for performance, it becomes obvious that flexibility is a primary ingredient. Acute stretching seems to have little effect on injury. However, chronic stretching (not part of a warm-up) may have some injury reduction potential.

Several questions concerning stretching remain to be answered. For example, how long do the negative effects of acute stretching on explosiveness last? Cooperative efforts between USOC Sports Science, East Tennessee State University, and Appalachian State University are currently under way to begin answering these questions.

[philosopher]

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