The Myth of Safe Numbness

Overview

Many people think of tingling and numbness in rope bondage as having two distinct causes -- loss of circulation ("not dangerous") and nerve compression ("dangerous"). It's common to hear someone say "I'm feeling some tingling, but it's normal for me to lose circulation in this position, so I'm not worried about it".

While this is a very pervasive way of thinking, it is based on some faulty assumptions and outdated ideas.

The Old Model

The conventional logic goes something like this:

1. I can see from discoloration or other symptoms that there are changes in circulation. (usually accurate)
2. I know that it's common to have tingling/numbness caused by loss of circulation. (WRONG, for most people)
3. Since changes in circulation are present, the simplest explanation for my tingling/numbness is that it's from loss of circulation. (wrong, because 2 is wrong, and for other reasons)
4. I know that loss of circulation from bondage is not generally dangerous. (accurate)
5. Therefore, my tingling/numbness is not dangerous. (wrong, because 3 is wrong)

Even if you haven't encountered this type of reasoning before, it's good to learn to recognize it; for example, I recently (in 2024) was in a class at a reputable venue where the instructor was using similar logic to justify the safety of some really extreme techniques. When you spot that, it should be a prompt to think twice and do your own safety assessment.

A Better Model

Here's a more accurate way of thinking through the same situation:

1. I know that the most common cause of tingling/numbness is nerve compression.
2. I know that to substantially impair circulation requires an amount of pressure that will also affect nearby nerves.
3. Therefore, it's almost certain the tingling/numbness I'm feeling is contributed to by nerve compression.
4. I know that too much nerve compression will result in injury.
5. Therefore, the tingling/numbness I'm feeling could be a precursor to injury.

What about the different types of nerve sensations?

There's a widespread belief that tingling/numbness that occurs quickly and is highly localized is more dangerous than that which has a slow onset and is spread over a large area. There's no reason to think that isn't true, and we can make some reasonable guesses about what might be going on in this respect.

If a rope is pressing directly on a single exposed nerve, it can more easily apply higher levels of compression. We know that higher pressure is associated with more injury, and it's reasonable to assume it would be associated with faster onset. Conversely, if a rope is tourniqueting an entire limb, it will compress all the nerves, but likely apply less pressure to each. This latter situation is also the one that would cause circulation changes at the same time, which partly explains the false association of those feelings with "just" circulation loss.

So are more intense, immediate, or focal sensations more dangerous? Most likely yes. But that doesn't mean less severe symptoms are not potentially warning of injury; it's fundamentally the same bad thing, just less of it.

All the evidence for there being a difference at all is anecdotal, so we don't really know how predictive of injury different types of sensation change are. It's also important to keep in mind that these are not really two distinct phenomena, but two ends of a spectrum; real situations will often be a mix of both.

How much is too much?

So if it's all just different degrees of nerve compression, how much compression is too much?

Unfortunately the answer to this will be different for every body, on every day. More pressure and longer durations are always worse; but even keeping those fixed, what recovers immediately one day could be an injury the next. Maybe the most important thing to keep in mind is that nerve compression damage tends to build up over time. If you're constantly pushing the envelop, you're eventually going to pay a price.

It's very common to see the hardest-playing rope bottoms do all sorts of amazing stunts for a few years, and then retire with injuries that prevent them from doing that kind of rope anymore. I'm not saying there's anything wrong with that; elite athletes in many fields know they are going to use up their body in a decade or less.

The question you should be asking yourself is, do you want to do extreme rope for 5 years, or would you rather do more moderate rope for 50 years? If you're going to go hard and take damage, be honest with yourself that that's the choice you're making, and be sure it's for a good reason. Life is long and bodies are finite. You can have a profound connection with your partner without numb arms.

All the Gnarly Details

The chains of reasoning presented above make some assertions of fact without having explained where they come from. If you're willing to take my word for what's true and false there, you can skip this section. Otherwise, I'll do my best here to explain how I've come to those conclusions.

Medical studies on rope bondage are unfortunately thin on the ground, so there is a lot that can only be inferred from loosely relevant evidence. In the face of this ambiguity, I try to err on the side of caution; that is, if A or B are about equally likely, and B would result in increased risk, we should assume B.

I have had some kinky medical professionals review this material, and tried to incorporate their feedback; however I am not a doctor. I welcome any new evidence/interpretation.

Where the Idea of Loss of Circulation Comes From

We've all had the experience of a limb going to sleep in daily life. The usual folk understanding of this occurrence is that it's due to a loss of circulation from not moving, and that the limb waking up is about blood getting back into it. However, that is largely a misunderstanding. The medical term for these symptoms is transient paresthesia, and it has at least as much to do with direct pressure on nerves as with circulation (WedMD, Cleveland Clinic, video explanation (CW: internal anatomy)).

You've probably seen examples of light-skinned people in bondage with limbs turned dramatically purple -- that is a clear sign, and usually the first sign, of reduced circulation. Now think about times you stood up and discovered your foot asleep, or woke up with a dead arm; was the limb discolored? I bet it wasn't. That's because your overall circulation in the limb was fine, you were just resting with pressure on a nerve.

We naturally associate these everyday experiences with the pins and needles we sometimes feel in bondage, and are right to do so -- but the symptoms are the same because there is nerve compression in both cases. This same thing that is usually harmless in everyday life, with greater duration, pressure, or repetition, can cause an injury. In fact that happens outside the realm of bondage as well, such as in cases where a person is passed out drunk, or routinely wears an over-tight piece of clothing.

How Circulation Actually Comes Into Play

Blood Supply to the Nerves

Pressure on nerves has two effects that are almost always going to occur together. One is that the nerve itself is under mechanical strain. The other is that the blood supply to the nerve is impaired by compression of the small vessels that supply the nerve, and potentially of the nearby arteries that supply those vessels. This system of blood supply to the nerves is the Vasa Nervorum. When you compress the area near a nerve, you're likely both compressing the nerve itself, and reducing its supply of oxygen (causing ischemia). Because these occur together, it's hard to disentangle how much they each contribute to either the warning signs we may feel, or any injury that results. This ambiguity is sometimes called out in the medical literature on tourniquets, for example:

The 2 main mechanisms of pneumatic tourniquet-induced nerve injury are ischemia and direct mechanical effects (Hodgson 1994). Ochoa et al. (1972) found that compressive neurapraxia rather than ischemic neuropathy or muscle damage was the underlying cause of tourniquet paralysis.

A medical tourniquet is a fairly extreme situation, but other references indicate that these two effects also go together at lower levels of pressure. From Michael Stanton-Hicks, in Neuromodulation (Second Edition), 2018:

Blood flow inside the nerve is dependent on intrafascicular pressure (resting pressure ≈ 2 mmHg), and even more so within the endoneurium. A pressure below 20 mmHg has no effect on arteriolar or capillary blood flow and minimal effect on venular flow. However, with increasing pressure above 20 mmHg arteriolar flow will decrease. Venular flow ceases at 60 mmHg and there will be no arteriolar flow at 80 mmHg (Rydevick et al., 1981). In a similar manner, axonal transport is impacted by pressures above 20 mmHg (Lundborg and Dahlin, 1996).

While this whole situation is complicated, because these two effects occur together, it is not especially important for risk assessment purposes to disentangle them. Both come into play when there is pressure around a nerve; both cause symptoms; and both can contribute to injury. In other sections of this discussion, when I talk about "nerve compression", I am lumping these effects together; for bondage purposes, we don't know enough about their distinct roles to treat them separately, and anyway have some reason to suspect compression of the actual nerve is the main factor at play.

Blood Supply to the Limbs

We can imagine that if circulation is sufficiently cut off to an entire limb, eventually nerves will begin going to sleep from ischemia even absent any direct pressure on the nerve. This raises two questions -- 1) is it likely? and 2) is it dangerous?

The mechanism by which bondage most readily reduces circulation in a limb is essentially identical to a tourniquet, albeit a fairly ineffective one. As mentioned in the discussion of medical tourniquets above, in the average person, the forces needed to cut off all circulation with a tourniquet well exceed the threshold where nerves are being compressed. Because cutting off blood flow to a limb requires pressure all around the circumference, the nerves passing through the tourniquetted section of the limb will necessarily also be under pressure. So in this case, it's not likely that whole-limb ischemia will be the first factor to come into play.

Note that pretty dramatic changes in color can happen even when a limb is still getting a supply of oxygen; a moderate red/purple/dark discoloring means that more blood than usual is pooling in the limb due to veins being constricted more than arteries, so that it's easier for blood to get in than to get out. But that doesn't imply that no fresh oxygenated blood is getting in.

This situation shifts, however, if there are other factors impairing circulation. Medical conditions such as diabetes or Raynaud's can greatly reduce the baseline level of circulation in the extremities. In these cases, it is totally possible for generalized ischemia to cause nerve impairment, even without rope applied. So then we have to ask, under those conditions, is it dangerous?

One might think that this would finally be an example where pins and needles do not indicate danger, since it really is "just" loss of circulation. However, the same medical conditions that create a situation where this is likely to happen, also often cause nerve injury from chronic ischemia. While those nerve injuries usually occur gradually over long periods of time, an acute ischemic insult from rope bondage seems likely to contribute to any deterioration. Absent directly applicable studies, it is reasonable to assume these individuals are at increased risk of nerve injury at least proportional to their increased warning symptoms.

An Experiential Exercise with Loss of Circulation

Here's a little exercise that takes advantage of it being relatively easier to cut off circulation to small extremities, to experience loss of circulation distinctly from nerve compression.

Take a long piece of twine (18" or 0.5m), and wrap it lightly about the base of your little finger. After a couple minutes, you'll start to see some red/purple/dark discoloration. You may be able to feel your pulse in the finger, and/or notice it feeling puffy. These are the result of the blood pressure increasing in the finger, as the veins are obstructed more easily than the arteries by the string. You'll likely have no or only very minor changes in sensation. After you've observed these effects, take the twine off; the finger should return to normal almost immediately, with no dramatic sensation.

Now wrap the twine around again, more tightly (don't leave this on for more than 10 minutes). This time, especially if you are light-skinned, you may see a very different sort of discoloration; a blotchy combination of bloodless paleness with dark bluish-purple patches. Now you've cut off circulation entirely; little fresh blood is getting in, and the finger will feel cold, rapidly dropping towards room temperature. But it's still not numb! You'd have to leave this on for a while for ischemia to start affecting the nerves. Once you've observed the effects, take the string off; you may feel a kind of warm rush as blood floods back into the finger and it returns to body temperature.

Both of these sets of symptoms felt to me quite distinct from what happens when I sit on my foot and it goes to sleep. That is nerve compression; the above are loss of circulation.

Stages of Damage to Nerves

There are two distinct types of injury to nerves likely to occur in rope bondage, and understanding the difference can help shed light on differing experiences with recovery from injuries.

Neurapraxia is a condition where a nerve's ability to properly conduct electrical impulses is impaired by damage to the myelin nerve sheath. Because the nerve fiber (axon) itself is not destroyed, it may retain partial function, and will gradually regain normal function as the myelin is repaired; recovery within 6-8 weeks is typical, often with significant improvement in the first 2-3 weeks, or even sooner for less severe cases. Recovery is usually close enough to complete that the only noticeable lasting effect is a sensitivity to re-injury of the same nerve. This is the most common form of nerve injury in rope.

Axonotmesis is when the axon is damaged to the extent that it must regenerate from the point of injury outward. This regeneration is very slow (generally quoted as 1mm/day under good conditions), and so this type of injury takes many months to recover from, and you don't see the same early improvements as with neurapraxia (because until the new axon reaches its destination, it's not doing any good). Recovery is often good, but not always complete. In rope bondage, this type of injury is less common, but occurs under similar circumstances.

Wrist Drop and the Myth of the Correct Box Tie

The vast majority of debilitating rope bondage injuries are caused by a single tie, the box tie or takate-kote (TK), so it merits a bit of specific discussion. Some authorities whose entire style/career rely upon this tie have tried to promulgate the notion that injuries from TKs are entirely the result of incompetent practitioners, and that if you tie a TK "correctly" it is perfectly (or at least reasonably) safe. However, there are several major flaws with this idea.

Nobody Can Agree What Is Correct

If there were in fact a correct way to tie a TK, you would expect acknowledged experts on Japanese bondage to generally use similar approaches; but in fact there is tremendous diversity in all aspects of TK construction and wrap placement. Depending on whose style you observe, wraps may be high or low on the arm, with a large or small gap between wraps, totally parallel or with a sharp angle. Upper or lower kannuki may be present or absent in any combination. Suspensions may be loaded from the stem or the top wrap or both wraps.

Of course you may argue that each of these options has a time and place with a certain body and a certain suspension. However, there are no generally agreed-upon guidelines for selecting such combinations. Perhaps you are intended to come to intuit those choices after years of experience -- leading to a conundrum around what injuries you're going to cause on the way to gaining said experience.

The Data Indicates No Correct Choice

I performed a survey of TK-related injuries, analysis of which indicates that there's no single approach to placing the wraps of a TK that can be known in advance to be safe for any given individual.

Something That Must Always Be Perfect Is Not Safe

Even if you ignore all the evidence to the contrary and take as given that a sufficiently skilled practitioner can somehow choose the exact right TK for the situation at hand, then you have to ask -- is that person also infallible? If you assume that all the celebrated practitioners who nevertheless have caused injuries were insufficiently trained, and the lack of agreement between experts is due to the great subtlety of the art, then the "correct" TK must truly be a work of extreme skill and precision. Under such conditions, presumably even a small error could make the difference between a "safe" and unsafe TK. And who doesn't ever make a small error?

In any safety-critical field, you'll find numerous mechanisms in place to guard against the inevitable mistakes that human experts make. Pilots have checklists. Climbers inspect each others' knots. To call a system safe, you need to have a margin for error. In the theory of the "correct" TK, it's not clear where that margin would be.

Conclusions

The TK is not a safe tie. Is it less safe than other ties that put pressure on the upper arms? That's hard to say; it certainly causes the most injuries, but it is also by far the most popular.

Does that mean you shouldn't use this type of tie? That depends on your risk tolerances. However, in considering any potentially dangerous play informed consent relies on being informed. If you are misleading your partner (or yourself) into believing this is not a dangerous type of play, then your consent process is broken.