Two days ago, there was a great post about the neglected aspects of fitness, with stretching being one of them. Coincidentially, I was researching static stretching at that time because my physical therapist told me to stretch more to address my flexibility issues. And as a scientist, I wanted to know more about stretching, what it is good for, when to do it, etc., so I read through scientific literature. This is what I found, and I hope it'll contribute to the discussion around stretching & flexibility 
TLDR: A summary of this post can be found at the bottom in the "summary & conclusion" section.
Static stretching describes the lengthening of a muscle until you feel either a stretch sensation or discomfort (Cronin et al. 2008; Behm et al. 2004). Once you’re in this position, you keep the muscle stretched for a set amount of time (Ebben et al. 2004).
Interestingly, all scientific studies published to date unanimously agree that static stretching (or all forms of stretching, for that matter), significantly increase joint range of motion (ROM). And since flexibility is defined as “the ability to voluntarily move a joint through its full range of motion” (Page, 2012), it’s safe to say that stretching makes you more flexible.
For example, a meta-analysis (Medeiros et al. 2016) looked at 19 randomised controlled clinical trials which investigated the effects of static stretching on hamstring* ROM. All 19 studies in this meta-analysis compared a static stretching to a control group and didn’t include special populations (such as the elderly, children, or professional athletes). The exact stretching protocols differed between the studies, but they all took hip-flexion ROM measurements before and after hamstring stretching. Satisfyingly, all 19 studies in this meta-analysis showed that static hamstring stretching is superior to no stretching in increasing hip-flexion ROM.
Another literature review arrived at the same conclusion: After examining 5 randomised control trials with men and women in their 20s, they found that static stretching of the hamstring is effective for increasing hip-flexion ROM (Lempke et al. 2018).
Because the hamstring stretch is easy to perform and hip-flexion ROM can easily be measured, hamstring stretching is commonly used in such studies. However, the results are not limited to the hamstring and hip-flexion ROM, as a more comprehensive literature review of 125 randomised controlled trials (which also looked at muscles other than the hamstring) found ROM improvements after static stretching, but not after no-stretching (Behm et al. 2016).
\Side note: The “hamstring muscle”, as the muscles on the back of your thigh are usually referred to, actually consists of three muscles: the musculus biceps femoris, the musculus semitendinosus, and the musculus semimembranosus. They all have the same function, though, namely knee flexion and hip extension, so grouping them together makes sense (source: anatomy classes).*
It’s repeatedly been shown that static stretching increases flexibility, but how often and for how long should you actually stretch to get more flexible?
A recent literature review by Thomas et al. (2018) looked at 23 peer-review studies to address this question. What they found is that the best ROM improvements are achieved by stretching at least 5 minutes per week per muscle. Increasing total stretching time beyond 10 minutes (per week per muscle) didn’t seem to result in even greater ROM improvements. Hence, a duration of 5-10 minutes per week per muscle seems optimal.
They also looked at the stretching duration per session, and arrived at the conclusion that it doesn’t matter how long each stretching session is; less than 1 minute stretching per muscle per session was as effective as more than 2 minutes of stretching per muscle per session.
And then they also investigated if there is something like an optimal weekly stretching frequency. Indeed, their analysis suggested that 5-7 stretching sessions per week resulted in better ROM improvements than only 2-3 stretching sessions per week.
According to them, an ideal stretching schedule to increase flexibility could look like this:
The previous sections showed that static stretching will improve flexibility and how to achieve better flexibility. But is this actually a good thing?
Movement Patterns
In sports that require a high degree of flexibility to perform certain movements, such as ballet or martial arts, an increased ROM is vitally important (Gleim & McHugh 1997). So, in these sports it’s definitively an advantage if you stretch often to increase the ROM of certain joints.
Flexibility is also important in other forms of exercise, at least to a certain degree, to correctly execute a movement pattern. For example (and as many of you can attest to), back squat depth is highly associated with ankle dorsiflexion and hip flexion ROM (Kim et al. 2015; Gomes et al. 2020). However, whether or not an ass-to-grass squat is necessary is a different question, and will depend on the goals of the weight lifter.
Injury Prevention
When it comes to injury prevention, greater flexibility seems to lead to less injuries. For example, two meta-analyses of baseball players and other overhead throwers (e.g. tennis, handball) found that deficits in shoulder ROM were associated with higher shoulder and elbow injury rates (Bullock et al. 2018; Pozzi et al. 2020). The findings of these meta-reviews are probably generalisable to all kinds of body parts, but more studies are needed for confirmation.
Further, a flexibility imbalance might be associated with greater injury risk. This conclusion was drawn in two independent observational studies. The first study found that knee and lateral hip pain was more prevalent in senior ballerinas (n=30) with reduced hip adduction ROM (Reid et al. 1987). And the second study linked* a left-right imbalance in hip ROM to higher injury risk in female college athletes (n=138; Kapnik et al. 1991).
\purely correlational*
The believe that you should statically before a workout probably aims at injury prevention. And indeed, a meta-analysis showed some effectiveness of pre-workout static stretching for injury prevention in 8 studies, while another 4 studies showed no effect (Behm et al. 2016). The authors noted that the preventative effect of static stretching depends on the type of injury looked at, with static stretching being better at preventing muscle injury than overuse injury.
Another review came to similar conclusions as they reported lower incidence of muscle- and tendon-related injuries in pre-workout static stretching groups compared to control groups. But they also reported no apparent differences between stretching and control groups when looking at overall injury rates (Woods et al. 2007).
Probably, the reduced injury risk from pre-workout stretching has to do with it decreasing muscle stiffness, thereby “making it more compliant to eccentric contractions and […] reducing the amount of primary mechanical damage” (Howatson & van Someren 2008).
Static stretching after a workout can also help maintain full ROM after eccentric exercise (LaRoche & Conolly 2006; Howatson & van Someren 2008). Because the natural reflex of muscles after eccentric exercises is to shorten, with static stretching you act against these processes by elongating the muscles (Thomas et al. 2018). This will allow you to continue exercising with proper form, and can thereby prevent injury.
Importantly, none of the studies included in the reviews above found a negative effect of pre- or post-workout static stretching on injury risk. So, from an injury prevention point-of-view, static stretching before your workout probably doesn’t do much (apart from preventing certain types of injury), while stretching post-workout will help you maintain full ROM.
Static stretching is commonly used in the treatment of muscle and tendon injuries, such as muscle strains or tendinopathies.
Muscle strains are one of the most common injuries in sports medicine (Dueweke et al. 2017; Garrett 1996). They are defined as skeletal muscle injuries which result from excessive stretching during eccentric muscle contraction. The muscles most susceptible to muscle strains are those which cross multiple joints, such as the hamstrings, the adductor longus muscle, the rectus femoris muscle or the gastrocnemius (calf) muscle (Garrett 1996).
Factors protecting the muscle from strains are strength, muscular endurance and flexibility (Garrett 1996). Likewise, physical therapy to restore strength and flexibility after the acute phase of muscle strain is used to help with healing the injury (Noonan & Garrett 1996; Dueweke et al. 2017; Page 2012) and will lead to functional recovery (Kim et al. 2018).
Static stretching increases your flexibility, and it can also be used in the prevention and treatment of muscle injuries. So, does it prevent or treat delayed-onset muscle soreness (DOMS)?
Delayed-onset muscle soreness (DOMS) is probably familiar to anyone who has exercised at least once in their life, and it’s a rather unpleasant sensation to most. The severity of DOMS “can range from muscle tenderness to severe debilitating pain”, and peaks between 24-72 hours after the workout (Cheung et al. 2003).
Despite its high prevalence, the mechanism(s) of DOMS are not clearly established yet, and there are currently six different hypotheses: lactic acid build-up, muscle spasms, connective tissue damage, muscle damage, inflammation, and enzyme efflux (Cheung et al. 2003).
Since we don’t fully understand the mechanisms of DOMS, it’s also hard to come up with biologically sound prevention and treatment options. However, based on the six DOMS hypotheses, several plausible measures to both prevent and treat DOMS have been proposed so far.
For example, the literature review by Cheung et al. (2003) found the following measures to be effective for either preventing or treating DOMS:
This is in slight contrast to a 2018 randomised controlled trial with 30 men, which showed that low-intensity stretching after unaccustomed exercise can reduce perceived muscle soreness, but not markers of muscle damage or inflammation, when compared to high-intensity stretching or no stretching at all (Apostolopoulos et al. 2018). So, the alleviating effect they found is probably just placebo.
This being just a placebo effect goes along the findings of another literature review (Herbert et al. 2011) of 12 field- and lab-based studies with more than 2300 participants, which assessed the effect of pre-, post-, and the combination of pre- & post-exercise static stretching on perceived muscle soreness.
They found that on average, pre-exercise stretching reduced muscle soreness by 0.5 points on a 100-point scale, post-exercise stretching reduced muscle soreness by 1 point, and both pre- & post-exercise stretching reduced muscle soreness by 4 points. Given that these are ratings on a 100-point scale, there might be a positive effect of static stretching on DOMS, but it is practically negligible.
However, it’s important to note that none of the studies found a negative effect of static stretching on DOMS, so even if you do it, you probably won’t make things worse. And the placebo effect is actually a strong one, so if you think it helps you with managing DOMS, continue doing so.
Pre-workout (static) stretching can have beneficial effects on muscle injury rate and muscle soreness. But isn’t it true that pre-workout stretching will also lead to a decline in performance?
A meta-analysis of 104 randomised controlled trials with a total of 962 male and female participants found that pre-workout static stretching reduced maximal muscle strength by 5.4%, maximal muscle power by 1.9%, and explosive muscular performance by 2.0%, on average (Simic et al. 2013).
In the same meta-analysis, they also looked at the performance impairments in relation to the stretch duration (see table below). This data suggests that performance impairment increases with increasing stretch duration, and that maximal muscle strength faces the largest impairments after pre-workout static stretching (Simic et al. 2013).
90s stretching
overall
Maximal muscle strength
-3.2%
-5.6%
-6.1%
-5.4%
Maximal muslce power
+0.4%
-1.7%
-3.3%
-1.9%
Explosive muscular performance
-0.8%
-2.5%
-4.5%
-2.0%
Another meta-analysis of 125 studies by Behm et al. (2016) arrived at similar conclusions. They looked at the changes in performance measures (e.g., 1RM bench press, vertical jump height, sprint running time) with and without pre-workout static stretching.
Overall, Behm et al. found a 3.7% performance reduction after pre-workout static stretching, when tested within minutes (!) of stretching. They also found a similar dose-response relationship between stretch duration and performance, with stretch durations >60s resulting in greater performance decrease (-4.6%) compared to shorter stretch durations
TLDR: A summary of this post can be found at the bottom in the "summary & conclusion" section.
What Is Static Stretching?
Static stretching describes the lengthening of a muscle until you feel either a stretch sensation or discomfort (Cronin et al. 2008; Behm et al. 2004). Once you’re in this position, you keep the muscle stretched for a set amount of time (Ebben et al. 2004).
Does Static Stretching Increase Flexibility & ROM?
Interestingly, all scientific studies published to date unanimously agree that static stretching (or all forms of stretching, for that matter), significantly increase joint range of motion (ROM). And since flexibility is defined as “the ability to voluntarily move a joint through its full range of motion” (Page, 2012), it’s safe to say that stretching makes you more flexible.
For example, a meta-analysis (Medeiros et al. 2016) looked at 19 randomised controlled clinical trials which investigated the effects of static stretching on hamstring* ROM. All 19 studies in this meta-analysis compared a static stretching to a control group and didn’t include special populations (such as the elderly, children, or professional athletes). The exact stretching protocols differed between the studies, but they all took hip-flexion ROM measurements before and after hamstring stretching. Satisfyingly, all 19 studies in this meta-analysis showed that static hamstring stretching is superior to no stretching in increasing hip-flexion ROM.
Another literature review arrived at the same conclusion: After examining 5 randomised control trials with men and women in their 20s, they found that static stretching of the hamstring is effective for increasing hip-flexion ROM (Lempke et al. 2018).
Because the hamstring stretch is easy to perform and hip-flexion ROM can easily be measured, hamstring stretching is commonly used in such studies. However, the results are not limited to the hamstring and hip-flexion ROM, as a more comprehensive literature review of 125 randomised controlled trials (which also looked at muscles other than the hamstring) found ROM improvements after static stretching, but not after no-stretching (Behm et al. 2016).
\Side note: The “hamstring muscle”, as the muscles on the back of your thigh are usually referred to, actually consists of three muscles: the musculus biceps femoris, the musculus semitendinosus, and the musculus semimembranosus. They all have the same function, though, namely knee flexion and hip extension, so grouping them together makes sense (source: anatomy classes).*
How often and how long should you stretch?
It’s repeatedly been shown that static stretching increases flexibility, but how often and for how long should you actually stretch to get more flexible?
A recent literature review by Thomas et al. (2018) looked at 23 peer-review studies to address this question. What they found is that the best ROM improvements are achieved by stretching at least 5 minutes per week per muscle. Increasing total stretching time beyond 10 minutes (per week per muscle) didn’t seem to result in even greater ROM improvements. Hence, a duration of 5-10 minutes per week per muscle seems optimal.
They also looked at the stretching duration per session, and arrived at the conclusion that it doesn’t matter how long each stretching session is; less than 1 minute stretching per muscle per session was as effective as more than 2 minutes of stretching per muscle per session.
And then they also investigated if there is something like an optimal weekly stretching frequency. Indeed, their analysis suggested that 5-7 stretching sessions per week resulted in better ROM improvements than only 2-3 stretching sessions per week.
According to them, an ideal stretching schedule to increase flexibility could look like this:
- 5 stretching sessions per week, e.g., on weeks days with the weekend off
- 1min of stretching per muscle per session, resulting in a total of 5min per muscle per week
Is a large ROM and flexibility actually a good thing?
The previous sections showed that static stretching will improve flexibility and how to achieve better flexibility. But is this actually a good thing?
Movement Patterns
In sports that require a high degree of flexibility to perform certain movements, such as ballet or martial arts, an increased ROM is vitally important (Gleim & McHugh 1997). So, in these sports it’s definitively an advantage if you stretch often to increase the ROM of certain joints.
Flexibility is also important in other forms of exercise, at least to a certain degree, to correctly execute a movement pattern. For example (and as many of you can attest to), back squat depth is highly associated with ankle dorsiflexion and hip flexion ROM (Kim et al. 2015; Gomes et al. 2020). However, whether or not an ass-to-grass squat is necessary is a different question, and will depend on the goals of the weight lifter.
Injury Prevention
When it comes to injury prevention, greater flexibility seems to lead to less injuries. For example, two meta-analyses of baseball players and other overhead throwers (e.g. tennis, handball) found that deficits in shoulder ROM were associated with higher shoulder and elbow injury rates (Bullock et al. 2018; Pozzi et al. 2020). The findings of these meta-reviews are probably generalisable to all kinds of body parts, but more studies are needed for confirmation.
Further, a flexibility imbalance might be associated with greater injury risk. This conclusion was drawn in two independent observational studies. The first study found that knee and lateral hip pain was more prevalent in senior ballerinas (n=30) with reduced hip adduction ROM (Reid et al. 1987). And the second study linked* a left-right imbalance in hip ROM to higher injury risk in female college athletes (n=138; Kapnik et al. 1991).
\purely correlational*
Can you prevent injuries through stretching?
The believe that you should statically before a workout probably aims at injury prevention. And indeed, a meta-analysis showed some effectiveness of pre-workout static stretching for injury prevention in 8 studies, while another 4 studies showed no effect (Behm et al. 2016). The authors noted that the preventative effect of static stretching depends on the type of injury looked at, with static stretching being better at preventing muscle injury than overuse injury.
Another review came to similar conclusions as they reported lower incidence of muscle- and tendon-related injuries in pre-workout static stretching groups compared to control groups. But they also reported no apparent differences between stretching and control groups when looking at overall injury rates (Woods et al. 2007).
Probably, the reduced injury risk from pre-workout stretching has to do with it decreasing muscle stiffness, thereby “making it more compliant to eccentric contractions and […] reducing the amount of primary mechanical damage” (Howatson & van Someren 2008).
Static stretching after a workout can also help maintain full ROM after eccentric exercise (LaRoche & Conolly 2006; Howatson & van Someren 2008). Because the natural reflex of muscles after eccentric exercises is to shorten, with static stretching you act against these processes by elongating the muscles (Thomas et al. 2018). This will allow you to continue exercising with proper form, and can thereby prevent injury.
Importantly, none of the studies included in the reviews above found a negative effect of pre- or post-workout static stretching on injury risk. So, from an injury prevention point-of-view, static stretching before your workout probably doesn’t do much (apart from preventing certain types of injury), while stretching post-workout will help you maintain full ROM.
Does (static) stretching help with recovery from injury?
Static stretching is commonly used in the treatment of muscle and tendon injuries, such as muscle strains or tendinopathies.
Muscle strains are one of the most common injuries in sports medicine (Dueweke et al. 2017; Garrett 1996). They are defined as skeletal muscle injuries which result from excessive stretching during eccentric muscle contraction. The muscles most susceptible to muscle strains are those which cross multiple joints, such as the hamstrings, the adductor longus muscle, the rectus femoris muscle or the gastrocnemius (calf) muscle (Garrett 1996).
Factors protecting the muscle from strains are strength, muscular endurance and flexibility (Garrett 1996). Likewise, physical therapy to restore strength and flexibility after the acute phase of muscle strain is used to help with healing the injury (Noonan & Garrett 1996; Dueweke et al. 2017; Page 2012) and will lead to functional recovery (Kim et al. 2018).
Can static stretching alleviate DOMS as well?
Static stretching increases your flexibility, and it can also be used in the prevention and treatment of muscle injuries. So, does it prevent or treat delayed-onset muscle soreness (DOMS)?
Delayed-onset muscle soreness (DOMS) is probably familiar to anyone who has exercised at least once in their life, and it’s a rather unpleasant sensation to most. The severity of DOMS “can range from muscle tenderness to severe debilitating pain”, and peaks between 24-72 hours after the workout (Cheung et al. 2003).
Despite its high prevalence, the mechanism(s) of DOMS are not clearly established yet, and there are currently six different hypotheses: lactic acid build-up, muscle spasms, connective tissue damage, muscle damage, inflammation, and enzyme efflux (Cheung et al. 2003).
Since we don’t fully understand the mechanisms of DOMS, it’s also hard to come up with biologically sound prevention and treatment options. However, based on the six DOMS hypotheses, several plausible measures to both prevent and treat DOMS have been proposed so far.
For example, the literature review by Cheung et al. (2003) found the following measures to be effective for either preventing or treating DOMS:
- NSAIDs (non-steroidal anti-inflammatory drugs): e.g., ibuprofen, both prophylactic and therapeutic
- Massage: therapeutic (depending on the type and timing)
- Compression socks or sleeves: both prophylactic & therapeutic
- Light exercise: therapeutic
This is in slight contrast to a 2018 randomised controlled trial with 30 men, which showed that low-intensity stretching after unaccustomed exercise can reduce perceived muscle soreness, but not markers of muscle damage or inflammation, when compared to high-intensity stretching or no stretching at all (Apostolopoulos et al. 2018). So, the alleviating effect they found is probably just placebo.
This being just a placebo effect goes along the findings of another literature review (Herbert et al. 2011) of 12 field- and lab-based studies with more than 2300 participants, which assessed the effect of pre-, post-, and the combination of pre- & post-exercise static stretching on perceived muscle soreness.
They found that on average, pre-exercise stretching reduced muscle soreness by 0.5 points on a 100-point scale, post-exercise stretching reduced muscle soreness by 1 point, and both pre- & post-exercise stretching reduced muscle soreness by 4 points. Given that these are ratings on a 100-point scale, there might be a positive effect of static stretching on DOMS, but it is practically negligible.
However, it’s important to note that none of the studies found a negative effect of static stretching on DOMS, so even if you do it, you probably won’t make things worse. And the placebo effect is actually a strong one, so if you think it helps you with managing DOMS, continue doing so.
Does pre-workout stretching decrease your performance?
Pre-workout (static) stretching can have beneficial effects on muscle injury rate and muscle soreness. But isn’t it true that pre-workout stretching will also lead to a decline in performance?
A meta-analysis of 104 randomised controlled trials with a total of 962 male and female participants found that pre-workout static stretching reduced maximal muscle strength by 5.4%, maximal muscle power by 1.9%, and explosive muscular performance by 2.0%, on average (Simic et al. 2013).
In the same meta-analysis, they also looked at the performance impairments in relation to the stretch duration (see table below). This data suggests that performance impairment increases with increasing stretch duration, and that maximal muscle strength faces the largest impairments after pre-workout static stretching (Simic et al. 2013).
90s stretching
overall
Maximal muscle strength
-3.2%
-5.6%
-6.1%
-5.4%
Maximal muslce power
+0.4%
-1.7%
-3.3%
-1.9%
Explosive muscular performance
-0.8%
-2.5%
-4.5%
-2.0%
Another meta-analysis of 125 studies by Behm et al. (2016) arrived at similar conclusions. They looked at the changes in performance measures (e.g., 1RM bench press, vertical jump height, sprint running time) with and without pre-workout static stretching.
Overall, Behm et al. found a 3.7% performance reduction after pre-workout static stretching, when tested within minutes (!) of stretching. They also found a similar dose-response relationship between stretch duration and performance, with stretch durations >60s resulting in greater performance decrease (-4.6%) compared to shorter stretch durations
