Anyways, beyond training stuff, I'm working on my research review for my thesis and had to write up an article on stretching for a friend to us. Below is my rough "blog" copy of the article. Usually how I go about writing, is just write it very casually just making sure to get all the points I need in there, then I go back fix a lot of stuff, make it "scientific" (which I hate to do), and clean it up. So, hope you enjoy.
Lastly, I think the most emails I get from everything I've ever written is on Strength Endurance work. Well, I'm probably going to video some strength endurance hill circuits in the next couple weeks (normally I've been the only one to do them in the past, but now athletes are older/more developed so they get to join in on the fun too!). So, you can probably look forward to that in 2-3weeks.
That's a couple things to look for in the coming month before I head back to school. In addition, I'll try and post my retrospective analysis on ryan and the other kids training the past track season. I did an analysis while in Europe, so when I have time I'll transcribe all my rough notes written all over last years training and put it into something useful for this blog.
Static Stretching's role in running:
Why flexibility isn’t all it is cut out to be.
Stretch, stretch, stretch. We are inundated with this idea that stretching is almost a cure all for all of our woes. Are you sore? Stretch. Want to prevent injuries? Stretch. Want to increase your speed? Stretch to increase flexibility. Want to run more efficiently? Stretch. Need to warm up before a race? Stretch. We’ve heard it all of our lives, but does it make sense? Is stretching and flexibility the cure all that it purports to be? Let’s take a look.
First off, there are several different types of stretching and flexibility. We will focus on the traditional static stretching and static flexibility. Now that that is out of the way, let’s dig a little deeper and see what happens when you stretch.
One of the major changes that occur when a muscle is stretched is a decrease in compliance and tension. A decrease in tension also means a decrease in stiffness. At this point, you may be thinking that that is a good thing. A looser muscle is better, right?
Not if you are running. Running relies heavily on what is called elastic storage and return of energy. It does so through many mechanisms. The key is that when your foot hits the ground, your bodies elastic parts (think mostly tendons) absorb some of the energy. Moments later that energy is then released and used to help propel you down the track or road. It’s almost like a shock absorber; the energy is initially stored and then released moments later.
It’s probably best to think of this as a spring. Take the Achilles tendon for instance. Upon hitting the ground, the spring compresses and is stored with energy. Once the spring is compressed, it then switches direction and starts to expand, releasing energy. That’s what happens in your bodies Achilles tendon, among other structures.
Similarly, elastic storage and return of energy plays a role in other joint structures. There is a stretch reflex phenomenon that occurs on certain parts of the body, one being the hip. When the hip is rapidly extended, the stretch reflex on the hip then causes the reverse to happen, shooting it back towards flexion. It’s like a rubber band effect. Stretch the rubber band rapidly, then let go, and it comes shooting back towards its original position.
What does this all have to do with stretching and flexibility? A stiffer spring stores and releases more energy. If you recall physics class, it’s simple physics. Hooke’s law clearly states that the force the spring will exert is dependent on the displacement of the spring, and the stiffness of the spring. The equation is F= -kx, where k is the stiffness constant and x is the displacement.
To simplify, a stiffer spring means more “free” energy, which means more efficiency. There is a reason that distance runners tend to get more inflexible the more they run. The body is amazing at adapting. If you start running 100 miles per week, it figures out how to make it easier on itself, so what does it do, try and become as efficient as possible by utilizing as much elastic return as possible.
Many of stretching’s effects are acute and transient, but its effect on the elastic storage mechanisms are both acute and long term. Stretching immediately before a run will decrease efficiency partly due to this, and long term increases in flexibility will also have the same result. Of course, it is important to remember that we are only looking at one variable. There are other benefits to stretching and there is a happy medium of how flexible you need to be. In general, the best advice I’ve heard on this subject for runners was from a Professor who had done numerous studies in this area, when he said long distance runners should probably never staticly stretch before runs, and only minimally after runs or workouts and even then not for an increase in flexibility.
But that isn’t the only change that occurs when you stretch. Another acute effect has been seen on motor unit recruitment. In several studies there has been a drop in motor unit activation by as much as 25%. Obviously with less muscle fibers recruited, less work can be done, which is not a good thing when you are trying for a maximal performance of any kind. Lastly, stretching also inhibits the stretch receptors (GTO’s and muscle spindles) which play a role in the stretch reflex mechanism, basically inhibiting and delaying that mechanism because the stretch receptor doesn’t kick in quiet as early to initiate that rubber band effect.
Let’s take a quick look at some of the claims on flexibility and see where we stand on each:
One of the major claims for stretching is that if you stretch after your workout, it will decrease muscle soreness from the workout in the following days. Sometimes you’ll even get the great line that it will help get rid of lactic acid. Well, it will, but not much faster than sitting there doing nothing, and not even as fast as if you got up and walked to your car. Clearing lactate isn’t a problem, if you just laid on the track following a workout; you’d be back to near normal levels in and hour or so. If you actually did a slow cool down, it’d be back to normal in as quick as 20 minutes.
As for muscle soreness, there have been many many studies measuring stretching’s effect on Delayed onset muscle soreness (DOMS), which is essentially the soreness that happens in the days following a workout. In almost every single study, there was no benefit of stretching. It did not help DOMS. There are several good reviews on all of the studies. If you really want to dig into it, check out, a good article is
Effects of stretching before and after exercising on muscle soreness and risk of injury in the BMJ by Herbert and Gabriel.
Makes you more economical?
Almost every single runner you talk to you will tell you that being more flexible will make you more efficient as a runner. This idea is VERY deeply ingrained into our sport. And on the surface it kind of makes sense, but if you really think about the mechanisms that impact running economy, then it makes absolutely no sense.
As I explained above, the body is incredibly reliant on the elastic properties for energy. Flexibility negatively impacts that. The theory is outlined above. But theory isn’t enough. We need some actual evidence. Is there any?
Of course there is! Have at it:
Sit-and-reach flexibility and running economy of men and women collegiate distance runners. Trehearn TL, Buresh RJ. J Strength Cond Res. 2009 Jan;23(1):158-62.
Conclusion: The significant relationship demonstrates that the less flexible distance runners tended to be more economical, possibly as a result of the energy-efficient function of the elastic components in the muscles and tendons during the stretch-shortening cycle.
Running economy is negatively related to sit-and-reach test performance in international-standard distance runners.
Jones AM. Int J Sports Med. 2002 Jan;23(1):40-3.
Conclusion: These results suggest that the least flexible runners are also the most economical. It is possible that stiffer musculotendinous structures reduce the aerobic demand of submaximal running by facilitating a greater elastic energy return during the shortening phase of the stretch-shortening cycle.
The association between flexibility and running economy in sub-elite male distance runners. Craib MW, Mitchell VA, Fields KB, Cooper TR, Hopewell R, Morgan DW. Med Sci Sports Exerc. 1996 Jun;28(6):737-43.
Conclusion: runners who were less flexible on these measures (dorsiflexion and hip rotation) were more economical.
I could go on, but that should be enough to get the point across. In general, the more flexible you are, the less economical.
Does stretching prevent injuries? Doubtful. How about does stretching CAUSE injuries? Well, I know I like going against the grain, but I would not push the envelope that far. However, stretching CAN cause injuries. Before you write this off as some insane theory, take a look at the reasoning.
Stretching inhibits many of the feedback mechanisms that help prevent injuries. The receptors in our muscles that tell the brain that a muscle is stretching to far and to stop it are delayed. The receptors around joints and tendons have the same response. But, don’t just take my word. In a Journal article entitled The Effects of Stretching on Strength Performance in Sports Medicine, Rubiini et al. state
“there seems to be a reduction in sensibility of the muscle, tendon, joint receptors and muscle nociceptors, which are fundamental mechanisms for protection of structures involved in motion. In addition to these alterations, there is a period where neuromotor responses are delayed immediately following stretching exercises. These acute neural alterations may be related to the observed decrease in strength and may predispose to or increase the risks of injury, although this requires further investigation.”
Flexibility and injury prevention is a tricky thing to study. Most of the studies are comparative between groups that do stretching and those that don’t, and counting how many injuries occur. This comparison isn’t the best, but even those studies show that there is no correlation between stretching and injury prevention. Just to present the evidence, in a review by Schrier et al in the Clinical Journal of Sports Medicine, they concluded that “The basic science literature supports the epidemiological evidence that stretching before exercise does not reduce the risk of injury.” And finally, in a review by Herbert and Gabriel, they concluded that “stretching before activity does not present a practical useful reduction in the risk of injury.”
Obviously there is more work to be done, but the point is that stretching and flexibility isn’t an all good, cure all, like many claim it to be. Like everything else, it is best in moderation. In fact, a recent theory by Knudson suggests a Bell Curve hypothesis that injuries occur with those who are at the extremes in Range of Motion ability.
Use during a warm-up?
Everyone knows that stretching before any activity is a must. It enhances performance, right? Well, no, actually, it hinders performance. More than any other topic on stretching, this one has the most evidence.
Remember back to what changes happen following a bout of acute stretching, among them decreased motor unit recruitment and decrease in stiffness of the system. These changes adversely effect performance. If we look at the studies on the effects of an acute bout of stretching we can see that basically everything is affected.
In the simplest of tests, one rep maximum declines by about 6-8% in a variety of exercises from bench press to knee extension. Looking at a little more complex activities, vertical jump performance is consistently impaired by about 4-5%. In addition, ground contact time was lengthened in one of the jumping tests, which if you know anything about biomechanics, is something we don’t want in running either. But it’s not just one off activities of pure strength or explosion that are affected. Muscular endurance also declined by about 20% when doing a bunch of knee extension exercises.
However, that’s not running. It’s great that static stretching takes away from all of these gym type exercises but what about a wholly dynamic and complex activity like running. It turns out, not surprisingly, to follow the same trend. In testing a group of track athletes from LSU (so you know they are solid athletes…), sprint times over 40m were impaired by about .1 of a second. Which doesn’t sound like much, but it is over only 40m and at that distance, that’s a good deal of time. Think of it this way, .1sec at 40m is equal to about .25 sec at 100m if you get the same decay, which the 20m split times in the study project you would still have some progressive decay. So, it would be like someone going from 9.95 to 10.20. That’s a huge difference.
There have been a couple other studies done on sprints and stretching and they show the same results. If stretching does hurt performance, the question becomes how much is needed to hurt performance?
We don’t have all the answers to that question but it seems like just a little goes a long way. With just one stretch, strength levels drop dramatically. Similarly, when comparing holding a stretch for 30 seconds and 15 seconds, the strength drop was the same, meaning that only 15 seconds seems to be needed to show negative effects.
What does all this mean? Warm-up dynamically. Run, do strides, have fun.
Is there anything potentially good about stretching?
I don’t want to hate on stretching too much. There has to be something new that is positive about it right? Well, there actually is some potential. If we look at the hormonal response to stretching (because after all stretching is active, not passive, like many assume), there is some promising finds. With animal studies, chronic stretching has shown to increase Insulin Like Growth Factor-1 (IGF-1) and Mechano Growth Factor (MGF) in mice and rabbits. If you pay attention to the performance enhancing drug news at all, you’ll know that IGF-1 is one of those en vogue drugs that athletes are taking. It serves as a mechanism to not only increase strength but also enhance recovery. So, if stretching increases the levels of IGF-1 and MGF then there is potential for stretching post workout to be very beneficial. Releasing these hormones after a workout or run would help initiate repair much faster, which would lead to increases in adaptation and performance. Some other evidence may help to support this theory, as stretching when combined with strength training has shown to potentially increase strength gains beyond that of just strength training by itself. The hormonal release theory might help explain this.
Does this mean I should stop static stretching?
Not necessarily. What it means is that it probably is not a good idea to do much stretching before workouts or races. This is one case where the theory and evidence agrees that it seems to take away from performance. Instead of static stretching, warming up dynamically with a good deal of running, strides, and some dynamic stretching seems to be the best approach.
However, static stretching is so ingrained in our sport that some runners would rather die then give up their static stretching routine before workouts or races. In those situations I’d suggest putting the stretching before any other part of the warm up. The running and then dynamic stretching could potentially cancel out the negative affects of stretching, but there haven’t been any studies on this, it’s just theory.
Post run or workout stretching could be beneficial, not for clearing lactate or muscle soreness, but in helping to get the body into an anabolic mode by the release of several growth factor hormones.
Unfortunately, we do not have an answer to how much you should static stretch as a runner. The evidence and theory tends to point towards the idea that less may be more, but how much is still at issue. In general, I’d advise to limit stretching to post run or workout. Even then, the goal shouldn’t be to try and increase static flexibility.