Outlining the Benefits and Risks of Passive Stretching 

I am going to start out with what has, at least historically, been an unpopular opinion:

Static passive stretching is probably one of the most effective ways to increase range of motion (ROM).

Before we get too far, there are a few definitions we need to iron out. First, range of motion, as defined by Physiopedia, is "the extent or limit to which a part of the body can be moved around a joint or a fixed point; the totality of movement a joint is capable of doing." Second, Mobility really refers to active range of motion (AROM). AROM is "the ROM that can be achieved when opposing muscles contract and relax, resulting in joint movement" (link). Third, Flexibility is simply the ability to adapt to different situations or demands (this can refer to physical adaptations, but it doesn't have to) and should not be confused with ROM or AROM.  Finally, stretching is lengthening tissues beyond their normal range but within their physiological range (paraphrased from the Yoga Medicine Yoga for Athletes Handbook). 

We use different types of stretching, then, to increase ROM. 

In a meta analysis* from 2018, (Thomas et al. 2018) researchers looked at 23 studies on stretching to see if they could identify any patterns in the kind of stretching, the frequency of stretching, the duration of stretching, and changes in ROM in participants over time. It turns out that participants who engaged in static stretching like those done in Yin Yoga had statistically significant gains in ROM compared to other stretching protocols** that included ballistic stretching and PNF (proprioceptive neuromuscular facilitation - now you can see why we abbreviate that 🤣). The researchers also found that the sweet spot for stretching frequency was five times per week for one minute for each area of the body. 

This study tells us that static stretching will help us get the greatest gains in ROM! This is good news! But has the internet made you afraid of passive stretching?  

Let's talk more about static stretching and the unpopular opinion that I cited above. First, static stretching has been demonized for permanently lengthening fascia and other tissues of the body to a point that joints are taken beyond where their end range of motion should be (here's an example of this criticism). However, I have two rebuttals for this. First, go back to our definition of stretching, above: Taking tissues past their normal range, (that would be the range they are in without any force put on them, whether the force is body weight, muscle contraction, or help from a trainer or prop), but within their physiological range. If the joints are going past their safe end range of motion and causing problems, then according to our definition, it's not stretching anymore. Based on what I've observed working with yoga students for the past eight years, most of us do not get to the point where we're even approaching the end range of motion in our joints. Of course there are exceptions. Of course their are people who go all out and push until they tear.

If you are worried, just ask yourself how much Yin yoga, specifically, you practice. Is it more than 5 hours per week? And were you diagnosed by a doctor for hypermobility? If the answer to both questions is "no," you are probably doing alright.

Second, passive stretching can create performance deficits in high performing athletes, and so plenty of people in the fitness world have recommended that people avoid doing it. This is because stiff (stiff in this context is the sciency word for tight) tissues spring back more quickly after load is released. So, tight legs will run faster than gummy bear legs because of physics. This doesn’t mean that athletes shouldn’t maintain a healthy ROM, but if they want to shave off time on their sprint, they aren’t going to want to make a chest-to-thigh forward fold a goal of their yoga practice. Stiffer, or tighter tissues such as the IT band, Achilles, and hamstrings are going to improve their speed. But here's my rebuttal: If you are a marathoner content with your four hour marathon, don't stop doing passive stretches. If you're a marathoner trying to win Boston, go ahead and check with your coach. (You never know - they might say that you should do 1 minute per day per area of the body where needed after your training session. Or they might say to focus on passive stretching in your off-season). 

In a yoga context, passive stretching happens most consistently in Yin Yoga classes, although you will find it sprinkled in to some of my Vinyasa classes, usually either towards the beginning or end of class (in the middle we focus more on AROM).

In Yin Yoga, poses are held for anywhere from 1 to 10 minutes, and we relax the muscles as much as possible in order to allow the stretching load to be placed on the fascia and other deep tissues of the body. Holding these stretches can trigger the parasympathetic nervous system response, which can help with muscle recovery. There is also evidence that these deep stretches hydrate the connective tissues of the body and may stimulate fibroblasts*** to lay down collagen in the areas that are experiencing stress. More collagen and hydration in and around the tissues means smoother gliding, less friction, more efficient movements, and potentially fewer injuries. 

If you are curious about Yin Yoga, try this class with me on YouTube 🤩

Notes

*A meta analysis is when researchers select a large number of research already published on a certain topic using predetermined selection and exclusion criteria. For example, maybe researchers will exclude stretching studies conducted on animals, and include stretching studies with human participants. Or they will exclude studies with small sample sizes. And so on. From there, they analyze the research protocols and outcomes together as a whole to get a sense of what the topic looks like on a broader scale. 

**A protocol in a scientific study is the thing that the researchers ask the participants to do. So the "stretching protocol" would be the stretching routine. 

***A fibroblast is a type of cell designed to secrete collagen. Collagen in turn help maintain the structural integrity of tissues.