It is a common site to see a high-level athlete stretching before a competition. This is despite a body of research that suggests long static stretches reduce muscular power, which can result in decreased performance. So, if static stretching reduces performance why do we continue to see so many top athletes continue to perform stretches when they are getting ready to compete?
As usual the answer is a little more complex than we would like with some studies suggesting stretching will decrease performance and others suggesting a positive effect or at least an absence of any negative effects. It seems the answer may lay with the issue of how long the stretch is held and how many times it is performed.
A large systemic review by Behm et al. (2015) of 125 studies involving static stretching found moderate reductions in performance when testing was done in the minutes following stretching. There was a great deal of variability in results ranging from improvements up to 5% all to the way reductions in performance of up to 20.5%. Clearly the specifics of the stretching protocol make a significant difference in the effects.
When studies measured aspects of power-speed there were reductions in performance reported 24% of the time, an improvement found 6% of the time and no significant changes 68% of the time. When the studies focused on strength-based measures there were no significant changes 42% of the time, reductions 57% of the time and only one instance of an improvement. While this moderate reduction in strength measures is larger than the overall small reduction for power-speed measures you do have to take into account that the studies measuring strength involved stretches held for significantly longer then for power-speed studies. This difference in time could explain the greater reductions in strength.
Some interesting trends start to show up when you break down the studies to those in which the stretching was done for less then 60 seconds as compared to those in which it was done for more. For power-speed tasks with less than 60 seconds of stretching there were no changes 76% of the time with reductions only 10% of the time and improvements 13% of the time. For power-speed measures when the stretching was held for more than 60 seconds there were no differences only 61% of the time and reductions in performance 39% of the time.
When the measurements were strength based and the stretches were held for less then 60 seconds there were no changes 73% of the time and reductions in strength in the other 27% of the measures. Strength measures with stretches held more then 60 seconds had no change only 44% of the time while over 55% of the measures showed reductions in performance. Again there were more negative changes in the strength measures then the speed measures with an even larger impact when stretches were held over 60 seconds.
Why does stretching reduce force production?
While there is no conclusive answer as to why we see a reduction in force production so often after stretching there are a few theories that seem to best explain why.
Reduced central (efferent) drive: Remember that much of the activity that happens at a muscle is the result of neuroreceptors and their associated afferent neurons sending messages back to the spinal cord. That feedback is then acted upon by the central nervous system (CNS) and a message is sent back to the muscle through an efferent motor neuron (nerves that send messages to the muscle from the CNS telling the muscle to contract). It is theorized that there are changes in the sensory feedback mechanisms that result in slower or reduced instructions from the CNS telling the muscles to contract.
Reductions in tendon stiffness: While we usually don’t associate the word stiffness with a positive effect in the body, when it comes to tendons sufficient stiffness is something we want. You have a lot of force that you are trying to transfer (and quickly) through those tissues and if they have reduced stiffness the response rate and force transmission can be reduced. If the tendon has reduced stiffness the muscle could be working at a shorter and weaker length. Yes, it seems counter-intuitive that that a stretched muscle could be working at a shorter length but that could be an affect of reduced tendon stiffness.
Muscle damage or fatigue: Small amounts of muscle damage may occur as the result of stretching and that damage can reduce the contractile force capacity of the muscle. The stretching may also reduce blood flow and the associated available oxygen to the muscle. This could lead to a build up of metabolic end products and reactive oxygen species.
Diminished electromechanical coupling: In order for a muscle to contract an action potential (electrical charge) must stimulate a release of calcium in the muscle that is necessary for the contraction process to take place. The stretching could impair the transmission of the action potential slowing down the entire contraction process.
Intermittent vs. Continuous Static Stretching
To differentiate the effect of intermittent vs continuous stretching, Bogdanis et al. (2019) conducted a study that compared 3 static stretches held for 30-seconds each with a 30 second rest interval between stretches to holding a single 90-second static stretch. This allowed for each testing situation to have the same total amount of time that the muscles were placed under stretch, just under different conditions. The subjects performed each testing protocol on different days and only stretched one leg. The opposite leg served as a control. Upon completing the stretching a single leg counter movement jump (CMJ) was performed immediately after and at 1, 2, 3, 4, 6, 8 and 10 minutes.
In the intermittent stretching group there was an increase in CMJ starting at the 2-minute mark and peaking at the 4th minute. Compared to the control leg there was a peak 8.1% increase in CMJ at minute 4. In the continuous stretching group there was an immediate decline in CMJ, and performance did not increase past baseline pre-stretching levels until 6 minutes in. Decreases in CMJ for the continuous stretched leg were 12-17.5% less than in the control leg. At all time conditions the intermittently stretched legs outperformed the continuously stretched ones.
Pinto et al. (2014) asked the question of what difference does a single bout of 30 seconds of stretching have as opposed to 60 seconds on vertical jump performance. They found that 60 second stretches resulted in decreases in jump height, average power and peak power as compared to the 30 second bouts. In this study only one round of stretches was performed but four different muscle groups were stretched.
What does all this mean for your workout and performance? If you or your client is an average person who is just trying to get fitter and healthier and little stronger the impact is not much. The decreases in performance from stretching before activity are not going to impact your training. Most people aren’t approaching their peak performances in everyday workouts and recreational sports. So, go ahead and stretch a little before your workout if it makes you feel better. It is probably best to keep stretches to 30 seconds and less. If you feel an area needs more then one short stretch it is ok to repeat that stretch. Save the longer, increased range of motion stretches for after you are done working out.
If you are a higher-level athlete for whom a few percentage points in performance will make a difference, then your pre-event stretching protocol does matter. For this group the current data strongly suggests making sure that pre-event stretches are kept to 30 seconds or less. Certainly, less than 60 seconds at the most.
A shortcoming of much of this research is that it is laboratory based and doesn’t necessarily accurately reflect the realities of real-life competition. The timing between when stretches are performed and the impact on performance in real life can be much longer then in the studies. Athletes may begin warming up as much as a half hour or hour before competition. There are still many unanswered questions as to what impact stretching will have on performance if it is done with a longer gap between stretching and performance. There are also issues of what difference does this have with highly trained athletes as opposed to recreational athletes and the average gym goer. The impacts could be quite different because of long term training affects. While these questions still exist and need to be studied, based on the current data the suggestions of limiting pre-training or pre-event stretches to less than 60 seconds and ideally less them 30 seconds are still recommended.
Behm, D.G., Blazevich, A.J., Kay, A.D. and McHugh, M. (2016) Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: A systematic review. Appl Physiol Nutr Metab 41: 1-11. Bogdanis, G., Donti, O., Tsolakis, C., Smilios, I. and Bishop, D. (2019) Intermittent but not continuous static stretching improves subsequent vertical jump performance in flexibility-trained athletes. Journal of Strength & Conditioning Research 33:1:203-210. Pinto, M., Wilhelm, E., Tricoli, V., Pinto, R. and Blazevich, A. (2014) Differential effects of 30-vs. 60-second static muscle stretching on vertical jump performance. Journal of Strength & Conditioning Research 28:12:3440-3446.