Flexibility and fascia: why mobility is more than stretching

You have been sitting at your desk for hours. At some point you notice that your shoulders are almost glued to your ears.

You tilt your head to the side. There is a pleasant pull, and for a moment things feel lighter. An hour later, everything is back to how it was.

Or that morning when you bend down for your socks and your back answers with a twinge. You stretch, you roll, you buy a new mat. And still the feeling remains of being stuck in your own body.

If you know this feeling, you are not alone. And maybe it is not because you don't stretch enough.

Most mobility programs show you exercises. I want to show you what happens inside you while you do them: in your fascia, in your nervous system and in the way your body evaluates pain.

What is fascia, and why can it signal pain?

Have you ever peeled an orange? Beneath the peel lies a thin white skin. It wraps around every single segment and holds everything together.

You can picture your fascia in a similar way. It wraps around muscles, bundles of muscle fibers, organs and blood vessels. And it connects all of this into a single web.

Fascia is more than packaging. It is a tissue that can feel.

For a long time, fascia was considered silent filler material. An international consensus statement in the British Journal of Sports Medicine now describes it differently. According to this statement, the fascial system forms a three-dimensional web of collagen-containing connective tissue. It runs through the whole body and allows the body's systems to work together in a coordinated way.

Now comes the part of this topic that fascinates me most. Fascia is not just structure. It is also a sensory tissue.

The Heidelberg neurophysiologist Siegfried Mense later summarized these findings, mostly from rat studies. In the back fascia, he found exclusively free nerve endings. Many of them respond even to light mechanical stimuli and could therefore also report position and movement. A large share of the fibers belongs to the sympathetic nervous system, the part of your nervous system that ramps up under stress. They could constrict blood vessels. And inflamed fascia contained more fibers carrying pain messengers than healthy fascia.

A Brazilian review compiled ten such studies in 2021. Its conclusion: there is both histological and functional evidence that the back fascia can mediate pain. In the studies, stimuli in the fascia led to longer-lasting and stronger pain than stimuli in the subcutaneous tissue or in the muscle.

Fascia also seems to play a part in muscle soreness. In a study from Aalborg University, 13 volunteers trained a lower leg muscle with unaccustomed braking movements. The next day, a saline solution injected into the fascia of this muscle hurt considerably more than all the other injections. This also held true compared with an injection into the muscle itself. You can find more on this in the article on muscle soreness.

And now you know why some tension feels more like burning than like a tired muscle.

Does stretching make muscles longer?

Maybe you have experienced it yourself. You stretch the backs of your legs for a few weeks. At some point your fingertips get closer to the floor.

It feels as if your muscles have become longer. Like a rubber band that you pull out a little further day by day.

This picture is so widespread that hardly anyone questions it. Research paints a different one.

A single small study can be a fluke. That is why it is worth looking at a larger analysis.

A review in the journal Physical Therapy calls this the sensory theory. During a stretch, the muscle does briefly become longer, because its tissue behaves in a viscous way. This lengthening, however, is temporary. After single stretching sessions and after programs of three to eight weeks, it is mainly the sensation that changes.

Imagine your nervous system as a bouncer. He decides how far you are allowed to go into a stretch. At first he only lets you in a little way, because he doesn't know whether it is safe. With every calm repetition, he learns. And he lets you go a little further.

The bouncer shows himself even more clearly when you look at areas that were not stretched at all.

Conversely, stretching also seems to change pain sensitivity. In a Canadian pilot study with 22 healthy people, the pressure pain threshold rose after a prolonged stretch of the lower back. This was true at the back and at distant sites of the body. The researchers emphasize, however, that pain sensitivity in the lab is not the same as pain in everyday life.

And now you know why the same stretch can feel quite different on a relaxed Sunday than after a day full of pressure.

Why stress can settle in your neck and back

A day full of emails, appointments and expectations. You haven't lifted anything heavy. And yet by evening your neck is as stiff as a board.

Maybe you have wondered how that can be. After all, you have only been sitting all day.

Stress can translate into muscle tension, measurably and sometimes unnoticed.

Why does your body do this? From the point of view of your nervous system, you can understand tension as a protective strategy. A tense muscle is ready to react. In a dangerous situation, that is smart. Under constant stress, it can turn into a habit.

Do you remember the sympathetic fibers in the back fascia? They are a possible wire between your stress system and your connective tissue. How strongly this wire influences tension and pain in humans, however, has not yet been clarified.

On top of that comes something you may know from your own experience: caution. Anyone who has ever thrown out their back badly often moves more carefully afterwards. That is understandable. A review from Maastricht University, however, describes how this can turn into a cycle. Fear of pain can lead to avoidance, heightened vigilance, tense muscles and guarded movements. In many people, these processes appear to contribute to pain becoming chronic.

And then there is the volume control. The pain researcher Clifford Woolf from Harvard Medical School has described how pain pathways in the spinal cord and brain can become more sensitive. Experts call this central sensitization. Then even small stimuli can trigger pain, like a smoke detector that goes off when you make toast. Woolf describes this state as persistent, but reversible.

Three more levels: immune system, metabolism, hormones

From the perspective of clinical psychoneuroimmunology, I look at four levels. You have just gotten to know the nervous system. The second level is the immune system.

The third level is metabolism. Sugar can attach itself to collagen, much like caramel sticks to a spoon. Experts call this glycation. An Australian study followed 344 adolescents with type 1 diabetes over several years. The researchers used the thickness of the plantar fascia, the fascia on the sole of the foot, on ultrasound as an indicator of sugar-bound collagen. In 38 percent it was abnormal, and these adolescents later developed complications in the eyes, kidneys and nerves more often.

This has not been studied directly for flexibility in everyday life. But it shows that your connective tissue can mirror your metabolism. You can read about how muscles play a part in blood sugar in the article on strength training with diabetes.

The fourth level is the hormonal system.

For me, this means: if you are chronically tense, you sometimes need more than a new exercise. Sleep, stress, inflammation, blood sugar and hormones may all have a seat at the table.

And now you know why a stressful day can make itself felt in your neck in the evening, even though you haven't lifted anything.

What can foam rolling, stretching and yoga do?

Maybe there is a foam roller under your bed. Bought with high hopes. Used with gritted teeth.

And maybe you have wondered whether the pain while rolling is a good sign. Or just pain.

Rolling and stretching are good door openers. In studies, however, the strongest protection against injuries comes from strength.

That leaves the question of how. Many rollers say something about “releasing adhesions”. A review by David Behm and Jan Wilke comes to a sober conclusion. There is not enough evidence that breaking up adhesions is the main mechanism. Other pathways are more plausible. Rolling could stimulate receptors in the skin and fascia and activate the body's own pain-inhibiting systems. The balance between the activating and the calming branches of your nervous system could also shift. Blood flow and the water content of the tissue could play a role as well.

In this picture, the roller is less a rolling pin that flattens dough. It is more like a voice that tells your nervous system: everything is fine here.

And classic stretching before exercise? A systematic review led by David Behm examined exactly that. Directly after static stretching, performance dropped by an average of 3.7 percent. With 60 seconds or more per muscle group it was 4.6 percent, with shorter holds only 1.1 percent. Dynamic stretching, meaning moving instead of holding, improved performance slightly. With all forms, the gain in range of motion usually lasted less than 30 minutes.

And what if it is not about sport, but about chronic pain? For low back pain, there is a particularly large amount of data on this.

Yoga combines stretching, strength and breathing. A Cochrane review led by L. Susan Wieland from the University of Maryland analyzed 21 studies with 2,223 participants. Compared with no exercise, it found small improvements in pain and function that were of little clinical importance. Compared with other back exercises, there was hardly any difference in function. According to low-certainty data, side effects occurred more often with yoga than without exercise. Mostly this meant more back pain, 43 instead of 9 cases per 1,000 people. The authors write that the choice may depend on availability, cost and personal preference.

One aspect rarely comes up in mobility videos: your heart. A review from the United States describes how regular stretching training can improve the way the autonomic nervous system regulates your heartbeat. This can be measured through heart rate variability. Possible mechanisms under discussion include more sensitive blood pressure regulation, relaxation and more nitric oxide in the blood vessels. Exactly how this works is not yet well understood.

Summarized from the meta-analyses and reviews in this article. You can find the figures and sources in the study boxes and in the list of sources.

And now you know why the gain from a stretch can fade after half an hour if you don't put it to use through movement.

That is what mobility is about for me. Not doing the splits. But a life in which movement feels natural again.

Mobility training that brings your nervous system along: three levers

Maybe you are now asking yourself: so what do I do differently tomorrow morning?

Here is my practical translation. Not a rigid rule, but directions you can adapt to your body.

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Where this topic connects

Flexibility depends on your nervous system, breathing, warmth and movement in everyday life. These articles explore the neighboring levels in more depth.

Frequently asked questions about mobility training and fascia