Stretching – Does it work?

Stretching: The Current Evidence

Sports practitioners, trainers, coaches and athletes have for decades routinely utilised stretching in pursuit of various fitness goals for recreational and elite athletes alike. But what are the evidence-based benefits of stretching? Do we advise and practice it out of habit, outdated beliefs or is it current best practice? This overview of the research on stretching should help to update your understanding of what works and why – as well as what doesn’t. It hopefully will go some way to help erode the infestation of dogma prevalent in local gyms and amateur sports clubs often through the ‘passing on’ of information by the more ‘set in their ways’ type members. The final point to consider is – why are you stretching? What are your aims and objectives from what is often quite aggressive way to manage your body?

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

The Basics

There are three commonly used stretching techniques:

  • Static: sustained pressure is applied to a muscle or muscle group in a lengthened position.
  • Dynamic or ballistic: repeated bouncing movements are made at the end of range of the muscle length, stimulating the stretching reflex.
  • PNF (Proprioceptive Neuromuscular Facilitation): combines a series of isometric muscle contractions and static stretches performed according to several specific protocols.

Stretching is normally done to try to achieve one or more of five aims:

1.     To increase muscle length

2.     To reduce the risk of injury

3.     To enhance prospects of healing for injured tissues

4.     To enhance performance

5.     To reduce pain associated with muscle and joint stiffness.

The many permutations of goals and techniques for stretching make it hard to draw overall conclusions from the research about what works in which circumstances. Below I have drawn out some of the main themes and conclusions – but it is clear that more research is needed in many areas (the role of stretching in flexion in lumbar spine flexibility/rehab, for instance, is relatively well covered and not prescribed whereas other muscle groups and other objectives are far less well researched).

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

Stretching for Flexibility

The research is quite varied in its support for the efficacy of the single most common use of stretching: static stretching to achieve an increase in range of movement (7,8). Increases in muscle length are thought to be achieved through two mechanisms (26):

1.     Increased muscle-tendon viscoelasticity results in a direct decrease in muscle stiffness (less force is needed to produce a change in muscle length).

2.     Inhibition (overcoming) of the stretching reflex reduces the active resistance of the muscle to the force applied.

How stretching is purported to work

Muscles (and their tendinous attachments) have properties of elasticity (resilience), plasticity (pliability) and viscosity (internal friction). Strength training over time generally bulks up and shortens the muscle; stretching lengthens it. The ‘stiffness’ of a muscle-tendon complex describes how readily it stretches when a given force is applied: a stiff muscle moves less far than a compliant one, which means it is less flexible, but on the other hand has greater potential elastic recoil and therefore stored power. The speed of movement also matters: the slower the loading, the more pliable and less resistant the quality of movement.

The muscle’s spindle cells govern the nervous system response to maintain contractile properties, most notably the ‘stretch reflex’ – the automatic contraction of a muscle, which has relaxed and lengthened to the edge of its safe range of movement. Stretching for flexibility was thought to use various slow, static and end-of-range movement techniques to overcome the stretching reflex and encourage a gradual lengthening of the muscle and tendon fibres and/or greater nervous system tolerance of the stretching at the end of range.

Unfortunately the current literature undermines some of our original postulations (as above) and suggests that for thousands of injured people and athletes looking to increase performance and treat injuries the outcomes may have been more injury promoting than either performance enhancing or rehabilitative (1,7,10). Basically it’s not as simple as we think.

Many instances of restricted range especially as the subject ages have been shown to be not founded in simple soft tissue restriction but due to adverse neural tension.

Research shows us that the dated concept of muscles just becoming ‘tight’ is not quite correct, experienced practitioners who keep up to date with current evidence now understand more of the soft malleable neural network of nerves that orchestrates the complexities of human movement, breathing, monitoring and reacting to probable injuries, controlling heart rate, thought, memory, energy/fuel delivery to organs and muscles, coordination, muscle contraction and kidney function to list but a few.

Consider the long term changes to the human spine due to work, physical exercise and stress. Picture for a minute the soft neural tissue being slowly compromised as it passes through the tightly packed anatomical pathways around the spine.  Now, make an educated guess at what would happen if this highly advanced calculating super-processor felt its own material might be injured or damaged encumbering the information super highway that actually manages your body every second of everyday.  Clearly, such an informed, hyper-advanced network would take action to impede this outcome.

The action?  Inhibition of further motion in the particular plane of movement that might cause or further the injury.  So is it ‘really’ spontaneous ‘tightness’ that most of us feel or the result of a highly evolved survival system making early educated decisions to reduce the probability of damage to the organism it’s tasked to keep alive – the human body?

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

In principle we previously suggested that stretching was an effective way of increasing muscle flexibility. Complicating factors are consideration of an appropriate exercise prescription. This is dependent on whether you are seeking short-term or long-term flexibility gains and of course why you would be seeking those changes in the first place.

Short-term gains were what we all expected when we undertook a conventional ‘preparatory’ stretching prior to activity, with the hope of enhancing performance or decreasing the risk of injury. However, numerous studies (20,23,24,26-29) suggest that a common side effect of static stretching is tendinous damage and confusion of our muscle spindles (our neurological feedback system or put another way the system that actually controls our movement). Long-term changes might be the goal during the management of a chronic injury, rehabilitation from an acute injury or to achieve a change in range of movement, which will facilitate an improved sporting technique that was previously inhibited by muscle inflexibility.

Magnusson (19) demonstrated in his 1998 study of passive properties of human skeletal muscle during stretching manoeuvres that long-term increases in joint range of motion resulted from a change in stretching tolerance rather than increased viscoelasticity. To complicate the picture further, different muscles have been shown to adapt differently to stretching and some muscle stretches may need to be held for longer than others.

In a 2004 literature review, Shrier and Gossal (25) suggested the following for static stretching flexibility protocols:

  • Static stretches should be held for 15 to 30 seconds.
  • Emphasize more coronal plate (rotational) stretches than sagittal (flexion and extension) (2, 7, 12, 16).
  • For short-term changes there is no benefit in holding a stretch for longer then 15 seconds and excessive force can promote injury (18).
  • There is no added benefit in repeating a stretch more than 4 to 5 times on one particular muscle (3, 10).

In a highly practical 1994 study, Bandy and Irion (2) looked at long-term flexibility changes. They found that muscles stretched for 30 seconds a day continued to yield gains in their range of movement for up to six weeks before the ROM reached a plateau. If the daily stretches were held for 15 seconds, it took 10 weeks to achieve the same degree of flexibility change. Stretching for greater ROM is more effective after a jogging warm-up (21, 29), and it is reasonable to suggest this would be true of other modalities of warm-up, too.

Importantly many studies support the change in muscle length due to stretching but also warn that many athletes post stretching programme are actually more inclined to injury (14, 20, 24, 25, 28). Stretching is more effective when heat or ice is applied (13), with heat having much the same effect as a warm-up and ice having an inhibitory effect or decreasing pain so as to enable greater stretch tolerance. Putting all these findings together, then, we can say that long-term isometric stretching programmes should produce changes in less than six weeks if stretches are done daily after a five-minute warm- up, held for 30 seconds and performed four to five times but that we need to understand despite the tissue changes the athlete is more prone to injury (14, 20, 24, 25, 28). All this said, not one of the above studies considered why we might want to elongate our muscular and ligamentous tissues, a question we should not take lightly!

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

PNF (Proprioceptive Neuromuscular Facilitation)

Research comparing the effectiveness of PNF stretching versus static stretching produces varied results. However, there seems to be consensus on the superior effectiveness of PNF stretching for increased flexibility, particularly with hamstring muscles.

Sady et al (1982) compared flexibility training using ballistic, static and PNF on shoulder, trunk and hamstring muscles and found PNF the most effective (24).  Etnyre and Abraham (1986) studied PNF versus static stretching on one-joint muscles using the plantarflexors of the ankle and reached the same conclusion (9). They also studied the two most common forms of PNF – contract-relax (CR) and contract-relax-antagonist-contract (CRAC) – and found the latter to be more effective. As sub maximal contractions during PNF are just as effective as maximal (11), it is advisable to use these, because of the lower risk involved. PNF stretching is equally effective whether contractions are held for three, six or 10 seconds (4).

Stretching to Reduce Injury Risk

The research evidence here is contradictory. It is also even harder to make valid comparisons between studies on this topic, as it splits between acute and chronic injury, as well as between the efficacy of stretching as part of an activity regime versus stretching regimes performed separately from any other workout.

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

Stretching & Activity

Two literature reviews shed some light on stretching in the context of activity, both pre-exercise and afterwards. In their 2004 review, Thacker et al (27), reported: ‘There is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes’ and called for more well-conducted randomised controlled trials. In 2002 Herbert and Gabriel (14), examined the hypothesis that ‘stretching before exercise does not seem to confer a practically useful reduction in the risk of injury’ and reported evidence to support that contention.

A study of military recruits between 1996 and 1998 who practised a series of 18 static stretches before and after training, compared to a control group who performed no stretches, demonstrated a significantly lower rate of muscle-related injuries in those who didn’t stretch, but no difference in the rate of bone or joint injuries (1). The way this study differentiates between different types of injury makes it exceptional among the research.

Stretching in Isolation

In the context of overall stretching programmes, a 2004 survey of flexibility training protocols and hamstring strains in professional football clubs in England conducted by Dadebo et (7) found that ‘hamstring stretching was the most important training factor associated with HSR [hamstring strain rate]’. The most common technique used was static stretching and the authors concluded that HSR went down in inverse relation to the amount of stretching incorporated into training. The less they stretched the less they were injured!

Turl and George (1998) reported something similar (28). They assessed rugby players with a history of repeated grade 1 hamstring strains versus a control group and found no variation in hamstring flexibility between the two groups. They also, however, found adverse neural tension in 57% of the hamstring injury group, against 0% for the controls. It is common to find a confused understanding of the difference between hamstring flexibility and adverse neural tension (restricted movement of a nerve as it passes along its tract) when stretching for increased flexibility is prescribed as part of a hamstring injury rehab programme.

We can summarise the knowledge on stretching to reduce injury risk thus:

  • It is proven that static stretches have a short-term beneficial effect on muscle stiffness and that muscle tone and flexibility can affect the movement of a joint.
  • An overall static stretching regime does little to reduce muscular injuries in fact it may promote injuries.
  • Performing static stretching before or after exercise does not prevent injury.

From these conclusions, it is reasonable to extrapolate that there are chronic injuries where excessive flexibility is an underlying cause of pain and in these cases stretching will often be detrimental. The role of stretching in chronic injury management is certainly an area needing more research.

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

Stretching for Injury Rehabilitation

The aim of stretching during rehabilitation is to aid extensibility of the healing site and return normal muscle length as early as possible. Malliaropoulos et al (2004) assessed the role of stretching during rehabilitation from grade II hamstring strains and concluded that the group ‘which carried out a more intensive stretching programme, was found to have a statistically significant shorter time of regaining normal ROM and rehabilitation period’ (20).

The importance of a controlled progression of stretching during rehabilitation from muscle strain is widely accepted and backed by the research. What is less clear is whether we should stretch injured muscle tissue in the same way as non-injured tissue. We also need more investigation into what role, if any, there is for ballistic stretching during rehabilitation.

Stretching for Increased Performance – To maximise power and safe joint control, don’t stretch!

Plenty of research data is available on this question. Most of it relates to the effect of preparatory static stretching on the performance of activities involving the stretch reflex or maximal voluntary contraction (MVC) – in other words, sports demanding explosive power such as sprint, high jump or basketball. Importantly what is also clear is the loss of muscular control over joint movement due to preparatory static stretching causing biomechanical movement faults (3, 7, 12, 17).

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

The Haka!  The ideal warm up?  Perhaps so…

Thus the balance of data finds that static stretching has a negative effect on the subsequent performance of activities involving the stretch reflex. Power et al (23) found that a preparatory bout of static stretching decreased the isometric force output of the quadriceps muscles for the next two hours. This would certainly suggest that for optimum performance in explosive sports, pre- activity stretching is not a good idea and that control (in this case) of the knee could be in question for runners.

In a separate 2005 study, Cramer et al (6) also demonstrated a decrease in force production and muscle activation in the rectus femoris and vastus lateralis muscles after static stretching. Notably both muscles cross the knee joint and have some responsibility for biomechanical control and therefore stability of the knee.

To put this decrease in force output into functional terms, we can refer to a 2004 study that assessed the effect of different static and dynamic stretching protocols on the 20m sprint performance of rugby union players (12).

The static stretching warm-ups resulted in a decrease in performance; whereas dynamic warm-ups improved performance. A dynamic stretching programme features e.g., swinging movements of the arms and legs that take activity-specific muscles through a range of movement, imparting a stretch at the end of range which is not held (also known as ‘elastic stretching’).

The authors speculate that the static stretching increases compliance within the muscle-tendon unit, which in turn reduces the unit’s capacity to store elastic energy. The beneficial response to a dynamic warm-up is thought to relate to the rehearsal of specific movement patterns, which may help increase the coordination of subsequent movement through the neural system.

In a study of the effect of static prep stretching on performance of vertical jump, Knudson et al (16) found detrimental affects on the kinematics of the vertical jump, and a decrease in vertical velocity in 55% of the subjects. They concluded that it is neuromuscular inhibition rather than reduced muscle stiffness after stretching that is responsible for the changes in performance.

Interestingly a 2003 study measuring the effect of static preparatory stretching on concentric isokinetic muscle action of biceps brachii, revealed the opposite (10), with no measurable change in EMG amplitude. The researchers suggested that deficits in force production after stretching were related to muscle stiffness changes rather than neuromuscular control.

So while it is reasonable to conclude that static stretching can have a negative impact on performance of activities involving the stretch reflex, maximal contractions and joint control, we cannot confidently say why.

What can we conclude about how static stretching influences other aspects of performance?

Nelson et al (22) demonstrated a significant reduction in muscle strength endurance after static muscle stretching.

Many sports, such as the tennis serve or golf swing, combine complex movement patterns with a need for maximum force and accuracy. Very little data seems to exist on how stretching might affect these activities – so this is another area ripe for further investigation. The best advice in practical terms is likely to be based on an extrapolation from tests involving simple movement tasks. Beyond this there seems to be just one study, Knudson et al (17), on the performance of a tennis serve after static stretching, which used speed of serve and accuracy as outcome measures. It demonstrated no change in performance.

Stretching to Reduce Pain

It doesn’t work on DOMS

It is a common belief that recreational athletes suffer with DOMS (delayed muscle onset soreness) because they fail to stretch sufficiently before activity; it is also said that DOMS can be alleviated with subsequent bouts of stretching. In reality DOMS is linked to an athlete’s physical ability to tolerate the eccentric loading of a particular activity and preparatory stretching cannot relieve this soreness (15). Neither stretch, cryotherapy nor electrotherapy has any effect in relieving DOMS (5). DOMS can only be relieved by NSAIDs, exercise and possibly massage.

More generally it is very hard to undertake objective assessment of the benefits of stretching in reducing injury-related pain. If an injury is associated with a restriction in muscle flexibility, then stretching is a viable treatment option. However, if muscle inflexibility is not considered an influencing factor, for example in the much more common presentation of an instability problem, then clinical reasoning should rule out stretching as a treatment tool. Thus the use of stretch is going to be determined by the specific individual’s injury profile.

In Summary

Sports therapists and other health professionals lack a harmonised ‘best practice’ approach to stretching based on the available research. This ‘head in the sand’ approach creates a lower level of service for the paying public. Further, the author suggests that there is simply far too much anecdotal hearsay amongst local clubs and sometimes professional clubs.

Here’s what do actually we know:

Stretching for knee pain, stretching for back pain, stretching for neck pain, stretching for hamstring injury, stretching for sports injury, stretching for back injury, stretching for sports

  • Static stretches with the aim of achieving short-term range-of-movement gains should be held for 15 to 30 seconds and for maximum effect should be repeated four to five times. These short-term changes will last between 60 and 120 minutes. Importantly they are likely to predispose the athlete to injury.
  • For long-term changes, stretches should be held for 30 seconds and also repeated four to five times. Long-term results should take six to seven weeks at most before the changes start to plateau. Athletes that have undergone this type of regime have been found to illustrate reduced biomechanical control.
  • PNF can achieve range of movement changes, and is often more affective then static stretching, but is also more difficult for athletes to perform on their own.
  • It is reasonable to assume that PNF techniques will achieve the same results as those produced by the various research studies into static stretching.
  • Stretching is a vital part of recovery from muscle strains and a progressive stretching programme can decrease rehabilitation time.
  • Preparatory stretching will not prevent injury. However, from practical experience, it is the author’s belief that specific static prep stretches can be beneficial in the management of chronic injuries.
  • A regular stretching routine as part of an overall training programme does not prevent injuries.
  • Static stretching should not be included in warm-ups, as it seems to decrease performance of explosive actions, biomechanical control of joints under load and activities demanding muscle strength endurance.
  • Soft tissues do not spontaneously become tight, there is a complex interrelation with the neurological system and its management of our body.
  • Do you actually need to stretch Do you actually need to stretch? Consider the rational, what exactly is a tight hamstring for example?
  • Is your therapist just using a ‘shotgun’ approach to your health?

We are still some way from having a clear picture of the pros and cons of stretching. However, there is still solid evidence from which we can draw conclusions and base our management and training programmes. In many cases, the research challenges traditional approaches, which underlines the importance of sports practitioners and athletes keeping up to date with the science, so they can adjust their practice and programming in line with the best available evidence, not, the anecdotal ‘it worked for me’ mentality or the one size fits all physical practitioner which is currently so common.

References

1.     Amako M, Oda T, Masuoka K, Yokoi H, Campisi P: Effect of static stretching on prevention of injuries for military recruits. Mil Med. 2003 Jun;168(6):442-6

2.     Bandy WD, Irion JM: The effect of time on static stretch on the flexibility of the hamstring muscles. Phys Ther 1994:74(9):845-852

3.     Bennell K, Tully E, Harvey N: Does the toe-touch test predict hamstring injury in Australian Rules footballers? Aust J Physiother. 1999;45(2):103-109

4.     Bonnar BP, Deivert RG, Gould TE: The relationship between isometric contraction durations during hold-relax stretching and improvement of hamstring flexibility. J Sports Med Phys Fitness. 2004 Sep;44(3):258-61

5.     Cheung K, Hume P, Maxwell L: Delayed onset muscle soreness : treatment strategies and performance factors. Sports Med. 2003;33(2):145-64

6.     Cramer JT, Housh TJ, Weir JP, Johnson GO, Coburn JW, Beck TW: The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography. Eur J Appl Physiol. 2005 Mar;93(5-6):530-9. Epub 2004 Dec 15

7.     Dadebo B, White J, George KP: A survey of flexibility training protocols and hamstring strains in professional football clubs in England. Br J Sports Med. 2004 Aug;38(4):388-94

8.     Davis DS, Ashby PE, McCale KL, McQuain JA, Wine JM: The effectiveness of 3 stretching techniques on hamstring flexibility using consistent stretching parameters. J Strength Cond Res. 2005 Feb;19(1):27-32

9.     Etnyre BR, Abraham LD: Gains in range of ankle dorsiflexion using three popular stretching techniques. Am J Phys Med. 1986 Aug;65(4):189-96

10. Evetovich TK, Nauman NJ, Conley DS, Todd JB: Effect of static stretching of the biceps brachii on torque, electromyography, and mechanomyography during concentric isokinetic muscle actions. J Strength Cond Res. 2003 Aug;17(3):484-8

11. Feland JB, Marin HN: Effect of submaximal contraction intensity in contract-relax proprioceptive neuromuscular facilitation stretching. Br J Sports Med. 2004 Aug;38(4):E18

12. Fletcher IM, Jones B: The effect of different warm-up stretch protocols on 20 meter sprint performance in trained rugby union players. J Strength Cond Res. 2004 Nov;18(4):885-8

13. Henricson AS, Fredriksson K, Persson I, et al: The effect of heat and stretching on the range of hip motion. J Orthop Sports Phys Ther 1984:110-115

14. Herbert RD, Gabriel M: Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. BMJ. 2002 Aug 31;325(7362):468

15. Johansson PH, Lindstrom L, Sundelin G, Lindstrom B: The effects of preexercise stretching on muscular soreness, tenderness and force loss following heavy eccentric exercise. Scand J Med Sci Sports. 1999 Aug;9(4):219-25

16. Knudson D, Bennett K, Corn R, Leick D, Smith C: Acute effects of stretching are not evident in the kinematics of the vertical jump. J Strength Cond Res. 2001 Feb;15(1):98-101

17. Knudson DV, Noffal GJ, Bahamonde RE, Bauer JA, Blackwell JR: Stretching has no effect on tennis serve performance. J Strength Cond Res. 2004 Aug;18(3):654-6

18. Magnusson SP, Simonsen EB, Aagaard P, et al: Biomechanial responses to repeated stretches in human hamstring muscle in vivo. Am J Sports Med 1996;24(5):622-628

19. Magnusson SP: Passive properties of human skeletal muscle during stretch maneuvers. A review. Scand J Med Sci Sports. 1998 Apr;8(2):65-77

20. Malliaropoulos N, Papalexandris S, Papalada A, Papacostas E: The role of stretching in rehabilitation of hamstring injuries: 80 athletes follow-up. Med Sci Sports Exerc. 2004 May;36(5):756-9

21. McNair PJ, Stanley SN: Effect of passive stretching and jogging on the series elastic muscle stiffness and range of motion of the ankle joint. Br J Sports Med1996;30(4):313-318

22. Nelson AG, Kokkonen J, Arnall DA: Acute muscle stretching inhibits muscle strength endurance performance. J Strength Cond Res. 2005 May;19(2):338-43

23. Power K, Behm D, Cahill F, Carroll M, Young W: An acute bout of static stretching: effects on force and jumping performance. Med Sci Sports Exerc.2004 Aug;36(8):1389-96

24. Sady SP, Wortman M, Blanke D: Flexibility training: ballistic, static or proprioceptive neuromuscular facilitation? Arch Phys Med Rehabil. 1982 Jun;63(6):261-3

25. Shrier I: Does stretching improve performance?: a systematic and critical review of the literature. Clin J Sport Med. 2004 Sep;14(5):267-73

26. Shrier I, Gossal K: Myths and Truths of Stretching: individualized recommendations for healthy muscles. The Physician and Sports Medicine 2000 Aug. 28(8)

27. Thacker SB, Gilchrist J, Stroup DF, Kimsey CD Jr: The impact of stretching on sports injury risk: a systematic review of the literature. Med Sci Sports Exerc. 2004 Mar;36(3):371-8

28. Turl SE, George KP: Adverse neural tension: a factor in repetitive hamstring strain? J Orthop Sports Phys Ther. 1998 Jan;27(1):16-21

29. Verrall GM, Slavotinek JP, Barnes PG: The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian Rules football players. Br J Sports Med. 2005 Jun;39(6):363-8

Comments are closed.