Stretching: finally, some clarity

I’ve been sitting on this thought for months, so this post really is overdue. After all, the literature review was published way back in January and it’s already May. Remember that New York Times article that made the rounds (and may well continue to do so) on the Book of Faces and other social medias? Remember how that played a big role in the ‘stretching before exercise is bad’ movement? Well ahead of the literature review being published, Mike Boyle mentioned this idea in a talk I heard in December (and, to his credit, this was a talk that was recorded well before that…). Ever since then, I’ve been meaning to share this thought.

The backstory

To refresh your memory (or in case you are unfamiliar), over the past ten years or so, there have been multiple studies that have looked at the effects of static stretching on muscular performance. As recently as 2008, it made mainstream news (case in point: the aforementioned ‘article’).

  • Quick definition of terms, just in case: static stretching basically refers to lengthening a muscle until a stretch sensation is felt or until discomfort is felt and then holding it there for a period of time without changing position or moving, hence static. It’s worth noting that discomfort should not be confused with and does not mean pain.

The most popular finding of this body of research was that prolonged static stretching leads to a decrease in muscular performance. In some cases, they found a decrease in maximal strength; in others they found a decrease in the rate of force production (meaning decreased power).

  • Power, in this context, means the rate at which works gets done. Work is force times distance. So power represents the ability to do work quickly. Like when a base throws her acro partner into the air.

Now, I say most popular findings because some of those studies found no statistically significant link between static stretching and muscular performance. It’s just that those ones weren’t as newsworthy. This is where it gets tricky.

On the one hand, there was a growing body of research that was showing that static stretching had an impact on a muscle’s ability to contract forcefully and/or quickly.

On the other hand, the studies that didn’t show performance decrements weren’t necessarily any less valid. They just didn’t make it to the New York Times.

Coming back to the first hand, there are questions that people didn’t ask about the research findings. It appears static stretching can have an impact on the muscle’s subsequent performance…but how long does this impact last? How long is too long to hold a stretch?

And then there’s the fact that the overwhelming majority of studies measured performance (maximal performance) right after stretching. Perhaps the most important question we could ask is what if after stretching, we were to do a dynamic, movement-based warm-up before attempting to some sort of maximal performance?

Would that make the performance decreases go away?

In the small number of studies that looked at this very idea, it looks like they do.

Not so fast…

Drawing conclusions from research (or in this case, a review of the research) is rarely such a straightforward thing.

Holding a static stretch decreases muscle performance…a little

The available research tends to show greater performance reductions when stretches are held for longer than 60 seconds. Shorter duration stretching seems to impact performance less.

Holding a static stretch—even for as long as 60 seconds—has consistently shown only small decreases in performance…when ‘performance’ immediately follows stretching. Consider the implications for practice: it’s a trade-off. The benefits of stretching against the decrease in performance…but wait, there’s more:

But most studies measured only performance with concentric contractions or isometric contractions…there are very few studies that have looked at performance effects on eccentric strength or power.

  • Concentric muscle contractions involve the muscle developing tension as its getting shorter. For example, during a maximal vertical jump test, your quadriceps shorten as they contract and extend your knees.
  • Isometric muscle contractions involve no change in muscle length as the muscle develops tension. Imagine using a leg press machine with the weight set to 1000 lbs. You can press all you want—and your quads won’t change length at all. Isometric contraction.
  • An eccentric contraction involves a muscle developing tension as it lengthens. A silks performer doing a split between the fabric needs their hamstrings to be firing (developing tension) as they go into the split so that they don’t fall into an accidental over-split.

The few that have examined eccentric performance have shown a negative impact on performance. Such a small number of studies makes it difficult to draw conclusions, but we do know that most muscle strain injuries happen in the eccentric phase of movements/activities, so it’s clear that more research could be really helpful.

  • Even here, there’s room for research to influence practice…maybe if you’re going to be doing some active splits holds in training, holding a long split beforehand might not be the best idea.gymnastics-1156339

The relevance to circus should be clear: there are many movements that require muscles to be on while they’re lengthening.

Speaking of holding a split…

Behm et al.’s review found five studies that looked at post-stretching performance at different muscle lengths. Again, that’s simply too few studies to draw lasting conclusions from, but they found that when testing at longer muscle lengths, there was actually a strength increase. This points us to another area where some additional research would be handy: aerialists often need to be strong in positions where muscles are in a lengthened state. I wonder whether stretching the appropriate muscles before performing certain tricks could help reduce excess tone and leave the muscle better able to cope with higher threshold contractions in a lengthened position?

Dynamic Stretching: the contender (or current champion)

Because of all the interest in static stretching, dynamic stretching surged in popularity as ‘the way to go’ with respect to pre-exercise warm-ups. The long and the short of it (ha, now that is a pun!) is that dynamic stretching might contribute to some improvements in muscular performance, but it doesn’t seem to take away from it.

Dynamic stretching does do a very good job of elevating core and local muscular temperature, increasing nerve conduction velocity, improving muscle extensibility and accelerating energy production. All good things, I’m sure you agree.

Take home ideas

In practically all of the studies done in this area, performance was only measured up to about 10 minutes after stretching. For our purposes, we should take performance to mean everything you do after your warm-up: skill practice, act run-throughs, and the like. Any performance decreases resulting from static stretching were still present up to 10 minutes later.

Few studies measured performance after a stretch-then-dynamic-warm-up format. The ones that did all showed no significant decrease in performance.

Based on the current research on the subject and the needs of circus athletes, static stretching can be a useful element of a good warm-up. In order to avoid or minimize any negative performance effects from static stretching, hold your stretches for less than 60 seconds you do, do 5-10 minutes of dynamic, movement-based activity following static stretching.

Of course, the next question to consider is what are we stretching and why. For the general, recreational population, it’s probably worthwhile to do a bit of stretching after foam rolling and the follow it up with a dynamic warm-up.

Where things get interesting is when we consider the hypermobile folks out there. You guys shouldn’t be doing much stretching in your warm-ups at all. Your warm-up should be purely dynamic movement plus stability activations affair. (But we love stretching! I hear you cry. I know, I know. Trust me on this one).

I’m not done with stretching yet. More soon.