The goal of neurodynamic stretching is to stretch & stimulate nerve tissue specifically — not muscles.
Neurodynamic stretching is a technical type of stretching, usually provided by a professional, designed to treat neuropathy by stretching nerves. It is a bit obscure, and the science is thin, but it’s an interesting idea that’s been around for a long time. It may also partly explain why stretching feels good.
Some pain is caused by physical interference with nerves — neuropathies like carpal tunnel syndrome or sciatica.1 Neural mobilization or neurodynamics is a loose collection of experimental stretching and positioning treatments for neuropathy based on the idea that “unhappy” nerve tissue can be rescued by the stimulation of stretch.
But not just any movement! Only quite specific movements need apply. If you really know your stuff, you can stretch in a way that emphasizes effects on nerves rather than muscles and tendons. More specifically, it may be possible to slide them in their sheathes (neural gliding or, goofily, neural “flossing”), or just pulling on the whole thing (neural tensioning).
This is a good example of a specialized type of stretching that might have genuine benefits for some patients — perhaps more than stretching in general, which is hugely overrated as a therapeutic tool or pillar of fitness.2 If it works, it would be an impressive partial vindication of therapeutic stretching. Spoiler alert: no one actually knows if it works, because…
Neurodynamic stretching has barely been studied
Neural mobilization is a tough thing to test — technical, hard to standardize, rotten with confounding factors. The science is so threadbare that I’m going to skip citations other than a single review.3 Writing my own informal literature review would just be frustrating and disappointing for everyone, a doomed attempt to pull a useful signal out of a little bit of noise (an annoyingly common problem at the fringes of musculoskeletal medicine, which is surprisingly primitive in general4).
So neurodynamics is not a scientifically validated therapy. But it hasn’t actually been kicked to the curb yet either, it remains plausible and interesting, and no discussion of advanced stretching for pain would be complete without it.
Meet the wire-pipes
“Wiring” seems like the obvious metaphor for nerves, but “plumbing” is surprisingly apt as well. Nerves may not be as much like pipes as blood vessels, but they are actually more like pipes than wires when it comes to how they work. They are like fancy plumbing doing an impressive imitation of an electrical system.
All nerves are tubes filled with fluid. Although the fluid doesn’t flow, it is wet, which is necessary for all the messy chemistry that allows nerves to play with electricity (just like in batteries). Their clever simulation of a flowing “current” is achieved by ions zipping back and forth across the membrane (action potentials), not by flowing along the length of the nerve (think of a stadium “wave”).
No pipe or wire works like that, of course. These physiology metaphors always fall apart when you start looking too closely.
The chemistry of nerve impulses is sensitive to any interference with the integrity of that membrane. Wires can be kinked like a garden hose with no loss of functionality, but not nerves. Inflammation and other biochemical sources can also mess with nerve function (e.g. several poisons).
Many causes of neuropathy are simple, just straight up pinching. But there are more subtle paths to neuropathy — like not gliding smoothly in their sheaths. Most nerves have a wrapping, but it doesn’t function like the insulation on a wire. Nerves need their own specialized fluid environment for optimal function, so they are a fluid-fluid tube inside another fluid-filled tube. Nested pipes! Exactly like the way the brain and spinal cord are also packed in fluid, just smaller. The whole nervous system is packed in fluid like this, from nerves as thick as your thumb to nerves so tiny they make hairs look like tree trunks.
They are all packed in fluid, and they are all free to slide in those fluid-filled channels to some degree.
Unless they aren’t.
Larger peripheral nerves consist of bundles of nerve fibres, bundled into larger bundles along with blood vessels — nested “pipes.”
Tunnel syndromes and neural tension: the consequences of nerve snags (from the reasonably certain to the highly speculative)
Sometimes, due to pathological processes and physical predicaments, nerves get pressed against and stuck to the walls of their tubes, like microscopic velcro. This predicament is usually called “neural tension” or a “tunnel syndrome.” You don’t want this happening to your nerves any more than your cat wants tape on its paws. It affects their function.5
There are several infamous and obvious “tunnel syndromes,” most notably carpal tunnel syndrome.6
Subtler tunnel syndromes
For every pathologically blatant tunnel syndrome, there are likely many subtler ones, which are probably to blame for a lot of milder neuropathy. This is not especially controversial. This scenario is usually called “neural tension” rather than a “tunnel syndrome.”
But what if we ventured even further out onto this limb? What if the most subtle neural stuckness can cause symptoms that would never actually be diagnosed as neuropathy? Just vague aches and twinges and discomfort? Some experts have proposed that these little micro nerve entrapments are actually the specific cause of the “trigger point” phenomenon — humanity’s plague of unexplained sore spots.7
An interesting hypothesis, but that’s all it is so far. It’s completely unclear whether these subtler scenarios happen at all, and to what degree.
Free the nerves! The point of neural mobilization
You may have guessed it from the setup: the goal of neural gliding is to free the nerves, by stretching in such a way that they actually pull free of their adhesions and entrapments. Sounds traumatic, but it could be so microscopic that we don’t feel a thing as it happens, or only the normal discomfort of a strong stretch.
Anything that feels like a stretch is undoubtedly causing many, many nerves to slide in their sheaths to some degree, and maybe this is a reason why stretch feels good/healthy: because it breaks up lots of little neural adhesions. Probably not much more than miscellaneous physical activity, and maybe not all, but still, it might be why people like stretching. Just keeping those wire-pipes slip-sliding around nicely!
Neural gliding as a formal therapeutic method is more focused: specific stretches based on detailed anatomical knowledge required to apply maximal tension to specific nerves. There are professionals who have devoted a great deal of energy to learning how to tug on many different nerves. (Heck of a thing, pursuing so much specialized knowledge about a largely unvalidated approach to solving a problem.)
And what about neural “tensioning”?
Neural gliding has the relatively obvious goal of breaking adhesions between nerves and their sheathes. But the point of neural tensioning is just to pull on nerves, without optimizing for “glide” of the nerve within a sheath. That is, some stretches pull on both sheath and nerve more equally.
I am not aware of any specific rationale for just generally stretching nerves, other than the simplistic idea that it’s basically a way of stimulating/exercising them.
Nerve tension and stretch tolerance
Hitting the natural and pathological limits of how far nerves can be pulled is one of the things that determines how intense a stretch feels. We may think we’ve stretched as far as we can not because we’ve hit the mechanical limit of the extensibility of our tissues, but because we’ve moved a nerve as far as it can be moved in its sheath. Nerve stretch may be what causes discomfort when you’re deep in a hard stretch, and it might be why some stretches are more unpleasant to hold than others.
This is particularly important because our “tolerance” for stretch is probably the main thing that changes when we increase our flexibility — not the actual physical properties of our tissues. I explore this concept in great detail in my stretching article.
About Paul Ingraham
I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of ScienceBasedMedicine.org for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter.
What’s new in this article?
Although first published as an independent article on Jun 8, 2021, the content was originally created a bit earlier as a chapter for my stretching article on April 25. I decided it warranted a page of its own.
Jun 10, 2021 — Miscellaneous editing and revision after publication as an independent article. Added artwork and pull quotes.
June — Publication.
- Well-known neuropathies include sciatica, carpal tunnel syndrome, and shingles. Banging your “funny bone” (the ulnar nerve) is technically a brief, trivial neuropathy. In musculoskeletal medicine (the focus of PainScience.com), we are mostly concerned with relatively simple neuropathies caused by impingement and trauma, and not so much by disease… but not necessarily. Pain is complex, and sometimes it is caused by neuropathy with a complex pathological backstory.
- Stretching is not a pillar of fitness: it doesn’t warm you up, prevent or treat soreness or injury, or enhance peformance, but it can cause injuries and (slightly) impair performance. It’s possible to increase flexibility, but the value of flexibility is surprisingy low, even for most athletes. Many key muscles are mechanically impossible to stretch in the first place. Stretch might help some kinds of pain, like muscle pain, but that’s quite speculative. There is no “advanced” stretching method that overcomes any of these limitations. See Quite a Stretch: Stretching science has shown that this extremely popular form of exercise has almost no measurable benefits.
- Basson A, Olivier B, Ellis R, et al. The Effectiveness of Neural Mobilization for Neuro-Musculoskeletal Conditions: A Systematic Review and Meta-Analysis. J Orthop Sports Phys Ther. 2017 Jul:1–76. PubMed #28704626 ❐
The level of evidence for neural mobilization is “largely unknown” according to this review of forty studies (only seventeen with a low risk of bias, and with lots of variety in methods throughout). The results were mixed, and NM notably failed for relatively straightforward peripheral neuropathies like carpal tunnel syndrome — if NM is good for anything, it should be good for that, at least.
On the bright side, according to the paper, the data “reveals benefits of NM for back and neck pain,” but these are complex conditions and notoriously multifactorial, so I remain pessimistic in the absence of more and better data. As the authors understate: “Due to the limited evidence and varying methodological quality, conclusions may change over time.” I’d say it’s so likely that “conclusions may change” that the word “conclusion” isn’t really useful here.
- We can put a man on the moon, but we can’t treat chronic pain. The science and treatment of pain and injury was neglected for decades while medicine had bigger fish to fry, and it remains a backwater to this day. The seemingly simpler “mechanical” problems of injury and rehab have proven to be surprisingly weird and messy. Oversimplification and quackery still dominate the field. For more information, see A Historical Perspective On Aches ‘n’ Pains: We are living in a golden age of pain science and musculoskeletal medicine … sorta.
- The membrane of the nerve itself is no longer floating freely, so ions can no longer rush in and out of that section of membrane quite so well. The result: pain, numbness, tingling.
- The tunnel term mainly refers to glaring cases of nerves that have gotten pinched in some of the larger, more obvious nerve sheathes, like the carpal tunnel. The tunnel can get narrowed by various mechanisms, like swelling, and adhesions may also form (basically getting pinched and then also stuck).
- Quintner JL, Bove GM, Cohen ML. A critical evaluation of the trigger point phenomenon. Rheumatology (Oxford). 2015 Mar;54(3):392–9. PubMed #25477053 ❐ Quintner et al. have hypothesized that “irritated peripheral nerve trunks” are “a rich source” of pain, and may be the true cause of trigger points, rather than the more conventional idea that they are “micro cramps.”