Debunking common stretching myths
This title may appear to be a dumb question to some. Stretching is a natural part of all exercise. We stretch during gym class, before starting a group run, information during football practice. Heck, if don’t stretch we will never get the fancy Presidential Fitness bumper stickers for our parents.
As a physical therapist, I was taught stretching in graduate school and I routinely witness stretching in the clinic. But history and anecdotal evidence do not answer the question. Should you stretch before athletic events? Is flexibility important? Should therapists prescribe it to their patients?
These are not simple yes or no answers. The evidence is not clear, but neither were my questions. Stretching does not have a single goal. Justification for its use include injury prevention, improving mobility, a warm-up prior to physical activity, pain reduction, pleasure, enhancing strength and performance gains, and general health. The effectiveness of stretching differs depending on the end goal. Allow me to break it down.
Stretching for injury prevention
Despite the current evidence, the idea stretching prevents injury — even enhances performance — is taught as a common fact; suggesting otherwise is met with incredulity. Every kid growing up in organized sports has experienced lining up and running through the series of stretches comprising the majority of a warm-up. The act of stretching prior to activity has been passed down as common knowledge for generations. It spreads beyond organized sports as well. Running groups everywhere start their morning runs with a stretch of the quadriceps, hamstrings, adductions, and gastrocnemius. Yet, it is likely they were not reducing their risk for injury or physically preparing for the run.
If your coach’s sage wisdom and anecdotal experiences are weighing heavily on you, allow me to provide some clarity. The evidence is mixed but heavily leans towards no effect.
Krivickas, 1996, Arch Phys Med Rehabil 
No relation between muscle tightness and injury was found for women; however, for men, there was a significant relationship between increased muscle tightness and incidence of lower extremity injury in general and, more specifically, between increased iliopsoas tightness and overuse knee injury.
Twellaar, 1997, Int J Sports Med 
No significant differences in terms of ROM about the ankle, hip, and knee between physical education students who sustained lower extremity injuries and those who did not
Shrier, 1999, Clin J Sports Med 
The basic science literature supports the epidemiologic evidence that stretching before exercise does not reduce the risk of injury.
Pope, 2000, Med Sci Sports Exerc 
A typical muscle stretching protocol performed during pre-exercise warm-ups does not produce clinically meaningful reductions in the risk of exercise-related injury in army recruits.
McKay, 2001, BJSM 
Elite and recreational basketball players who did not stretch during warm-up were at a significantly increased risk of injury compared with those who did stretch.
Soderman, 2001, Knee Surg Sports Traumatol Arthrosc 
Knee hyperextension greater than 10° was a risk factor for lower extremity injury in female soccer; however, ankle dorsiflexion ROM and hamstring flexibility were not risk-factors.
Herbert, 2002, BMJ 
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
Hart, 2005, Clin J Sports Med 
Limited evidence showed stretching had no effect in reducing injuries.
Brushøj, 2008, Am J Sports Med 
An exercise program with an emphasis on muscular strengthening, coordination, and flexibility based on intrinsic risk factors identified through a literature review did not influence the risk of developing overuse knee injuries or medial tibial stress syndrome in subjects undergoing an increase in physical activity.
Kay, 2011, Med Sci Sports Exerc 
The detrimental effects of static stretch are mainly limited to longer durations (≥ 60 s), which may not be typically used during pre-exercise routines in clinical, healthy, or athletic populations. Shorter durations of stretch (<60 s) can be performed in a pre-exercise routine without compromising maximal muscle performance.
This is not a comprehensive list, but when breaking down stretching into categories we see a significant thinning of the number of studies. In our world of rehabilitation, stretching is often studied with respect to treatment. Patients will, however, discuss stretching for preventing a flare-up of symptoms or re-injury. The current evidence does not support its use in that capacity. If stretching achieves one of its primary underlying goals – improving mobility – we still don’t see a benefit.
Notice how a few of the studies referenced mobility rather than stretching. You will find studies that demonstrate an association between an increased range of motion – primarily assessing at the ankle and hip – and reduced incidence of injury. However, many of these are small effect sizes and lack controls. Taking a pool of data and looking for relationships afterward will reveal something (this brings us back to issues with observational and epidemiologic literature). Without repeatable results in new data sets, the information carries little weight. With poor repeatability and inconsistency between studies, we can hardly conclude a causative effect.
It is important to delineate the differences in how studies draw their conclusions. Some show associations between range of motion and injuries while others will evaluate the effectiveness of a specific stretching program. These are not the same thing. As we will assess in greater detail later, stretching does provide two benefits: a short-term, immediate, small increase in range of motion and an enjoyable sensation.. If you feel stiff and some stretching after lying on the couch all morning brings relief, by all means, stretch away. Stretching is not an act that warrants outlawing, but we should avoid claiming it prevents injuries or improves athletic performance.
Stretching as a warmup
We must answer three questions in this section: what is a warm-up, do warm-ups work in general, is stretching an effective warm-up? Like stretching before every soccer and football practice, physical therapists have been prescribing warm-ups prior to the start of their session for decades. You could argue a warm-up has many of the same goals I listed for stretching: injury prevention, improving mobility, pain reduction and pleasure, compounding strength, and performance gains. When assessing the research, warm-ups appear to be effective in many different areas.
The goal of a warm-up is to increase muscle temperature and prepare the body for the demands of the specific activity to be performed at moderate and high intensity while maintaining high-energy phosphate bioavailability. McGowan et al. published a review article on the mechanisms and applications of warm-ups in 2015. They concluded the following:
Passive and active warm-ups markedly influence subsequent exercise performance via increases in adenosine triphosphate turnover, muscle crossbridge cycling rate and oxygen uptake kinetics, which enhance muscular function. An active warm-up, consisting of a brief (<15 min) aerobic portion and completion of 4–5 activation sprints/race-pace efforts, post-activation potentiation exercises or small-sided games, elicits improvements in performance. Passive heat maintenance techniques can preserve the beneficial temperature effects induced via active warm-up during lengthy transition phases.
A passive warm-up — such as a hot shower or using heated garments — only provides benefits for about 15–20 minutes, indicating a need to immediately perform the intended activity. Note, hot packs do not achieve this benefit as they insufficiently warm the body.
Overall, the evidence points to the need for a warm-up to include dynamic activity and be of adequate duration and intensity to create a genuine “warming up” of the muscles. Furthermore, sport or activity specific activity appears to be necessary to maximize the effects on performance and injury prevention.
The McGowan review excluded studies evaluating static stretching as a sole warm-up but did state stretching “is known to impair subsequent performance.” They withheld reviewing static stretching and cited a 1994 JOSTPT review article by Craig Smith as their reasoning. In his review article, Smith concluded that static stretching should be integrated into a rehabilitation routine. The conclusion carries many caveats, however.
In all the studies singled out by Smith, regarding warm-up strategies for injury prevention and improving performance, they were multimodal. They all combined active and passive warm-ups and treatments. Many of them also compared two interventions rather than an intervention to a control. These major methodological weaknesses limit the ability to conclude stretching is an effective method for warm-up. But, again, we must be clear on the goals of the warm-up. A review by Wood et al. in Sports Medicine concluded stretching is effective for short term improvements in flexibility, but it revealed potential detriments to power performance. Many of the studies evaluating stretching and warm-up relate to the lower body. Do the conclusions differ when evaluating the upper extremities? They do not.
In a systematic review published in 2015 by the British Journal of Sports Medicine, McCrary et al. concluded the following:
Strong research-based evidence was found for the following: high-load dynamic warm-ups enhance power and strength performance; warm-up swings with a standard weight baseball bat are most effective for enhancing bat speed; short-duration static stretching warm-up has no effect on power outcomes; and passive heating/cooling is a largely ineffective warm-up mode.14
Overall, the evidence points to the need for a warm-up to include dynamic activity and be of adequate duration and intensity to create a genuine “warming up” of the muscles. Furthermore, sport or activity specific activity appears to be necessary to maximize the effects on performance and injury prevention.
But what about dynamic stretching? I would argue you are no longer stretching. Repeated movements, especially when they replicate the soon-to-be performed physical activity, are a type of mobilization. The repeated muscular contraction ramps metabolic activity and generates heat. This heat contributes to tissue adaptations such as increase muscle extensibility and thus becomes a dynamic warm-up. Research supports dynamic warm-ups for enhancing performance and minimizing injury occurrence. But the benefits are enhanced when the warm-ups are tasks specific. Dynamic “stretching” may be best served at the beginning of a warm-up, but then a transition to tasks specific movement is needed.
One of the more popular and evidence-backed warm-up routines was designed as an injury prevention strategy. The “11+” program – sometimes called the FIFA 11 – has demonstrated favorable injury prevention results when the compliance is high. The 20-minute warm-up consists of two stages of running exercises and a stage of strength, plyometric and balance exercises in between. No stretching in sight. How does this compare to our clinic warm-ups?
While a stationary bike or incline treadmill walking will be superior to static stretching, it is hardly an optimal modality for preparing the body for moderate or high-intensity activity. Furthermore, it is a simple movement in the sagittal plane. Even if you prescribe lateral and reverse walking on the treadmill, there is little variation in speed, amplitude, and effort. We want to prepare our patients for the movements and exercises we are going to ask them to perform in the clinic. If the session calls for 3 sets of 8 standing mid rows at 95 pounds of resistance, then an appropriate warm-up could be 4 sets of 5 repetitions of gradually increasing weight to prepare for the more intense sets. Implementing a type of coordination exercise prior to return to sport type movements may be a beneficial add as well.
In conclusion, static stretching is not supported as an effective strategy for warming up, and it may even be hinder athletic performance.
How about treatment?
This is the moment many of you have all been waiting for. Should we prescribe stretching as a treatment intervention? There are two primary areas we need to evaluate here as well. Does stretching facilitate healing and do the expected benefits of stretching, primarily greater flexibility, improve function and performance.
Overall, the evidence does not support stretching as an effective means to improve performance; it may even worsen it. Stretching does provide some short-term flexibility improvements, which we will explore further, but are they necessary?
First, let’s explore the impact of stretching on flexibility. Weppler and Magnusson provide some insight in their paper Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation?
Studies that evaluated the biomechanical effect of stretching showed that muscle length does increase during stretch application due to the viscoelastic properties of muscle. However, this length increase is transient, its magnitude and duration being dependent upon the duration and type of stretching applied. Most of these studies suggest that increases in muscle extensibility observed after a single stretching session and after short-term (3- to 8-week) stretching programs are due to modified sensation. The biomechanical effects of long-term (>8 weeks) and chronic stretching programs have not yet been evaluated.
The study explores various theories for why flexibility may increase following stretching. They specifically look at muscle extensibility and the torque/angle curves. After a robust literature review, they conclude many of the theories are not supported by the evidence. Viscoelastic deformation suggests “when a stretch is applied to a muscle and the muscle is held in the stretched position for a period of time, as is the case with normal static stretching techniques, the muscle’s resistance to stretch gradually declines. Constant load stretching, such as stretching that uses a fixed torque, can be used to evaluate the property of creep. Creep occurs when mechanical length gradually increases in response to a constant stretching force.” Unfortunately, studies evaluating this phenomenon show the deformation to be transient in nature, with the effect lasting as little as 30 seconds.
One of the more commonly referred to models is plastic deformation. This model suggests that a stretch of sufficient intensity can “pull connective tissue within the muscle past the elastic limit and into the plastic region of the torque/angle curve so that once the stretching force is removed, the muscle would not return to its original length but would remain permanently in a lengthened state.” None of the 10 studies assessed that evaluate this claim, however, supported the model.
Another popular theory is stretching creates an increase in sarcomere in series. This is one of the primary theories underlying serial casting. While the increased sarcomeres have been observed in animal models, the length of each sarcomere shortens, canceling out the increase in number. There is no observable overall change in muscle length. Due to the nature of this model, it cannot be tested in human subjects and remains primarily theoretical.
Lastly, before addressing sensation, we have the neuromuscular relaxation model. The model theorizes that to increase muscle extensibility, using a slowly applied static stretch will stimulate neuromuscular reflexes to induce relaxation of the targeted muscles. Like the previous theories, when tested in experimental studies, the results failed to show any effects.
This brings us to sensory theory. It argues that “increases in muscle extensibility observed immediately after stretching and after short-term (3- to 8-week) stretching programs are due to an alteration of sensation only and not to an increase in muscle length.” The individual conducting the stretch simply tolerates greater torque application rather than experiencing a mechanical change. The sensory perception change results in increases in the end-range joint angle without a shift in passive torque/ankle curves. Unfortunately, longer-term stretching programs (>8 weeks) have not assessed the effect on passive torque/angle curves.
Stretching is not the only way to improve flexibility
It is important to note some key areas not addressed. Stretching is not applied in a universal manner. We must consider the duration, torque, and mode of stretching. We must also consider patient characteristics such as irritability, sensitivity to stretching, and belief in its effectiveness. Take a study conducted by Guissard and Duchateau. In their 2004 study published in Muscle & Nerve, they observed a right shift of torque/angle curves, not only a sensation change, over a 6-week training period. To achieve the outcomes, subjects performed 20 minutes of ankle plantar-flexor stretching 5 days a week; far more than the traditional 15-150 second holds you typically find in literature. We must then ask ourselves, what is the dosage of the stretch, and if the patient requires 20 minutes of stretching, is that the best use of time? Contrary to popular opinion, stretching is not the only method to improve mobility
Research has demonstrated strength training through a full range of motion, without the inclusion of stretching, improving sit and reach scores 10-25%.[18-22] The ability for strength training to improve mobility has been demonstrated in the literature for 75 years.  We see similar benefits following aerobic training but the evidence is more sparse and the studies are multimodal rather than exclusively assessing aerobic training. Regardless of the method, it appears dynamic exercise yields positive mobility benefits across all ages and fitness levels. We still haven’t answered the primary question though. Is increased flexibility necessary? To an extent.
Is flexibility important?
In PT school, we learned about the necessary range of motion thresholds for functional tasks, such as the amount of knee flexion and ankle dorsiflexion necessary to descend stairs. While these thresholds are needed for ‘normal’ movement patterns, they are not strictly necessary to perform a task. If you can only flex a knee to 90 degrees, you are not doomed to a life of avoiding stairs. If you are only able to flex your shoulder to 90 degrees, you will still manage to wash your hair. Our bodies are remarkably resilient and adaptive. We develop new movement patterns through new neural connections and altered connective tissue, whether it be hypertrophy, muscle extensibility changes, or bone structure adaptations. Yes, some compensatory movement patterns may result in pain or risk for injury, but it is far from a guarantee.
The danger setting a range of motion standard – the within normal or functional limits designations – is we ignore differing anatomy and physiology. Baseball pitchers will differ in shoulder rotation bilaterally due to connective tissue adaptations resulting from repeated throwing, including humeral retroversion – a twisting of the bone. Hip mobility may differ from side to side because of different levels of femoral ante or retroversion. Squat mechanics differ between someone 5’8” and someone 6’8” because of differing proportions of their femur and tibia lengths relative to their trunk. Spinal mobility will decrease with age or history of trauma without concurrent pain or function changes. None of these changes will alter a patient’s life, but they will stand out during an examination. Furthermore, many of the findings are either optimal (the baseball player) or unable to change (the squatters). What mobility ‘restrictions’ should we be concerned about?
Much debate is had over this question. Some of the debate is a result of the significance bias. During examinations, we search for a cause of the patient’s symptoms. Often times we attribute the first clinical finding that is plausible as the root cause; especially if we can create a change with our treatment. We must ask ourselves, however, if treating the finding is necessary. Some of the classic reasons for treating poor mobility, such as the dreaded upper and lower cross syndrome, fail when applied to the rigors of controlled research. The old adage of weak and lengthened muscles creating an imbalance with related strong and tight muscle is primarily observational and anecdotal. The foundation of the postural model as a whole is crumbling. Furthermore, clinicians can’t agree on the definitions of tight, lengthened, weak, and strong.
What about facilitating tissue recovery? When treating an injury undergoing remodeling and repair, stiffness is desired. Our nervous system intentionally inhibits contractility to protect the damaged tissue. Blowing through the restrictions to achieve an arbitrary range of motion goals will only lead to harm. Neural tissue, especially, should not be trifled with. When elongation exceeds 5% strain, conduction block occurs. Rupture of neural tissue can occur with less than 10% strain.
How about DOMS? Once again, the evidence does not support stretching as an effective strategy.[25-27] Clearly, there must be some witnessed benefits. What are the effects clinicians achieve that warrants continued use of stretching?
Some studies do demonstrate a positive impact on recovery. For example, a 2004 study in Sports Medicine divided 80 Greek athletes with grade 2 hamstring strains into two groups.28 The groups were evaluated and began treatment within 48 hours of injury. During the first 48 hours, all participants were treated with the P.R.I.C.E. (protection, rest, ice, compression, elevation) protocol. Following the re-evaluation of the injury, they were randomly assigned to one of two groups. Both groups completed 30-second static stretches of the hamstrings. The only difference between the two groups was the number of stretching sessions, 4 versus 1. What did they find?
Group B, which carried out a more intensive stretching program, was found to have a statistically significant shorter time of regaining normal ROM (5.57 +/- 0.71 d) and rehabilitation period (13.27 +/- 0.71 d) in comparison with group A (7.32 +/- 0.525 d and 15.05 +/- 0.81 d, respectively).
While a 36-hour return to sport is not irrelevant, it is a small difference. The study lacks a key group, however. Without a control group who did not receive any stretching intervention, we cannot know whether the stretching was the differentiating factor. We also lack control of any other activity the participants performed or the influence of lifestyle factors such as sleep and nutrition. We find similar issues in other studies.
It is important to remember the concept of the ‘burden of proof.’ If someone is making a claim of an effect, it is their responsibility to provide the evidence. The clinician stating stretching should be applied must provide the evidence to support it, not the clinician abstaining from using the intervention. The burden of proof never lies on the individual questioning a claim. Anecdotal evidence and poor-quality trials are insufficient to justify treatment. This can be frustrating, especially when the anecdotal evidence is piling up and we lack the high-quality trials to back it up. It becomes more frustrating when looking at the body of rehabilitation literature and wondering if anything is evidence-based. The good news is we have strong evidence for many of our treatments, especially exercise. The bad news is our toolbox shrinks substantially when applying the filters of high-quality evidence.
Stretching for the fun of it
This may seem irrelevant to a clinician. You could make the argument that any intervention is “fun” (although, good luck with short wave diathermy). The fun does not mean efficacious. Yet, stretching does not have to be solely for improving mobility and attempting to facilitate healing and reduce future injury. Unlike some interventions, stretching can be enjoyable. There is a large psychological and placebo play as well. After sitting for a long period, going on a long run, or getting ready for bed, stretching can facilitate relaxation. The negative effects of stretching are short-lived and specific. The key is in the delivery.
If we are expressing to patients, stretching can be used for enjoyment, and not conveying physiologic benefits that are unfound in literature, there is no harm. Similar to treatments that are placebo, we must be open about the treatment we are providing and the effects it delivers. Stretching is no different.
Some readers may be thinking “absence of evidence does not equal evidence of absence.” True, but that does not provide a license to provide any treatment and simply say the right study hasn’t been conducted yet. Herein lies the danger of the confirmation bias and anecdotal evidence. We recall times when we provided a stretch and the patient reported feeling better. There are many issues with drawing a causal relationship with our anecdotal experience. The first is the lack of control. We cannot definitively conclude what caused the effect. It could have been a placebo, previous interventions, or natural course. The second issue is the effect size.
We can find some level of improvement with most interventions. But are they clinically significant? Are they greater than other interventions? We have a finite amount of time and our exercise prescription has limits. To maximize patient benefits, we must use the interventions that are must support in the literature.
The primary question remains, “what is the goal?” This requires a follow up of “does it matter?” For example, Marshall et al completed a studying evaluating the effectiveness of stretching to increase range of motion. They used a four-week stretching program consisting of four hamstrings and hip stretches performed five times per week. When stretched with the same torque and to the same level of discomfort, the participants increased their sit and reach test range about 16˚ or 20%. As we have seen with the aforementioned studies, outside of reaching a threshold for P.E. class fitness testing so your parents can proudly brag about their ‘presidential physical fitness’ child, the increase doesn’t provide much benefit. James Nuzzo sums up his view on using flexibility as a major component of physical fitness in his 2020 paper aptly titled “The Case for Retiring Flexibility as a Major Component of Physical Fitness”. He wrote:
“Flexibility has been researched for over 100 years. Its track record is unimpressive, particularly when viewed in light of other components of physical fitness. Flexibility lacks predictive and concurrent validity value with meaningful health and performance outcomes. Consequently, it should be retired as a major component of fitness”29
Some may view this as harsh, but he came to this conclusion after assessing over 300 studies on the topic. Even for the studies that show a benefit in performance or injury prevention, the effect sizes are small, and the study designs are weak. If we chose to provide an intervention, we must have rigorous evidence to support it. As stated, the absence of evidence is not evidence of absence, but that is not the issue with stretching. We have substantial evidence, and currently, it is weak regarding using stretching as a form of treatment for the purposes of performance, injury prevention, or healing. If the sole goal is short term-pain relief and the patient satisfaction increases, the evidence is in support of the decision.
We must be wary of anecdotal evidence. Stretching has been passed down unquestioned for generations in athletics and healthcare. It does not matter how large the sample size is, the lack of controls limits the utility of the information. The sunk-cost fallacy of past investments of time, money, and effort may tug at you. The confirmation bias of your past success following stretching or the anecdotal guarantee from a mentor or coach may weigh heavily on your mind as well. There are many cognitive biases at play when determining the best course of care. My ask is that you critically evaluate the evidence; look at both sides of any argument. It is not until we fully understand each side, that we can make an informed decision.
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