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How Does Stretching Actually Increase Flexibility?

There’s a fresh-off-the-press study about how stretching works that I thought you’d be interested in hearing about. (Yaayy!)

But first, a little background info:

Do you know what’s really changing in your body when you stretch and become more flexible over time?

It might seem like stretching makes our muscles “longer,” but it turns out it’s not that simple!

There are actually 3 main mechanisms proposed in the current research for how stretching improves flexibility:

Mechanical changes in the muscle – loosely meaning that the muscle becomes less stiff (less force is required to lengthen it to any given point).
Increased stretch tolerance – your nervous system allows you to go further by outputting sensations of discomfort later in the range.
Increased muscle fascicle length – the tiny bundles of fibers inside your muscles actually grow longer.

Well, a brand-new systematic review and meta-analysis just came out that explored these exact questions further: What actually leads to increased flexibility when we stretch? And do the mechanisms differ between:

Acute stretching (short-term changes, like what happens right after a stretching session), and
Chronic stretching (long-term changes from stretching regularly over time)?

Let’s geek out on what this study found! 🧠📚

“Mechanisms Underlying Range of Motion Improvements Following Acute and Chronic Static Stretching: A Systematic Review, Meta-analysis and Multivariate Meta-regression”

Study Highlights:

This 2025 paper analyzed 65 studies to explore the mechanisms behind ROM (range of motion) improvements from static stretching. Here’s what they found:

👉 Acute Stretching (after a single session):

Can lead to reduced muscle stiffness – especially when the stretch is moderate to high intensity. (This reduction in stiffness is just temporary, though – it resets to baseline shortly afterward.)
Doesn’t seem to change your stretch tolerance or fascicle length in the short term.

👉 Chronic Stretching (regular practice over time):

Reduces stiffness ✅
But also improves stretch tolerance (you feel more comfortable in deeper ranges!) ✅
Still no consistent change in fascicle length ❌
These effects were consistent regardless of factors like age, sex, or initial flexibility.

🧘‍♀️ Implications for our yoga practice:

Consistent stretching pays off: long-term flexibility gains are mostly about becoming more tolerant of the stretch sensation and gradually reducing muscle stiffness.
Your muscles aren’t necessarily “growing longer” – flexibility is largely a neuromechanical adaptation.
For short-term results (like after a single session), intensity matters – a moderate to strong stretch is more effective for decreasing stiffness.

What About Muscle Fascicle Length? How Can We Increase It – and Why Might That Matter?

Research suggests that muscle fascicle length can be increased through certain types of training – especially full range of motion strength training (which strengthens muscles in their longer lengths) and eccentric training (where muscles lengthen under load).

There’s also some evidence that very long-duration, high-intensity passive stretching might lead to increases in fascicle length. However, these types of extreme stretches aren’t practical in most real-life stretching contexts, and the research on their effectiveness for muscle fascicle length increases is still debated.

So why would increasing fascicle length be beneficial? Longer fascicles may help muscles generate more force at extended lengths and could potentially reduce injury risk– particularly in sports like soccer, where hamstring strains are common due to the high-speed demands of the game.

While there are always exceptions, in general, longer muscle fascicles are considered a positive adaptation for both performance and injury resilience.

I hope you enjoyed reading about this brand-new study! It’s the perfect example of how stretching isn’t about muscles being pulled longer – it’s about the nervous system, sensation, and mechanical adaptation over time.

Thanks for geeking out on stretching science with me, everybody! 🙌

Want to update your understanding of the science of stretching – with all the relevant info we need to know for our yoga and movement teaching and practice?

stretching science 101 course for yoga teachers

Take my Stretching Science 101 course!

This on-demand course is available now for all of my Continuing Education members to watch anytime, and it’s packed with info on the exact stretching science we’re talking about here – in a clear, accessible, and yoga-relevant way. 🙌

💡 3.5 CE hours with Yoga Alliance, too!

When you're ready to cut through the myths and get clear, evidence-based insight into how stretching really works, check out this new course!

Access it by signing up for my Continuing Education membership (which starts with a free week – whoo hoo! 👏)

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