Do Muscles Lengthen When You Stretch? What's Actually Happening in Yoga
When I filmed my latest YouTube video, I'd had my hair cut about three or four weeks earlier. A few months from now, it will be noticeably longer. Hair actually grows. It adds brand new length.
Many yoga practitioners imagine muscles lengthen when you stretch the same way hair grows. You settle into a forward fold, feel that big sensation along the back of your legs, and picture your hamstrings growing a little longer every time you practice.
It's a lovely image. It isn't quite what's happening inside your body.
So, do muscles lengthen when you stretch? Yes, your muscle gets longer as the tiny strands inside it slide apart. Those strands do not change size though. Nothing in your muscle really grows during a single yoga practice.
In This Article:
What happens inside your muscles when you stretch
A simple hand demo you can try right now
Why your muscles don't grow like your hair
When muscles can change length over time
What Happens to Your Muscles When You Stretch?
Your muscles are made up of long, thin structures called muscle fibers. Inside each fiber are tiny strands that overlap with each other. (If you love the details, these strands are actin and myosin. For this conversation, all you need to picture is strands sliding past each other.)
Those strands slide back and forth against each other. That sliding is what makes your muscle longer or shorter.
Try this: interlace your fingers loosely in front of you. Imagine that your fingers are the strands.
Slide your fingers deeper together. They overlap more, and the distance from one hand to the other gets shorter. Your fingers didn't shrink. They slid past each other.
Now slide your fingers apart until only your fingertips overlap. The distance between your hands gets longer. Your fingers didn't grow. They slid away from each other.
That's what happens inside your muscle. When the strands overlap more, your muscle gets shorter. When they slide apart, your muscle gets longer. The strands themselves stay exactly the same size.
Want to see it in action? In this short video, I walk you through it with my hands.
Do Muscle Fibers Get Longer When You Stretch?
Yes. This is where it can get a little confusing, so stay with me here.
When the strands inside a muscle fiber slide apart, the fiber itself gets longer. When they slide closer together, the fiber gets shorter. The strands are what stay the same length. Every fiber in your muscle is changing shape this way, which is why your whole muscle can lengthen and shorten as you move.
You can see this in your biceps right now. Bend your elbow and your biceps shortens. That's a concentric contraction, a shortening contraction. Slowly straighten your elbow and your biceps lengthens while it's still working. That's an eccentric contraction, a lengthening contraction.
Same muscle, same strands, different positions. When you stretch your hamstrings in a forward fold, the same sliding apart is happening there too.
Your hamstrings attach from your sit bones to the top of your lower leg bones, just below your knee. In a forward fold, those bones move away from each other. The opposite happens when you come out of a forward fold.
For more on how muscles work in your postures, read Muscle Contractions in Yoga: The 3 Types You Need to Know.
Do Muscles Lengthen When You Stretch, or Do They Grow?
Your hair adds actual new length. Your muscle strands don't do that. Your muscles are built to be active, shortening and lengthening moment to moment as you move.
So when your hamstrings feel longer at the end of a forward fold, your muscle has changed shape. It hasn't grown. What has happened is that the strands inside your muscle fibers have slid further apart.
Does Yoga Lengthen Muscles Over Time?
Muscles can change length over time in certain situations.
The most obvious one is growing up. If I had the same size biceps now that I had at three years old, it would be really, really short for my arm!
Training can change muscles too. With consistent training, muscles can grow, and their length may change over time as well. When that happens, the strands still don't grow. Your body may add more of these tiny units end to end, like adding links to a chain. These changes take time, and they're small.
What doesn't happen is growth during a single asana practice. Any long-term change comes from showing up consistently over months and years. Pushing harder into one deep stretch is unlikely to speed it up.
Muscle length is also one piece of the flexibility picture. Ligaments and bone shape play a role too, which I explain in Why Your Heels Don't Touch in Downward Dog.
The Bottom Line
Do muscles lengthen when you stretch? Your muscle gets longer because the actin and myosin strands inside each fiber slide apart, and the strands themselves never change size. Muscles can change length over time through growth and training, and those changes are small and slow. In a single yoga practice, your muscles are changing shape, not growing.
Get Curious! Q&A
Do muscles lengthen when you stretch?
Yes. When you stretch, the tiny strands inside each muscle fiber slide apart, so the fiber and the whole muscle get longer. Nothing grows during the stretch. The strands stay the same size and change position.
What are actin and myosin?
Actin and myosin are the tiny protein strands inside your muscle fibers. They overlap and slide past each other. More overlap makes your muscle shorter, and less overlap makes it longer.
Does yoga lengthen muscles permanently?
Long-term changes in muscle length can happen with consistent training over time, and those changes are small. A single yoga practice does not add new length to your muscles.
What is the difference between a concentric and an eccentric contraction?
In a concentric contraction, your muscle shortens while it works, like your biceps when you bend your elbow. In an eccentric contraction, your muscle lengthens while it works, like your biceps when you slowly straighten your elbow.
Know your anatomy. Trust your cues.
When you understand what’s really happening beneath the surface, you stop second-guessing and start seeing your students clearly. The right words come easily, and your students feel the difference.
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About the Author
Dr. Trish Corley, PT, DPT, E-RYT 500, is a Doctor of Physical Therapy, former anatomy professor, and yoga teacher trainer. She has taught anatomy in yoga teacher trainings since 2011 and has led her own 200-hour trainings since 2016.