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A quick internet search on stretching reveals that, if physiologists were a bit more belligerent, the question of whether or not to stretch after exercise is something actual wars could be fought over.

As I am not trained in this field, I have come across explanations for both extremes (stretching is vastly important vs. stretching is actually harmful) that both seemed "reasonable" to me.

It would be great if a skeptic with a good understanding in physiology could point me to those studies that give a good answer, together with an understandable explanation that is accepted by the scientific community?

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This topic has been covered over at fitness fitness.stackexchange.com/questions/455/… (One of the best answers on any SE site btw) –  Doug T. Apr 11 '11 at 1:09
    
Ah. I didn't check whether there was such a SE site :) Thank you. –  Lagerbaer Apr 11 '11 at 2:49
    
I cannot seem to vote to close for duplicates found on other SE sites, though. Maybe an admin can do this? –  Lagerbaer Apr 11 '11 at 3:26
    
There is no concept of closing as a duplicate on another site. Each site is autonomous. This is a rare case of where the question might actually be appropriate on BOTH sites-- one set of answer from the point of view of an expert on the subject, the other from a skeptic challenging the science. –  Robert Cartaino Apr 14 '11 at 22:20
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Well, the answer at fitness-SE is quite thoroughly researched. I could reference it and answer my own question, though. –  Lagerbaer Apr 14 '11 at 22:34

3 Answers 3

up vote 18 down vote accepted
+50

As you mentioned stretching is clearly a very controversial subject

Instead, use of stretching as a prevention tool against sports injury has been based on intuition and unsystematic observation rather than scientific evidence. (Source)

A second major reason that many coaches and athletes still view static stretching as an important preactivity ritual is the belief that it reduces the likelihood of subsequent injury. This belief is based on the idea that a "tight" muscle-tendon unit is less extensible without stretching, which means that its tolerance for elongation is lower, This intuitive concept has resulted in a widespread belief that stretching will prevent muscle and tendon strain (Source)

Like many sports physicians, Dr. Bartoli tells her patients that rather than stretching before physical activity, they should do the sporting activity at 50 percent of the target intensity. (Source)

Before I continue I should note that I have found no study that focused on stretching after working out. But based on the results from other literature reviews, I don't think the effect after a workout is much different. Also the lack of scientific interest in the topic should make one highly skeptical as well.

Shrier points out several important points to consider:

  • Both the muscle-tendon unit and the joint capsule may limit ROM [range of motion]. Flexibility is usually considered the ROM limited by muscle-tendon, and mobility is usually considered the ROM limited by capsule/ligament.
  • Stretching must be differentiated from ROM. There are many individuals who have excellent ROM but never stretch, and many individuals who stretch but continue to have limited ROM. Therefore, different injury rates in people with different ROMs may not be related to the effect of stretching, but rather to the underlying interindividual variation in tissue properties, anatomy, etc.
  • Stretching immediately before exercise may have different effects than stretching at other times and should be considered as a separate intervention. Whereas there is considerable amount of clinical data on stretching immediately before exercise, there is much less data on stretching at other times.
  • Some people claim that negative results in some studies are due to improper stretching technique. Because the effect of stretching are believed to occur through changes in stiffness and ROM, an "improper" technique implies that the ROM is not increased. If ROM is increased without causing an immediate injury, then by definition the stretches were done properly.
  • Warm-up is not synonymous with stretching. In the colloquial sense, warm-up means any activity performed before participating in sport. Used in this sense, stretching is only one component of warm-up, and if stretching is included in the pre-exercise activity, I explicitily state that stretching was used. The other component of warm-up is participating in an activity that requires active muscle contractions. This type of warm-up can be divided into general or sport-specific warm-up. In a general warm-up, the objective is to increase body temperature. ... In sport-specific warmp-up, the acitvity is the same but performed at a lower intensity. Be aware that the mechanism of action will dictacte whether one type of warm-up is superior to another.
  • The term "dynamic stretching" is currently used differently by different people, but in essense it refers to stretching of a muscle by contracting and relaxing the antagonist muscle. One should note that dynamic stretching includes both classical stretching and warm-up at the same time. Because dynamic stretching includes both classical stretching and warm-up at the same time. Because dynamic stretching requires the muscles to contract, other possible mechansms include central programming of muscle contraction/coordiantion and decreased fatigue through increased warm-up activity. Those who promote dynamic stretching as a method to prevent injury should provide some evidence that supports their claim.

After discussing many articles he concludes:

A review of the clinical evidence strongly suggests that pre-exercise stretching does not prevent injury, and that the evidence on stretching at other times suggests that it may be beneficial but is too limited to make definitive recommendations at this time. Considering that these results are contrary to many people’s beliefs, it seems prudent to review why some people ever believed stretching before exercise was so beneficial. There appear to be six general arguments that have been proposed in the past.

  • First, paraphrasing an old Chinese saying, “that which does not bend, breaks.” However, when a tree bends, the force (i.e., the wind) changes from a perpendicular force to a longitudinal force; it is much easier to break a stick by applying a perpendicular force to the middle in comparison with longitudinal forces at the end. In stretching a muscle prior to activity, we do not alter the direction of force at the time of injury, and the analogy is inappropriate.
  • Second, compliance refers to the length change that occurs when a force is applied, but is not necessarily related to a tissue’s resistance to injury. For example, even though a balloon will stretch before it bursts (high compliance), a sphere made of metal with the same thickness as the balloon might never stretch (low compliance) and still withstand extremely high pressures.
  • Third, if muscle compliance is increased with warming from 25 °C to 40 °C, the muscle ruptures at a longer length but absorbs less energy. Which is more important, length or energy absorbed? Although muscles are sometimes injured when stretched beyond their normal length of motion, most authors believe that the majority of injuries occur within the normal ROM during eccentric activity, and that the most important variable with respect to muscle injury is the energy absorbed by the muscle Finally, the reader must remember that the damage occurs at the level of the sarcomere and not the whole muscle. Therefore, if there is excessive sarcomere lengthening so that the actin and myosin filaments no longer overlap, the force is transmitted to the cytoskeleton of the muscle fiber, and damage occurs. This occurs within the normal ROM, because sarcomere length within the muscle is heterogeneous; some sarcomeres lengthen during a contraction at the same time as others are shortening. Therefore, it appears that it is the sarcomere length that is related to most exercise-related muscle strains, rather than the total muscle length. Under this hypothesis, an increase in total muscle compliance is irrelevant.
  • Fourth, overstretching a muscle can certainly produce damage. However, even strains as little as 20% beyond resting fiber length, as one would expect with “correct” stretching techniques, can produce damage in isolated muscle preparations. Therefore, the basic science evidence suggests that “correct” stretching techniques may be more difficult to define than previously thought.
  • Fifth, we have seen that the increased ROM with stretching is partly due to an analgesic effect. This may explain some preliminary findings that muscle aches and pains are reduced in pre–post testing, but does not mean that the risk of injury is decreased.
  • Sixth, some argue that stretching may prevent tendon or other injuries, even though there is no effect on total injuries. Finally, even if stretching does prevent one specific type of injury, because overall injury rates among stretchers and non-stretchers are not different, any protection against one type of injury would mean an increased risk of other types of injuries in order to balance the equation.

Based on his results, on can conclude that there are some conflicting results. Witvrouw et al point out that this:

can be explained by considering the type of sports activity in which an individual participates. Sports involving 'explosive' type skills, with many and maximal SSC (stretch-shortening cycles) movements require a muscle-tendon unit which is compliant enough to store and release the high amount of elastic energy. Recently, it has been shown that stretching is able to increase the compliance of human tendons, and as a result increase the capacity of the tendon to absorb energy. Consequently, in these sports we suggest that stretching is important as a prophylactic measure for injury prevention. When an individual's muscle-tendon unit is less flexible in these types of sports activities, there exists a predisposing factor for exercise-related injuries since the tendon is unable to absorb enough energy, which may lead to tendon and/or muscle damage. When the sports activity contains no, or only low SSC movements (cycling, jogging), all or most of the work is directly converted to external work. In these cases, there is no need for a compliant tendon since the amount of energy absorption remains low. Hence, additional stretching exercises to improve the compliance of the tendon may have no beneficial effect on injury prevention.

It must be acknowledged that the aetiology of injuries can be multifactorial. Taking out only one aspect (e.g. stretching) and examining its effect on the incidence of injuries is a rather narrow outlook on this problem. For example, fatigue is widely believed to be predisposing factor in muscle injury. In addition, other problems remain. Even within the same sport,the demands on different players may be different. However, we believe that far greater attention should be given to an examination of the type of activity in which the athlete participates when one considers the merits of stretching to reduce injury.

Now I can see you wonder: what if my workout require a large ROM?

To help you decide, here's a small anecdote from a professional dance trainer:

She is often shocked when she walks into dance studios to teach for the first time and sees dancers stretching on a cold floor. "I say, 'Please don't do that!' and explain that we'll stretch in the middle and at the end of class," she said. According to Solomon, stretching must be an integral part of the warm-up process. "As long as the blood is coursing through the body, the oxygen is flowing through the muscles, and the muscles are warm-then you can stretch," she said. "But not before. If you don't stretch and strengthen together, you'll have a weak muscle. The strength must balance the stretch if you want to control your movements." Solomon explained that dancers are at risk for injury partly because dance demands such extended ranges of motion. Moreover, ballet dancers typically do exercises such as developpes and grand battements that develop their quadriceps, but may neglect the hamstrings. The resulting strength imbalance puts extra stress on the knee joint. "If the muscles are really stretched out, the ligaments may not be able to protect the joints," she said. "So you get unstable joints, particularly knees, and you may get hyperextension and ligament tears." Proprioceptive neuromuscular facilitation stretches are now favored in the dance community because they both strengthen and lengthen muscles, Solomon said.

So what should you do?

Well the studies I reviewed concluded injuries occured in subjects with too much flexibility (lack of balance/strength) or a lack of flexibility (limited ROM). The latter group might consider increasing their ROM by stretching regularly (but not prior to exercising), however I would rather recommend you to perform workouts that let you make the desired motion naturally. You see, your body adapts itself to its needs, so instead of stretching to become more flexible stop working out so rigidly! Even worse, if you would stop stretching, you would loose all the gained flexibility because the body adapts itself to the lack of stretch.

To understand this, one must understand the way your muscles are built up. Your muscle consist of actin and myosin, which glide into one another during a contraction. These two parts optimize their length and overlap to get the highest force output. So if you start stretching your muscle, you require your muscle to adapt to retain an optimal overlap.

enter image description here

I expect you want to stretch after a workout because your muscles are still feeling contracted and by 'stretching' them, they'll be more relaxed. You know, yoga-style!

enter image description here

But if I show you this image and tell you that the mysion 'arms' require ATP (energy!) to release the actin, else they'd be holding on like rigor mortis. Furthermore, we just saw that your muscles probably have a lot of overlap and crossbridges, but you just depleted your energy resources, because you had an intensive workout. Do you think you're muscle will respond well to stretching?

Instead, I'd recommend you do a proper cooling-down, give your muscles time to get rid of lactate (which is a great resource of energy, when you burn it aerobically) and more importantly give it time to relax.

As a counterpoint, have a look at Kronos his answer at this question on Fitness.

References:

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Skeletal muscles have 3 "skills" or abilities that increase or decrease depending upon stress placed upon them: Strength, Endurance, and Flexibility. These 3 aspects work in a synergistic way to create movement. Stretching is an exercise that increases flexibility, so, just as you tailor your strength workout to meet strength goals any flexibility exercises should be tailored towards flexibility goals.

Delayed onset muscle soreness (DOMS) is a bit of a mystery, though it's rather intuitive. Soreness comes from damaged muscle tissues (ripped and shredded during exercise) and other wastes that have built up but not yet cleared. Cooling down is a great way to expedite removal of wastes. Once cooled down, further stretching can reteach the muscles to stay limber while removing the last bits of waste, allowing greater recovery and thus greater gains in your workout regimen.

A good rule of thumb is always stretch the muscles you worked, after cooling down but before too long. Not too much, just enough to feel it in the belly of the muscle that's now tired and growing sore long after your workout. The best thing to do is to treat flexibility as it is, a parameter of fitness, by staking out at least 1 day if not more solely for stretching. This will improve muscle health by most improving 1 of the three aspects of muscles fitness.

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Welcome to Skeptics! Please provide some references to support your claims. –  Oddthinking Mar 21 at 6:04

A couple of months ago, on NPR's Science Friday, they interviewed an exercise physiologist who was saying that current studies showed little if any actual benefit from stretching. Other than the fact that it felt pretty good....

No increase in range of motion, no decrease in muscle soreness, etc.

Unfortunately, I just did a search for the terms "exercise physiology" and "stretching" on the science friday site and got nothing.....

However, apparently it wasn't Science Friday. At least, this is a very similar article:

http://www.npr.org/templates/story/story.php?storyId=130509347

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