The five persistent myths of stretching.
One of the areas that persist with myths of practices from years gone by is that of stretching. Traditional stretching of muscles is not always had or even unnecessary, but the benefits and effects are not what you may think. New evidence in recent years is helping us determine the best time to stretch and techniques to use so that we can get the greatest value from the time invested.
So, first off, why do athletes stretch? The conventional wisdom says stretching is a necessary part of warm-up to help increase range of motion, decrease post-exercise soreness, decrease risk of injury, and increase performance (2). None, however, are proven benefits of stretching. Let's look at the research results found for each expected benefit.
Myth #1: Stretching lengthens muscles and increases the range of motion.
While there are many stretching techniques used in practice (e.g., static, ballistic, passive, PNF/proprioceptive neuromuscular facilitation), much of the research has looked at the most commonly used static stretching. The goal of static stretching is to put a muscle under tensile stress and hold the tension for a period of time so as to slowly lengthen the fibers and increase the range of motion around the joint over which the muscle crosses. The physiologic means by which this occurs is still not completely understood. The literature describes several viscoelastic properties of skeletal muscle (stress relaxation, creep, and hysteresis) that may explain increased sarcomere compliance and the lengthening process, but there is still some debate as to how much of the change is mechanical/structural and how much is functional/neurological (3), (4). It appears that initially much of the muscle lengthening is due to a decrease in the perceptible muscle tension as a result of an increase in stretch tolerance. As the discomfort of stretching decreases with time and repetition, the actin/myosin cross bridges are allowed to relax within their normal functional range for a period of time. This results in longer sarcomeres until the neurologic protective mechanisms kick in again to tighten and shorten the muscle fibers. This also explains why the increased range of motion (ROM) from stretching is usually short-lived. The typical routine of holding a stretch for 15 to 30 seconds increases range of motion for approximately only six to 90 minutes (5).
In order to affect the anatomic length of a healthy muscle over time, it is theorized that it must be stretched bevond the viscoelastic limits to initiate plastic change and create minor muscle damage. Therefore, longer duration stretching is required to have more prolonged effects. A minimum of four to five minutes of cumulative stretching for one muscle is needed to have lasting effects of more than a few minutes (4). In theory; an athlete who wishes to increase lower extremity ROM would need to spend at least 16 to 20 minutes per leg in daily stretching to increase flexibility in just the most commonly tight muscles (psoas, quadriceps, hamstrings, and gastrocnemius). Remodeling of tissue is time-dependent and requires consistency and frequency to affect lasting change. Consequently; the increased ROM obtained after six weeks of stretching may also be lost within just four weeks if not continued (6).
Some of the questions that still need to be answered with additional research are:
1) What creates the sense of "looseness" that most athletes experience after stretching? Is it the temporarily lengthened muscle? Is it the fascia or other connective tissue that becomes more flexible? Or is it the synovial fluid that becomes less viscous?
2) If increased range of motion is beneficial, what is the best means of improving flexibility? Is it static stretching or a different stretching technique such as post-isometric relaxation or contract-relax? Also, would the addition of manual therapy (e.g., myofascial release or joint manipulation) or specific exercise to correct a muscle imbalance achieve the best results?
One study by Fasen et al. found that hip flexion ROM was improved with hamstring stretching that created viscoelastic creep and decreased tension within the muscle. However, they also noted that results were improved with the addition of a neuromobilization technique, which demonstrated that flexibility is likely due not only to muscle, but also to nerve and/or connective tissue elasticity (6).
Join! manipulation is another technique that can create hoth an objective measurable increase in segmental flexibility and a subjective sense of looseness (7). Spinal manipulation has been shown to stimulate the muscle spindle and Golgi tendon organ afferents evoking paraspinal reflexes that can inhibit motorneuron excitability and, thus, relax skeletal muscle (8). Most of the joint manipulation research to date has looked at the spine, so it is not known how this may translate to the extremities. It is also not known how long the effect lasts or if it affects global range of motion.
Myth #2: Stretching decreases post-exercise muscle soreness.
Another reason athletes stretch is because they believe it helps to prevent or treat sore muscles. Post-exercise or delayed onset muscle soreness (DOMS) is problematic because pain impedes function. DOMS can develop shortly after exercise, last up to several days, and is usually experienced when an athlete trains or performs beyond their adapted fitness level. We have known for some time that the muscle soreness is not due to the build-up of lactic acid but, instead, due to inflammation or nociceptive pain resulting from micro-damage of the muscle.
Stretching has previously been thought to address the achy tightness associated with DOMS, however, this has not been shown in the literature to be effective. A recent Cochrane Review concluded that while one study demonstrated a 4% decrease in the severity of soreness, neither pre-exercise nor post-exercise stretching has any significant clinical impact on DOMS that would affect an athlete's function (2), (9).
There is some empirical evidence, however, that DOMS can be treated with massage or low intensity exercise, but this also needs further study. Massage does not remove lactic acid nor increase blood flow; but it can reduce inflammation. The only way to prevent DOMS is to limit the muscle damage in the first place by not stressing any muscle beyond its current functional capacity (10). But this advice, from a training perspective, would seem to also limit progressive improvement in fitness. Therefore, it is prudent to find the rate of progression in exercise that results in increased strength or endurance without causing significant muscle damage and inflammation that would lengthen recovery time and inhibit progress.
Myth #3: Stretching prevents injury.
Muscle strains are the most common sports injury and usually occur during an eccentric contraction when the actin-myosin filaments stretch and lengthen beyond their normal overlap within the sarcomere (11). Unfortunately, any evidence of stretching to prevent strains is once again disappointing. Numerous studies, including many of runners, looked at the relationship of stretching (mostly observing static stretching) and injury; and the majority concluded that pre-exercise stretching does not prevent muscle strains (3), (5), (11). However, there is little to no evidence showing an association between tendon, ligament, or other similar injuries.
Sluier previously outlined five theories as to why pre-exercise stretching does not prevent injury: 1) An increase in muscle compliance is associated with a decrease in the ability of the muscle to absorb energy during an eccentric load. 2) Muscle strain occurs within a normal range of motion; therefore, individual sarcomere length is related to injury, not the overall muscle length. 3) Injury occurs during activity and stretching does not affect active compliance of a muscle. 4) Over-stretching a muscle can cause damage by itself. 5) ROM increases due to stretch tolerance can mask the protective mechanisms of pain and result in increased injury risk (3).
There are again several gaps in the literature that must be considered. Does stretching post-exercise or on off-days decrease risk of injury? There is some evidence that prolonged periods of stretching can cause muscle fiber hypertrophy which may increase ability to absorb energy and, in theory; decrease injury risk (11), (12). However, it is not known if passive stretching of any duration outside of activity has any effect on reducing risk of injury (11).
What is the ideal ROM to decrease risk of injury? Prior studies have shown an association with extreme hypo- or hyper-flexibility and increased risk of injury, including overuse injury in runners, but optimal range of motion for decreased risk has not been well-defined (5), (13). And do different stretching techniques have different effects on injury risk? Again, there is little evidence to make an informed decision about technique because most studies have looked only at the relationship of static stretching and injury.
Lastly, subgroups of athletes may exist. Stretching and injury risk may be sport-specific, benefiting some athletes but not others. Injury risk may also be influenced by prior injury or susceptibility to injury.
Myth #4: Stretching improves performance.
Conventional wisdom used to support the concept that pre-exercise or event stretching increases ROM and flexibility and, thus, translates to improved speed or strength. We have already reviewed the evidence that stretching of modest duration only temporarily increases muscle length, but what is the subsequent effect on performance? There are again several factors we need to break down and look at separately.
The timing of stretching has now been shown to have very different effects on performance. Pre-exercise stretching causes micro-damage and decreased neurological reflex contraction, resulting in decreased muscular force, torque, and jumping ability (14). Therefore, it has been suggested that static stretching with holds greater than 25 seconds should be avoided before strength or power activities (15). Static stretching of 45 seconds (3 reps) has also been shown to decrease reaction time, movement time, and balance (16).
The decreased force production after stretching is believed to be due to decreased elastic energy on the muscle-tendon unit and decreased neural sensitivity of the muscle spindles. It is not known how long the effects of static stretching last but there is evidence showing it can decrease force output for up to two hours. This is due to neurological deficits and decreased muscle stiffness (17).
On the other hand, regular post-exercise or off-day stretching has been shown to increase force, torque, jumping, and sprinting performance. There is also evidence showing that regular stretching may cause muscle fiber hypertrophy and contribute to increased force/performance in the short and long term (14).
Another variable influencing stretching outcomes is the fact that different sports/athletes have different performance requirements. For example, less flexible distance runners have more economical biomechanics. That is. their oxygen uptake (V02) is less at a submaximal running speed. Less flexible muscles demand less energy because they use more elastic energy (40-50% of energy demand during distance running has been shown to be provided by elastic energy) (13). And lengthening a stiff muscle during running generates greater elastic tension, more so than that of a compliant muscle. On the other hand, pre-exercise stretching can increase running economy due to decreased viscoelastic muscle stiffness which then requires less energy to lengthen the muscle. This increased efficiency could improve long distance performance for endurance runners if the benefit lasted for more than a few minutes (14). But we must remember the fact that optimal ROM, or flexibility; of the lower extremities to maximize running economy is still not known (13).
Myth #5: Stretching is a warm-up.
Very simply, stretching does not equal a warm-up. The best approach to warming up and perhaps improving performance is, instead, dynamic movement to prepare the muscles and connective tissues for the intended activity. The warm-up should be designed to increase blood flow; increase speed of nerve impulses, increase oxygen flow and mechanical efficiency, and decrease muscle viscosity (5). It should also improve strength, body position awareness, and neuromuscular control.
For soccer, a sport that involves running, jumping, landing, and cutting, an appropriate warm-up has been shown to decrease lower extremity injury by one-third and severe injury by one-half (18). One study demonstrated decreased lower extremity injuries in female athletes that used a warm-up focused on balance, plyometric and agility exercises, and postural awareness (19). A neuromuscular warm-up may also improve joint position sense and joint stability develop protective joint reflexes, decrease non-contact knee injuries, and reduce overuse anterior knee pain (20).
In addition, several studies have concluded that static stretching should be avoided before practice or competition in favor of a gradual active dynamic warm-up (15), (21). An example of a dynamic warm-up would be that which starts with low intensity, small range of motion movements and progresses toward higher intensity, full range of motion movements required for that activity It is not known how long the dynamic stretch benefits last, so the warm-up should be performed close to the start of activity and each sport should be evaluated for the specific range of motion requirements for optimal performance (21).
Understandably, activities requiring large ranges of motion may require a much longer period of warm-up including both dynamic movement and stretching. For example, ballet dancers spend approximately 25% of their entire practice time on stretching. Static stretching is necessary to achieve the extreme ranges of motion required in that particular activity, but it is generally followed by a methodical dynamic warm-up that can offset the neural inhibition and strength loss of stretching alone (4).
Consequently, what can we conclude after reviewing the basic science and clinical application of stretching? Limited amounts of pre-exercise stretching can contribute to a feeling of looseness and short-term increased range of motion, but a significant amount of time needs to be committed to truly lengthen muscle. Only consistent and repetitive stretching with sufficient holds can have lasting impact on ROM. Also, pre-exercise static stretching does not reduce DOMS or risk of muscle strain injuries and can also impede performance for strength activities. On the other hand, a dynamic warm-up may decrease risk of injury and improve performance.
We must keep in mind that the ideal ROM for different sports activities is not known and specific stretching protocols for injury prevention and performance will differ between sports. For example, endurance sports such as long distance running and biking differ from power sports that involve jumping and/or sprinting. Also, activities that require upper extremity involvement (open kinetic chain movement) may differ from lower extremity activities such as running and jumping (closed kinetic chain movement). Spinal/trunk stretching and flexibility requirements may differ between activities, as well.
In summary, it can be recommended that pre-exercise or a pre-event dynamic warm-up is beneficial to feel limber, decrease risk of injury, and improve performance. However, pre-exercise or pre-event static stretching of more than 15 seconds per muscle should be avoided. If it is determined that increased ROM is required to improve function for a particular sport, then significant amounts of time need to be dedicated to stretching on off days to improve overall flexibility.
(1.) Committee on Quality of Health Care in America, Institute of Medicine. Crossing the Quality Chasm: A New Health System for the 21st Century (2001). Washington, DC: National Academies Press.
(2.) Jamtvedt G, et al. A pragmatic randomized trial of stretching before and alter physical activity to prevent injury and soreness. Br J Sports Med 2010; 44:1002-1009.
(3.) Shrier I. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science Literature. Clin J Sport Med. 1999; 9:221-227.
(4.) McHugh MR Cosgrave CM. To stretch or not to stretch: the role of stretching in injury prevention and performance. ScandJ MedSci Sports. 2010: 20:169-181.
(5.) Thacker SB. et al. The impact of stretching on sports injury risk: a systematic review of the literature. Med Sci Sports Exerc. 2004; 36(3):371-378.
(6.) Fasen JM, et ai. A randomized controlled trial of hamstring stretching: comparison of four techniques. J Strength Cond Res. 2009; 23(2):660-667.
(7.) Fritz JM. et ai. Preliminary investigation of the mechanisms underlying the effects of manipulation: exploration of a multivariate model including spinal stiffness, multifidus recruitment, and clinical findings. Spine. 2011; 36(21): 1772-81.
(8.) Pickar JG. Neurophysiologieal effects of spinal manipulation. Spine J. 2002: 2:357-371.
(9.) Herbert RD, el al. Stretching to prevent or reduce muscle soreness after exercise. Cochrane Database Syst Rev. 2011 ;7:CD004577.
(10.) Cheung K, Hume P. Maxwell 1.. Delayed onset muscle soreness: treatment strategies and performance factors. Sports Med. 2003; 33(2) : 145-64.
(11.) Weldon SM, Hill. RH. The efficacy of stretching for prevention of exercise-related injury: a systematic review of the literature. Man Ther. 2003; 8(3):l4l-l50.
(12.) Jenkins J, Beazell J. Flexibility for runners. Clin Sports Med. 2010; 29:365-377.
(13.) Trehearn TL, Buresh RJ. Sit-and-rcach flcxibilin-and running economy ol men and women collegiate distance runners. J Strength Cond Res. 2009; 23(1): 158-162.
(14.) Shrier I. Does stretching improve performance? A systematic and critical review of the literature. Clin J Sport Med. 200i; l4(5):267-273.
(15.) Hough PA, et al. Effects of dynamic and static stretching on vertical jump performance and electromyographic activity./Strength Cond Res. 2009; 23(2): 507-512.
(16.) Behm DG, et al. Effect of acute static stretching on force, balance, reaction time and movement time. Med Sci Sports Exerc. 2004; 36(8): 139-1402.
(17.) Power K. et al. An acute bout of static stretching: effects on force and jumping performance. Med Sci Sports Exerc. 2004; 36(8): 1389-1396.
(18.) Soligard T. et al. Comprehensive warm-up programme to prevent injuries in young female footballers: clustered randomized controlled trial. BMf. 2008; 337:a2469.
(19.) LaBella CR. et al. Effect of neuromuscular warm-up on injuries in female soccer and basketball athletes in urban public high schools. Arch Pediatr Adolesc Med. 2011: 165(11): 1033-1040.
(20.) Herman K. The effectiveness of neuromuscular warm-up strategies, that require no additional equipment, for preventing lower limb injuries during sports participation: a systematic review. BMC Med. 2012; 10:75.
(21.) Gergley JC. Acute effects of passive static stretching during warm-up and driver clubhead speed, distance, accuracy and consistent ball contact in young male competitive golfers. J Strength Cond Res. 2009; 23(3):863-867.
By Clifford W. Daub, DC
Dr. Daub is a chiropractic physician and Diplomate of the American Chiropractic Rehabilitation Board.
Stretching was a topic of interest at the AMM's 22nd Annual Sports Medicine Symposium at the Marine Corps Marathon[TM] and data from the 2011 USATF Stretch Study was presented by Daniel J. Pereles, MD. For more information on these study results, go to http://wwwMsatf.org/stretchstudy.
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|Author:||Daub, Clifford W.|
|Date:||Sep 22, 2013|
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