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Overview
This is what the evidence says:
Hamstring stretches of between 30-60 seconds once a day will increase flexibility in uninjured muscles over a 6 week period.
Single 15 second stretches are sufficient to increase the flexibility of adductor muscles in men.
Carrying out a single 20 second stretch pre-exercise will not prevent injuries in Army recruits.
PNF stretching is more effective than static stretches for improving the flexbility of the hamstrings and quadriceps muscles
Static stretching before exercising for runners increases the risk of injury.
Stretching the hamstrings after vigorous running (70% max HR) is more effective than stretching “cold”
Elite swimmers have greater flexibility ratings than non-athletes.
Excessive flexibility of the shoulder joint can be a source of pain for swimmers.
Insufficient flexibility of the shoulder joint can cause impingement of the rotator cuff in swimmers.
Stretching for 20 seconds before or after exercise does not affect muscle soreness in Army recruits.
Jogging and running is more effective at increasing the flexibility of the plantar-flexors than static stretching from cold in uninjured muscles.
Increasing flexibility does not reduce running economy for a 10 minute sub-maximal run on a treadmill.
In sub-elite distance runners, a degree of inflexibility of the hip rotators and ankle dorsiflexion results in an increase in running economy.
An increase in the flexibility of the hamstring muscle group reduces the risk of injury in runners.
Stretching for between 15 and 30 seconds is sufficient for most people, to gain an increase in flexibility.
What is my professional opinion / advice?
If you are naturally quite flexible, then you don’t need to do loads of stretching. 10-15 second holds x3 will suffice post exercise. If you are very stiff / inflexible, then you need to pay more attention to stretching. 30sec’s – 2 mins x3 post exercise. If you are middle of the road, keep it this way. 20-30 second x3 post exercise.
For Triathlon, stretching pre exercise is not required. however, a good warm up with dynamic movements / mobilisations is. eg, leg swings / arm circles, drills, etc etc. finish you’re work out, stretch briefly and re-fuel. Then 30 mins, stretch again, holding the stretches longer this time.
If you have been injured / recovering from injury, often some hands on soft tissue work will aid you in the recovery of normal tissue flexibility. ie. massage.
Disclaimer… this is no substitute for seeing a sports physio / sports doc / experienced sports therapist / or coach, and getting your individual needs addressed, everyone is different. Previous injuries and biomechanical differences will require individualised approaches to your stretching regime.
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Introduction
The medical literature is very confusing on this matter, and often contradictory in nature and that most of the theoretical and practical factors in stretching are often incorrectly applied. The aim of this article is to summarise what we know, how the current literature should be interpreted and thus what the current recommendations are. The critical reviews are discussed and specifically relevant studies are critically appraised. The evidence is then summarised and recommendations made for further research.
There is a commom sense that flexibility is relevant for top sports performance and that stretching is carried out to maintain or promote flexibility. Most coaches, athletes and medical professionals use stretching as an integral part of the training process, irrespective of which sport they partake in. However, the relevance of flexibility may vary among different sports. If this assumption is correct, not only the magnitude of body flexibility, but also data variability will be inversely related to the relevance of flexibility for a given sport (Araújo, 1986).
It is generally accepted that increasing the flexibility of a muscle-tendon unit promotes better performances and decreases the number of injuries (Witvrouw et. al. 2004). From the basic science research, we find that an increase in tissue compliance due to temperature, immobilization, or fatigue is associated with a decreased ability to absorb energy (Shrier 2001). Although increased compliance is not the equivalent of stretching, no basic science research shows that an increase in compliance is associated with a greater ability to absorb energy. Stretching exercises are regularly included in warm-up and cooling-down exercises; however, contradictory findings have been reported in the literature (Thacker et. al. 2004). Several authors have suggested that stretching has a beneficial effect on injury prevention. In contrast, clinical evidence suggesting that stretching before exercise does not prevent injuries has also been reported. Apparently, no scientifically based prescription for stretching exercises exists and no conclusive statements can be made about the relationship of stretching and athletic injuries. Stretching recommendations are clouded by misconceptions and conflicting research reports. Although some of the references used here are a little dated, it should be remembered that article searches should not be limited to specific time periods, as many “pearls of wisdom may be untouched” (Ellis, R. 2007). Where possible, older references are supported with updated reviews.
What is Flexibility?
Flexibility is a measure of the ability of the muscle tendon units to elongate within the physical restrictions of the joint. Therefore, flexibility of a joint is affected by the nature of the joint structure, the condition of the ligaments and fascia that surrounds the joint, and muscle extensibility. It can also be limited by the skin, connective tissue, and bones around the joint (Kent 1994). It should be noted that flexibility is joint specific. Just because someone can touch their toes, does not mean that they can reach round and scratch their back if the shoulders have poor flexibility. Therefore, no single flexibility test can be used to evaluate whole body flexibility (ACSM 2000p86). It is also sports specific, a front row rugby player is going to have different flexibility properties to that of an Olympic gymnast, if the rugby player were to have those levels of flexibility they would highly detrimental to their sporting performance. Any research into the effect of stretching can thus only be applied to the client group investigated. Many authors tend to relate flexibility solely to a muscle group, however, in healthy subjects, it is more likely that biochemical alterations in collagen and elastin structure account for variation among individuals in flexibility. As we age, the connective tissue becomes less extensible, and there is a resulting loss in flexibility. Although some people are described as “loose jointed” there is little aggreement on the difinition and limits of normal flexbility (Thacker et al. 2004). When carrying out a stretch, the unit of concern is often the muscle tendon unit and specifically the passive elements of that unit which are the connective tissues comprising of collagen fibres. Maintenance of any increase in ROM after the stretch has been performed is due to the influence of creep on the connective tissues. However, the duration of the ideal stretch has not been identified (Walker, J. 1994).
There are three main types of stretching exercises which are used in an attempt to increase flexibility (Thacker et al. 2004). Static stretching, ballistic stretching, and proprioceptive neuromuscular facilitation (PNF). Static stretching is a method whereby the muscle is slowly elongated to tolerance and the position held with the muscle in this greatest tolerated length (ACSM 2000). This is either done passively by a partner, or by the individual themselves. The ballistic method uses bouncing or jerking movements, which can theoretically exceed the extensibility limits of the muscle in an uncontrolled manner and thus cause injury. For this reason, it is not widely supported in the literature (Anderson and Burke 1991, Bandy and Irions 1994, ACSM 2000p158). PNF techniques utilise contract-relax, or hold-relax, involving either an isometric contraction of the muscle to be stretched prior to a static stretch being administered, or a contraction of the antagonistic muscle prior to the passive stretch. Studies assessing the effect of stretching have used various techniques, and various lengths of time the stretch is held for and the number of repetitions. For this reason, it is often difficult to compare findings between different studies.
Hypermobility syndrome
The hypermobility syndrome (HMS), also known as congenital laxity of ligaments and joints, occurs as an isolated condition. It is measured by assessing joint hypermobility at three or more locations (greater than or equal to 5 points on a 9 point Beighton scale). Although joint hypermobility is relatively common in the general population, reports of musculoskeletal complaints are infrequent. There remains debate about the exact nature of the condition, it’s impact, and any relevant treatment (Grahame and Bird 2001). This condition is often not identified due to doctors, physiotherapists, and other professionals being trained to identify a loss of flexibility (Grahame 1990). One reason is that it has been given relatively little attention in the literature. Most reports are in the rheumatology literature, with virtually none in the orthopedic or physical therapy literature. However, it is worth noting that it exists and can result in various muscluloskeletal conditions. HMS has been reported in 0.6% to 31.5% of adults without joint pain, depending on age, ethnicity, and criteria for assessing hypermobility (Finsterbush and Pogrund 1982). It is also more prevalent in females than males (Russek 1999). The treatment recommended is exercise to develop protective reflex reactions and to strengthen the surrounding musculature.
In patients with HMS, it has been suggested that there is alteration of proprioceptive acuity. Hall et al. (1995) studied the proprioceptive performance of the knee joint in 10 female subjects. Their findings suggest that hypermobile subjects have poorer proprioceptive feedback than controls. Reduced sensory feedback may lead to biomechanically unsound limb positions being adopted. Such a mechanism may allow acceleration of degenerative joint conditions, and other musculoskeletal complaints. For example, lightweight women rowers who had excessive spinal mobility were more likely to have back problems if they participated in a stretching program for their backs (Howell 1994). It appears reasonable, therefore, to advise individuals with HMS to use stretching exercises cautiously, distinguishing between stretching muscles and stretching joints, as the former may be beneficial but the latter may be harmful (Russek 1999).
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What happens in Hypomobility / loss of flexibility?
Loss of flexibility, or muscle extensibility, leads to a variety of alternations in locomotor system function, none of which is ordinarily beneficial (Tunnell 1998). Hypomobility, increased compressive force and non-physiological loading may arise within joints crossed by the shortened muscle, and this relentless pull of short muscles on sensitive structures can cause pain, may set the stage for later degenerative changes in the joints, or develop tendonopathies at the insertions (Gunn et al. 2007). Antagonists of a shortened muscle may be reciprocally inhibited or may be required to generate greater force than usual to achieve intended movements. The change in length-tension relationships, can result in the muscle no longer being able to develop peak tension and thus “tight weakness” develops (Grossman et al. 1982) Altered movement patterns readily develop as muscles that should normally be silent or only synergistic for an intended movement are recruited. Painful trigger points can then develop in the overactivated muscles (Simmons et al. 1999). Shortening of the para-spinal muscles acting across joint spaces can compress the disc and cause narrowing of the intervertebral foramina, and can indirectly irritate the nerve root through pressure of a bulging disc, or by direct pressure on the nerve root after it emerges (Gunn et al. 2007). Lack of flexibility in the lower back and posterior thigh is also associated with chronic low back pain (ACSM 2000p157). The shortened muscle itself is a source of altered proprioceptive information to the central nervous system, which bases its’ instructions for movement and posture upon afferent signals from the peripheral structures, namely the muscles and joints, by affecting the neuropathways and impulse transmission. There can therefore be changes to postural alignment and alterations to the alignment of the centre of gravity and line of gravity. Tight muscles will offer more resistance to movement, and thus require more energy for the movement to be executed (Dintiman 1964). In triathlon, athletes undergo large physiological, biomechanical and sensori-motor adjustment during the cycle to run transition (Millet and Vleck 2006). Thus, through both mechanical and neurological means, even a non-painful shortened muscle can exert a far reaching influence on overall locomotor function. It is therefore essential to regard any muscle shortness as a significant problem which must be addressed. However, it must also be noted that a lack of flexibility, despite being responsible for numerous injuries, does not account for many muscle injuries which occur during normal ranges of movement (Thacker et al. 2004). Most muscle injuries are believed to occur during eccentric contractions, which can cause damage within the normal range of motion because of heterogeneity of sarcomere lengths (Shrier 2001). Therefore, if injuries usually occur within the normal range of motion, why would an increased range of motion prevent injuries?
Since triathlon is an endurance sport, with high numbers of swimming strokes, pedal cycles, and running strides, any small biomechanical inefficiency can soon lead to injury once many thousands of repetitions are encountered. Although there are a number of other causes of overuse injuries, inflexible muscles is one of the key reasons athletes get injured (Hellemans J.), but as noted, one must not stretch muscles indiscriminately. Because if there is a benign hypermobility, stretching could cause injuries.
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Evidence base for stretching
Before we take a close look at that investigation and several other key studies on stretching, we should bear in mind that stretching research has traditionally fallen into two key categories: (1) randomized, controlled trials, and (2) cohort studies. In the former, the somewhat uniform individuals taking part in the study are randomly divided into two groups, and one group then stretches regularly as a normal part of training while the other group goes does no stretching. This is actually the best way to get a feeling for stretchings’ efficacy, because it tends to eliminate various forms of bias which could significantly distort the results of the research.
Cohort studies are usually easier to carry out, however, and as a result they appear much more often in the scientific literature. In cohort-style research, scientists would simply follow athletes who routinely do or do not stretch over time to determine which group had a higher incidence of injury. Naturally, such cohort investigations are susceptible to considerable bias. Although some authors argue that only research from randomized clinical trials (RCTs) of humans should be used to determine clinical management (Jadad 1998) an alternative is to consider the study design (eg, RCT, cohort, basic science) as one of many variables, and that no evidence should be discarded a priori. The careful interpretation of all evidence is, and has always been, the real art of medicine (Shrier 2001).
There are a number of problems other than bias, with Cohort studies, summed up by Anderson’s article on pponline.co.uk. For example, studies that found that stretchers and non-stretchers had similar injury rates, it might be because stretching was ineffective as an injury-prevention technique, but it might also be true that stretching actually lowered injury rates in ‘tight’ football players who sensed they needed stretching, making their injury rates comparable with the flexible people who didn’t feel a need to stretch. And if non-stretchers had a lower frequency of injury, you might conclude that stretching actually increased the chance of muscle trauma, but it might also be the case that the timing of stretching was wrong, an improper form of stretching was utilized, or that stretching did lower injury rates – but not enough to make stretchers as injury-resistant as the naturally lax athletes (an easy-to-see bias in these cohort studies is that many individuals who stretch probably do so for a reason – because their muscles are unusually tight; individuals who don’t routinely stretch may avoid stretching because they are naturally flexible, and it may be these intrinsic factors (tightness and flexibility) which ultimately determine injury rates, not the selection or avoidance of stretching). An additional worrisome factor is that athletes might have been somewhat dishonest about their stretching habits (since you had undertaken a cohort study and had no direct control over how the athletes actually stretched and trained, there would be little way of knowing whether the players were actually doing what they said they were doing). If enough athletes distorted their stretching habits, your results would also be distorted.
Thacker et al. (2004) produced a systematic review of the literature surrounding stretching and injury prevention. The meta-analysis was limited to randomized trials or cohort studies for interventions that included stretching. Studies were excluded that lacked controls, in which stretching could not be assessed independently, or where studies did not include subjects in sporting or fitness activities. All articles were screened initially by one author. Six of 361 identified articles compared stretching with other methods to prevent injury. Stretching was not significantly associated with a reduction in total injuries and similar findings were seen in the subgroup analyses. However, they acknowledged that many of the studies they used had methodological problems, which were complicated by both ascertainment and information biases, lacking in sufficient statistical power and having inadequate control of any potentially confounding variables such as a warm up. They also recognised that the majority of the studies were carried out on runners. They therefore concluded that there is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes.
Shrier (2004) carried out a systematic review of the literature on stretching and sporting performance. He examined 23 articles on the effects of an acute bout of stretching, 22 articles suggested that there was no benefit for the outcomes isometric force, isokinetic torque, or jumping height. There was 1 article that suggested improved running economy. Of 4 articles examining running speed, 1 suggested that stretching was beneficial, 1 suggested that it was detrimental, and 2 had equivocal results. Of the 9 studies examining the effects of regular stretching, 7 suggested that it was beneficial, and the 2 showing no effect examined only the performance test of running economy. There were none that suggested that it was detrimental. He concluded that an acute bout of stretching does not improve force or jump height, and the results for running speed are contradictory. Regular stretching improves force, jump height, and speed, although there is no evidence that it improves running economy. Reasons put forward were, that even mild stretching can cause damage at the cytoskeletal level, and that stretching some-how increases tolerance to pain, that is, it has an analgesic effect which could therefore lead the individual more susceptible to injury. Also that the preparation for athletic activites often include both stretching and a warm up, which makes it difficult to assess the independent effects of each on injury prevention.
Swimmers with reduced flexibility, or with strength imbalances, either avoid the shoulder positions and movement patterns which promote a technically efficient stroke, or they achieve the correct stroke pattern by compensating with undesirable movement of the shoulder joint putting it in a position that may cause impingement (McLean, B. ?)
Ozcaldiran (2002) investigated the relationship between static flexibility of shoulder and shoulder pain in swimmers compared to controls. In order to evaluate the role of the flexibility on shoulder pain in swimmers, 42 competitive age group elite swimmers and 31 age and gender matched nonathletic controls were enrolled in the study. A significant increase in total flexibility index was seen in swimmers. However, swimmers who had shoulder pain had higher value of total flexibility index than those who had no shoulder pain. There was a statistically significant positive correlation between the total flexibility index and shoulder pain in both dominant and nondominant shoulder of the swimmers. These findings suggested that excessive shoulder flexibility in swimmers may be one cause of shoulder pain in the swimming athlete, although a certain level of flexibility is required for an efficient stroke.
Pope et. al. (2000) investigated the effect of muscle stretching during warm-up on the risk of exercise-related injury. They used 1538 male army recruits who were randomly allocated to stretch or control groups. During the 12 wk of training, both groups performed active warm-up exercises before physical training sessions. In addition, the stretch group performed one 20 second static stretch under supervision for each of six major leg muscle groups during every warm-up. The control group did not stretch. 333 lower-limb injuries were recorded during the training period, including 214 soft-tissue injuries. There were 158 injuries in the stretch group and 175 in the control group. There was no significant effect of preexercise stretching on all-injuries risk, soft-tissue injury risk, or bone injury risk. Fitness (20-m progressive shuttle run test score), age, and enlistment date all significantly predicted injury risk (P < 0.01 for each), but height, weight, and body mass index did not. Therefore they concluded that a typical muscle stretching protocol of 20 seconds performed during pre-exercise warm-ups does not produce clinically meaningful reductions in risk of exercise-related injury in army recruits.
However, scientific research does not universally support the idea that more than 20 seconds are required to loosen up particular muscle groups. For example, in classic scientific research carried out at the Stanford University School of Medicine, 72 men were randomly divided into four groups: Members of one group statically stretched their hip adductors for 15 seconds at a time, individuals in a second group stretched for 45 seconds, and men in a third group stretched their adductors for two minutes at a time, a fourth, non-stretching group served as a control. As it turned out, there was ultimately no difference in hip-adductor flexibility between the groups, i.e., 15 seconds of stretching was just as effective as two minutes, in terms of increasing the flexibility of the adductor muscles (Madding et al. 1987).
Bandy and Irion (1994) studied the length of time the hamstring muscles should be placed in a sustained stretched position to maximally increase ROM. Fifty-seven subjects (40 men, 17 women), ranging in age from 21 to 37 years and with limited hamstring muscle flexibility, 30 degrees loss of knee extension measured with femur held at 90 degrees of hip flexion, were randomly assigned to one of four groups. Three groups stretched 5 days per week for 15, 30, and 60 seconds, respectively. The fourth group, which served as a control group, did not stretch. The data analysis revealed a significant group x test interaction, indicating that the change in flexibility was dependent on the duration of stretching. Further post hoc analysis revealed that 30 and 60 seconds of stretching were more effective at increasing flexibility of the hamstring muscles (as determined by increased ROM of knee extension) than stretching for 15 seconds or no stretching. Although, no significant difference existed between stretching for 30 seconds and for 1 minute, indicating that 30 seconds of stretching the hamstring muscles was as effective as the longer duration of 1 minute. They therefore suggested that stretching for 15 seconds or less was effectively a waste of time as minimal increases in flexibility were likely to occur. However, this contradicts the findings of Madding et al. (1987) who found that a 15 second stretch was as effective as a 2 minute stretch for increasing the flexibility of the hip adductor’s. It should be noted that the difference between Madding et al. (1987) and Bandy and Irions’ (1994) study is that Madding et al. only looked at the effect of one episode of stretching, which is unlikely to provide a true indication of what actually occurs to gain long term increases in flexibility, compared with Bandy and Irions who carried out a 6 week study. Given the information that no increase in flexibility of the hamstring muscles occurred by increasing the duration of stretching from 30 to 60 seconds, the use of the longer duration of stretching for an acute effect must be questioned, due to the minimal further increases in flexibility. Bandy and Irions’ (1994) acknowledged that their study was limited to assessing the effects of one session of static stretching per day, and that further research is needed to evaluate the effects of different duration so stretching performed at various times during the day. Clincially, those with pathologically short muscles are advised to stretch between 3 and 5 times a day, yet the evidence is lacking to support these recommendations. This study was assessing the effect of stretching on healthy individuals, it would therefore be useful to repeat the study with a clinical sample with individuals with a reduced ROM due to a muscle pathology, to determine whether similar results in terms of time are obtained. The authors did not identify whether the subjects were stretching completely cold, or whether they had “warmed up” in any way prior to the stretching episode, which is common practice. Although the implication is that they carried out the stretching “cold”. It would again be useful to repeat the study but carry out the stretching after an bout of exercise to assess any differences between pre and post exercise stretching.
Shrier and Gossal (2000) reviewed the literature on stretching and range-of-motion increases and found that one static stretch of 15 to 30 seconds per day is sufficient for most patients, but some require longer durations. Heat and ice improve the effectiveness of static stretching only if applied during the stretch. But concluded that an individualized approach may be most effective based on intersubject variation and differences between healthy and injured tissues.
Hreljac et al. (2000) looked at biomechanical and anthropometric variables that could contribute to overuse injuries in runners. Comparisons were made between a group of runners who had sustained at least one overuse running injury and a group of runners who had been injury free throughout their running careers. Groups were well matched in important training variables. Synchronized kinetic and rearfoot kinematic variables of both feet were collected by filming subjects running over a force platform. The injury-free group demonstrated significantly greater posterior thigh (hamstring) flexibility, as measured by a standard sit and reach test. This was the only anthropometric variable in which the groups differed. Within each group, there were no significant differences between left and right foot landing for any biomechanical variable. Biomechanical variables that demonstrated significantly lower values for the injury free group were the vertical force impact peak and the maximal vertical loading rate, with the maximal rate of rearfoot pronation and the touchdown supination angle showing a trend toward being greater in the injury free group.
Craib et al. (1996) examined the association between nine measures of limb and trunk flexibility and running economy of 19 well-trained male sub-elite distance runners. Correlational analyses revealed that dorsiflexion and standing hip rotation were significantly associated with the mean aerobic demand of running. Thus, runners who were less flexible on these measures were more economical. Although speculative, these results suggest that inflexibility in certain areas of the musculoskeletal system may enhance running economy in sub-elite male runners by increasing storage and return of elastic energy and minimizing the need for muscle-stabilizing activity. Since stretching exercises have been shown to increase joint range of motion, stretching exercises may be contraindicated for endurance running performance.
However, Nelson et al. (2001) investigated the influence of a 10-week program of stretching exercises on the oxygen costs of a 10 min sub-maximal (approx. 70% peak VO2) treadmill run. Thirty-two (16 female, 16 male) physically active, treadmill accommodated, college students participated in the study. All participants maintained their current activity level, with half the participants (8 female, 8 male) adding a 40 min, 3 days per week session of thigh and calf muscle stretching exercises. After 10 weeks, the stretching group exhibited a significant increase in the sit-and-reach, while the non-stretching group experienced no significant change. However, neither the streching group nor the non stretching group exhibited a significant change in the O2 cost for the submaximal run. Therefore, Nelson et al. (2001) concluded that a chronic stretching program does not necessarily negatively influence running economy.
McNair and Stanley (1996) carried out a studdy to determine the effect of stretching and jogging on the series elastic muscle stiffness of the plantar flexors and on the range of dorsiflexion at the ankle joint. 24 healthy subjects participated in this study. Each subject undertook all of the following protocols, in random order: (1) stretching protocol: five 30 s static stretches with 30 s rest between stretches; (2) aerobic jogging protocol: subjects ran on a treadmill for 10 min at 60% of their maximum age predicted heart rate; (3) combined protocol: subjects ran first and then stretched. A damped oscillation technique was used to measure the series elastic stiffness of the plantar flexors. Dorsiflexion of the ankle was assessed with a weights and pulley system that moved the ankle joint from a neutral position into dorsiflexion passively. Electromyography was used to monitor the activity of the plantar and dorsiflexors during these procedures. The statistical analysis of these data involved an analysis of covariance. They found that for decreasing series elastic muscle stiffness, running was more effective than stretching. In contrast, the results for range of motion showed that the combination protocol and the stretching only protocol was more effective than the running only protocol for increasing the dorsiflexion range of motion at the ankle.
Herbert and Gabriel (2002) carried out a systematic review to determine the effects of stretching before and after exercising on muscle soreness after exercise, risk of injury, and athletic performance. Of the randomized controlled trials, only five met their criteria and concluded that stretching before or after exercising does not confer protection from muscle soreness. Stretching before exercising does not seem to confer a practically useful reduction in the risk of injury, but the generality of this finding needs testing. Insufficient research has been done with which to determine the effects of stretching on sporting performance. The bulk of their conclusions were drawn from the Australian miltary studies (Pope et al. 2000) as discussed above. An important limitation of their study was the inclusion of articles only written in English, which may result in bias in the conclusions. Another limiting factor is their inclusion of both randomized and quasi randomized studies in the systematic review. By doing this, the authors may have confounded their ability to reduce bias and random error among the included studies. This potential confounding could be detrimental to the strength of the evidence reported in the review. However, this observation is likely most important for the muscle-soreness component of the review, as the injury-risk component included only randomized studies. Because these investigators only studied army recruits, the authors stated it would be interesting to assess the effect of more prolonged stretching performed by recreational athletes over an extended time (ie, months or years) on injury risk reduction.
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Although investigating stretching in athletes over a prolonged period would seem to be the next logical step in the study of stretching and injury risk reduction, some insights from Shrier (1999) suggest otherwise. That is, during his review of the basic science literature, he noted 5 theoretic arguments against pre-exercise stretching for injury prevention. One argument deals with the concept of compliance in muscles (ie, the length change of a muscle when force is applied). As seen in the basic science literature, increased muscle compliance is associated with a decreased ability to absorb energy in a muscle at rest, whereas a contracting muscle is less compliant but can absorb more force. Therefore, greater compliance, which can be achieved through stretching, is not necessarily related to the tissue’s resistance to injury. A second concept presented is related to the observation that sarcomere length in an active muscle is heterogeneous. This is significant during muscle activity because when some sarcomeres are stretched to the point that the actin and myosin filaments do not overlap, the force being absorbed is transmitted to the muscle fiber cytoskeleton, resulting in fiber damage. In addition, the basic science literature indicates these events can happen when the joint is within its normal range of motion. Therefore, muscle compliance may be irrelevant to injury, whereas loss of energy-absorbing capacity of overstretched sarcomeres is of greater importance.
Recent studies have shown that stretching programmes can significantly influence the viscosity of the tendon and make it significantly more compliant, and when a sport demands SSCs of high intensity, stretching may be important for injury prevention. This conjecture is in agreement with the available scientific clinical evidence from these types of sports activities. In contrast, when the type of sports activity contains low-intensity, or limited SSCs (e.g. jogging, cycling and swimming) there is no need for a very compliant muscle-tendon unit since most of its power generation is a consequence of active (contractile) muscle work that needs to be directly transferred (by the tendon) to the articular system to generate motion. Therefore, stretching (and thus making the tendon more compliant) may not be advantageous. This conjecture is supported by the literature, where strong evidence exists that stretching has no beneficial effect on injury prevention in these sports. If this point of view is used when examining research findings concerning stretching and injuries, the reasons for the contrasting findings in the literature are in many instances resolved.
In a study carried out at James Madison University in Virginia, 12 healthy subjects tried out four different hamstring- stretching protocols: ( I ) after running at a fast-enough speed so that heart rate stayed above 70 per cent of heart-rate reserve for four minutes or more (heart-rate reserve is simply max heart rate minus resting heart rate), (2) after running at just 60 per cent of heart-rate reserve for three or more minutes, (3) after warming up the hamstring muscles with heating pads, (4) with the muscles in a ‘cold’ state – after no warm-up running or heat-pad application.
Stretching the hamstrings after vigorous running (at 70 per cent of heart-rate reserve or above) proved to be far superior to the other three methods at promoting hamstring flexibility. In fact, the range of motion at the hip was 5 per cent higher when stretches were carried out after vigorous running, compared to either light running or the application of heating pads. In addition, flexibility was nearly 10 per cent greater after strenuous running, compared with stretching muscles in the ‘cold’ condition.
The stretches carried out by the James Madison athletes were the ‘PNF’ (proprioceptive neuromuscular facilitation) type, meaning that stretches of the hamstrings were alternated with contractions of the same muscles. Both the stretch and contraction period lasted for about 10 seconds, and each stretch and contraction of the hamstrings was repeated three times. The stretch- contractions were carried out one, five, 10 and 15 minutes after exercise or the application of heat pads, but no additional gains in flexibility were made beyond the one-minute period
Interestingly enough, stretching the muscles in the cold condition didn’t help improve flexibility at all, yet countless numbers of athletes stretch their sinews before their training sessions. In addition to the promotion of greater flexibility, another advantage associated with stretching AFTER working out, not before, is that it may speed recovery. A large number of studies carried out in the medical field have shown that stretching stimulates the passage of amino acids into muscle cells, accelerates protein synthesis inside the cells, and inhibits protein degradation. Thus, post-workout stretching should help muscle cells repair themselves and synthesise energy-producing enzymes and structures which enhance overall fitness.
The improvement in flexibility and potential augmentation of recovery which are noted when stretching occurs after a vigorous workout may help to explain the findings of David A. Lally, Ph.D., an exercise physiologist at the University of Hawaii-Manoa who carefully studied 1543 participants in the Honolulu Marathon. Lally found that runners who stretched after their workouts had relatively low rates of injury, compared to runners who didn’t stretch, while runners who stretched BEFORE training sessions had HIGHER rates of injury.
Although this study seems shocking at first glance, since its results suggest that the conventional practice of stretching before workouts may be doing more harm than good, the research is not so surprising when examined carefully. First, remember that one goal of stretching is to improve flexibility, and we’ve already seen (from the James Madison study) that stretching muscles before a workout, when they are ‘cold,’ doesn’t always improve flexibility, while stretching the sinews after a workout makes them more like elastic rubber bands. Second, bear in mind that although it’s popular to position stretching before the beginning of a workout, there’s actually very little resemblance between the act of stretching out a muscle and the rapid shortenings (contractions) which muscles undergo during a typical workout. In other words, stretching doesn’t represent specific preparation for an actual training session. During a stretch, a muscle is elongated and then held in a static position; in a workout, a muscle shortens repeatedly.
On the other hand, muscles are often fairly tight – and in some cases close to going into a spasm – after a very strenuous workout ends. At that point, stretching is a fine way to transform a hypercontracted muscle into a relaxed collection of fibres which can comfortably adapt to the more passive activities which usually follow a training session. As mentioned, post-workout stretching may also be a fine way to help muscles recover in time for a subsequent quality- workout.
Many different stretching techniques are available to athletes, but research carried out at the University of North Texas supports the idea that PNF stretching (the type used in the James Madison study) is superior to regular passive stretches at unkinking muscles and expanding joint flexibility (Research Quarterly for Exercise and Sport, vol. 63(3), pp. 311-314,1992).
In the Texas study, 120 college students were randomly assigned to receive one of four different stretching treatments, all of which were designed to lengthen the hamstring muscles in the posterior, upper portion of the leg. The treatments involved:
( I ) Regular passive stretching, in which the investigators manually flexed the legs of the students at their hip joints until tension or discomfort was felt behind the knee
(2) A passive stretch of the hamstrings (as above) followed by an ‘active’ stretch of the hamstrings which was the result of a strong contraction of the quadriceps muscles in the front of the thigh. After the active stretch, there was another passive stretch of the hamstrings. (3) A passive stretch of the hamstrings, followed by a three-second isometric contraction of the hamstrings, an active contraction of the quadriceps muscles, and then a passive stretch of the hamstrings. (4) The same as no. 3, except that the three-second isometric contraction involved the quadriceps, not the hamstrings.
Treatments 2-4 all can be classified as PNF stretches, because relaxation of the hamstrings is ‘facilitated’ by various nerve-muscle reflexes which are activated by muscle contractions (in this case by contractions of the hamstrings or quadriceps). For example, when the quadriceps contract, reflexes automatically ‘tell’ the hamstrings to relax so that the quadriceps can carry out their task of flexing the leg at the hip without too much resistance from the hamstrings . Also, when the hamstrings themselves contract vigorously (as in the isometric contraction of treatment no. 3), other reflexes signal the hamstrings to relax and loosen up a little.
The North Texas study is supported by research carried out at the famed Karolinska Institute in Stockholm, Sweden. There, scientists were able to to improve the muscle flexibility of 47 athletes (runners, orienteers, soccer players, and ice-hockey participants) by about 6 to 10 per cent by using ‘contract-relax’ (PNF) stretching for the calf, thigh, and hamstring muscles. The PNF stretches were carried out quite easily: individual muscles were stretched for about eight seconds, contracted for eight seconds, and then stretched again for eight seconds. This sequence was repeated five times per training session per muscle group, with great results.
So what should you do before your workout begins? Instead of stretching, try other, more specific preparatory activities. Walking, jogging slowly, skipping, hopping, walking on toes (with toes pointed to the inside, straight ahead, and to the outside), walking on heels (ditto). But don’t throw away stretching altogether. You can complete your PNF stretching routine when your workout is over. After all, it’s easy ! Just remember to stretch each important muscle group for eight to 10 seconds, contract it for about the same amount of time, and then stretch it for eight to 10 more seconds. Do this three to five times for each muscle group after a workout, and in short order you’ll be much more flexible. (Bledsoe,J online)
Much of medicine in general, and sport medicine in particular, is based on historical precedent. When historical precedents are based solely on hypotheses that have more recently been proved incorrect, clinicians must choose to continue treatment on the basis of a known incorrect idea of pathophysiology or change to a treatment based on current knowledge of pathophysiology and pathobiology. The potential side effects of any new treatment (likely to be unknown) must also be weighed against the potential side effects of the historical treatment (more likely to be known). The art, and even science, of medicine then becomes the ability to weigh all the available information at hand without discriminating a priori, and to be able to judge which is most appropriate for the patient (Shrier 2001).
It has therefore been suggested by a number of authors that part of these contradictions can be explained by considering the type of sports activity in which an individual is participating. Sports involving bouncing and jumping activities with a high intensity of stretch-shortening cycles (SSCs) [e.g. soccer and football] require a muscle-tendon unit that is compliant enough to store and release the high amount of elastic energy that benefits performance in such sports. If the participants of these sports have an insufficient compliant muscle-tendon unit, the demands in energy absorption and release may rapidly exceed the capacity of the muscle-tendon unit. This may lead to an increased risk for injury of this structure. Consequently, the rationale for injury prevention in these sports is to increase the compliance of the muscle-tendon unit.
Another reason to carry out a stretching program is to reduce the risk of exercise associated muscle cramping (EAMC). Latest research in this area has suggested that EAMC is a result of an abnormality of sustained alpha motor neuron activity which stems from aberrant control at the spinal level (Schwellnus 1999). The central factor is muscle fatigue that causes lack of control through an excitatory effect on the muscle spindle afferent activity and an inhibitory effect on the type Ib Golgi tendon organ afferent activity. An epidemiologic study of 1300 marathon runners by Manjra et al. (1996) identified risk factors for EAMC including older age, longer history of running, higher body mass index, shorter daily stretching time, irregular stretching habits, and family history of cramping. Poor stretching habits appear to increase the risk for EAMC, as they could lead to an exaggerated myotonic reflex, thereby increasing spindle activity (Schwellnus 1999).
Conclusion
In summary, the results of this review do not support the role of pre-exercise or postexercise stretching as an intervention addressing postexercise muscle soreness. In addition, the evidence presented in this review does not support the role of pre-exercise stretching in the reduction of lower extremity injury risk. However, it should be understood that we need further studies of stronger methodologic quality and studies that focus on other regions of the body as well as on the lower extremity. We also need further study of the longitudinal application of stretching and injury risk reduction
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Tim Pigott - Health and Performance 3 