Acute stretching

[tim290280]

Thought this was extremely relevant after the poll in the training forum.

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.

 

[tim290280]

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.

 

[tim290280]

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[tim290280]

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[philosopher]

Great read tim
So the fact remain, you need as much flexibility as your given daily activity/sport requires plus a little bit more as a safety allowance. More isn't better and could be worse

 

[CJU]

that cleared some stuff up for me. obviously stretching can increase performance, but what about look? can stretching induce or help induce hypertrophy?

 

[tim290280]

^^ I don't really see a huge difference between performance and appearance. Generally you will look better when you are able to train better.

Directly though, stretching will not, to my knowledge, induce hypertrophy. But it does aid in improving your muscle condition, length, and joint mobility that will aid in your hypertrophy training. So in a holistic sense it does.

 

[Méthode naturelle]

Great read tim
So the fact remain, you need as much flexibility as your given daily activity/sport requires plus a little bit more as a safety allowance. More isn't better and could be worse

Depends what you want out of life

Flexibility can certainly be advantageous in life. I see a lot of people in the gym who neglect certain types of conditioning in the gym.

Like the man who is frightened to get on the tredmill because he thinks he will lose muscle

 

[Hypocrisy86]

Stretching after a workout is helpful yes?

 

[Tonyk212000]

Hypocrisy i think so. Im a big fan of dc training and love doing the stretches after excercise. Your muscle has a fascia sheet over it. This sheet is wrapped tightly around your muscle and at times can prevent it from growing. Once your done working out your muscle start recovering and regrowing. So the best thing to do is stretch the fascia out and provide for the room to grow. Yes your muscles can grow without stretching it but it can at a slightly faster rate if you streth the fascia.

 

[Hypocrisy86]

Thanks, man!

 

[bambam55]

I stretch a lot after lifting especially in the legs. Its important for me to maintain flexibility in the hips and legs with football, but most of all I just feel better after stretching. I feel that I recover faster and it works the kinks out of the muscles.

 

[Hypocrisy86]

^ yea it does help. even heavy leg presses don't deter my ability to stand and kick my right leg above my waist.

 

[tim290280]

Hypocrisy i think so. Im a big fan of dc training and love doing the stretches after excercise. Your muscle has a fascia sheet over it. This sheet is wrapped tightly around your muscle and at times can prevent it from growing. Once your done working out your muscle start recovering and regrowing. So the best thing to do is stretch the fascia out and provide for the room to grow. Yes your muscles can grow without stretching it but it can at a slightly faster rate if you streth the fascia.

Did you even read the article? :angrydude: I originally posted this because people were blindly talking up "extreme" DC style stretching, which is bad for your joints.

 

[Achilles]

Havent noticed this article before. Its a great read Tim. Stretching is a very interesting subject imo.

 

[Big_Guns_Lance]

Great read there Tim

 

[TJ]

I didn't read the whole article, just the absract, but static stretches are best performed at night after a warm shower. I do agree with Tim that DC stretches just push the limit too much. You shouldn't put yourself in pain when doing stretches.

 

[Tonyk212000]

You shouldn't put yourself in pain when doing stretches.

Personally Im going to have to disagree with all of you on the pain factor. You can bring all the scientific information you want but if you stretch and you dont feel the stretch which in my opinion has some pain to it you are never going to advance. As of right now I can do the splits and have been able to do them for about 4 years now. The only way I was able to achieve this was to do the movement of the splits and push down to try and advance. This required some pain to push down a few more inches to try and do the splits. Whenever you stretch something you are going to feel pain and that pain is the muscle stretching. The only way you will be able to go from touching your ankles to touching the ground when stretching your hams is to push yourself throught the pain and reach farther. If you stay stretching at the ankles and never feel it you will never be able to stretch farther. I guarentee gymnasts felt pain when stretching to achieve there flexibility they have now.

 

[tim290280]

^^ You are talking about feeling a stretch not the onset of pain that Wolf is talking about. Joint integrity and ligament and tendon start to be compromised when you push a pain barrier. Most gymnasts have all sorts of joint issues and hypermobility. The ones that don't achieved their flexibility through less agressive stretching.

 

[Tonyk212000]

^^ You are talking about feeling a stretch not the onset of pain that Wolf is talking about. Joint integrity and ligament and tendon start to be compromised when you push a pain barrier. Most gymnasts have all sorts of joint issues and hypermobility. The ones that don't achieved their flexibility through less agressive stretching.

My bad I didnt no he was talking about joint pain , I was thinking actually pain in the muscle. Oopsy