Dynamic Stretching
For our finale on the topic of safe stretching, we’re going to discuss dynamic stretching. Dynamic stretching is categorized as movement that extends to our end range for a given muscle that doesn’t require a long hold at that end point. In other words, we move through it. We may hold it for a brief period of time, but it’s quite different than static or PNF stretching, in which we may hold certain positions for 5 to even 60 seconds per stretch.
What is Dynamic Stretching?
The Science
Dynamic stretching utilizes reciprocal inhibition to achieve results (Longo). If you recall from last week’s blog post, reciprocal inhibition is the concept that, as one set of muscles act on a joint (for example, the quadriceps contract to straighten the knee), the opposing muscles (in this case, the hamstrings) lengthen to allow this action to occur without injury.
There is something, however, that can counteract this lengthening we desire: the myotatic stretch reflex. This is the reflex that occurs when the doctor is testing your reflexes in his office during a routine physical. This reflex causes the muscle being stretched to tighten, or contract, to resist injury, with the goal of trying to keep the muscle the same length (not having it stretch too far).
When trying to stretch a muscle, like the hamstring, it also takes about 2 seconds to take effect. This is where timing for dynamic stretching comes into play. Dynamic stretching is only held for 0-2 seconds to bypass this reflex that some might say impede progress.
Obviously, it doesn’t impede all progress, as we already know that static stretching works. Again, it simply is using one reflex to our benefit while trying to avoid another that counteracts that lengthening. Neither way is wrong or right. Both aim to increase our flexibility by utilizing different mechanisms (ie, in different ways).
It’s also important to note here that dynamic stretching is not the same as ballistic stretching. Ballistic stretching involves quick contractions of the agonist muscle (for example, quadriceps) to lengthen the opposing, antagonistic muscle (in this example, hamstrings). There is no static hold at the end range for the muscle, which results in a bouncing movement that causes the joint to move into an extreme range of motion. This elicits the myotatic stretch reflex, which is the very reflex that dynamic stretching works to avoid (Longo).
How to perform dynamic stretching
Much like other types of stretching, there is more than one way to stretch your muscles. I’ll provide some examples here:
- Hamstring stretch: Lie on your back with a strap around your foot (like the one pictured here). Use your own strength to pull your leg straight up in the air while holding the strap (do not use the strap to hoist your leg up) until you feel a stretch in the back of your thigh (not pain). At that point, use the strap to provide assistance in stretching beyond your active range and into the passive range (again, not until the point of pain, just until the stretch is increased some, but tolerable). Hold this for 1.5-2 seconds. Then release your leg back to starting position.
- Adductors/Inner thigh stretch: Lie on your back with a strap around your foot and your leg turned out. Again, use your muscles (not the strap yet) to pull your leg out to the side and up towards your shoulder as far as you can without pain. Then, use the strap to assist the stretch a little further for 1.5-2 seconds. Then, release your leg back to its starting position.
- Quadricep stretch: Lie on your stomach with the strap around your foot or ankle. Bend your knee as far as you can, as if you were trying to touch your heel to your bottom. Then, use the strap to assist you in stretching further for 1.5-2 seconds. Then, release the lower leg.
- Plantarflexor/gastrocnemius stretch: Sit in long sitting with one leg extended straight out in front of you. Use a strap around the foot (if you can’t reach your foot with your hands), or if your hamstring flexibility allows, be ready to grab your foot with your hands. Actively flex your foot, pulling your toes back towards your head. Once you’ve actively reached your end range, assist your foot in stretching further by grabbing the ball of your foot or pulling on the strap for 1.5-2 seconds. Then, release.
By now, you should notice a few themes here:
- Actively move your limb into it’s end range with your own strength. This activates the agonist muscles to set up the stretch and keep the reflexes in check.
- Apply overpressure with a strap or your hands to increase your flexibility by shifting from your active range of motion to your passive range of motion.
- Hold for no more than 1.5-2 seconds.
- Return to your starting position.
Also, keep in mind that you don’t have to hold the stretch at all. Dancers accomplish this with leg swings. Baseball players and golfers do this by swinging their bat or golf club to warm-up.
These are examples of dynamic stretching.
Research and Evidence
There’s a fair amount of evidence in the scientific community since the 1990’s regarding dynamic stretching; however, several are small studies and some only involve men or women, which limits their generalizability. Keeping that in mind, Bandy et al found that both static and dynamic stretching improved flexibility, but that static stretching was the best method. This study, however, held their “dynamic” stretches for 5 seconds, which would trigger the myotatic stretch response that dynamic stretching was created to avoid.
Similarly, Meliggas et al studied 13-14 year old boys (I wanted to include this study here, as this blog is not only for adults, but also those who are up and coming and have an interest in optimizing their health), and found that both dynamic and static stretching improved range of motion.
O’Sullivan et al determined that static stretching was better at increasing range of motion than dynamic stretching. Longo concluded that AIS outperformed static stretching and PNF stretching in her study, although it was a small sample size (n=10).
A few other studies I found compared dynamic stretching and static stretching in terms of performance versus flexibility. Herda et al examined peak torque of the biceps femoris (the outermost hamstring) in 14 males after stretching statically (30 second holds) and dynamically (no holds, just moving through movement at end range for 30 seconds), and surmised that there was no decrease in peak torque (maximal muscle strength) after dynamic stretching while deficits surfaced after static stretching.
Amiri-Khorasani et al studied 18 professional male soccer players, and concluded that dynamic stretching allowed for better kicking leg forward phase and follow through phase range of motion over static stretching.
Finally, Maneol et al found that dynamic stretching was better than static stretching or no stretching regarding knee extension power in 12 women (although both static stretching and dynamic stretching increased range of motion).
What does all this mean?
Dynamic stretching can be a safe and effective way to stretch and increase flexibility. But if you’ve been paying attention to my previous blog posts about stretching, static stretching and PNF stretching both offer benefits, as well.
What this means is that there is no one right way to stretch. Everyone is different, and you have to find what works for you. That being said, you might want to consider when you’re performing your stretching, as some studies (but not all) have demonstrated that static stretching before jumping, balance, and agility activities could affect your outcomes in a negative way.
Perhaps dynamic stretching is best before class or before your workout with static stretching better once you’re finished exercising. Perhaps you don’t like static stretching, and PNF suits your needs.
You may have to try a few of these methods and see how you feel and how you perform. After all, you are your own n=1. Be your own experiment, and see what is optimal for you. And remember, there are always tools to help you along the way (such as a stretching strap, yoga block, YouTube videos, etc). Happy stretching!
Resources:
http://www.jospt.org/doi/pdf/10.2519/jospt.1998.27.4.295
http://www.ijastnet.com/journals/Vol_5_No_3_June_2015/13.pdf
http://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/1471-2474-10-37
http://repository.um.edu.my/6246/1/ACUTE%20EFFECT%20OF%20STATIC%20ANDDYNAMIC%20STRETCHING.pdf