Advanced Nerve Safety [Level 2]
The Myth of "Safe" Numbness
We tend to think of tingling and numbness in rope bondage as having two distinct causes -- loss of circulation ("not dangerous") and nerve compression ("dangerous"). Many experienced bottoms believe they can tell the difference between these sensations, at least in certain circumstances. However, this is really just a convenient shorthand for thinking about a much more complicated set of phenomena, and in actual fact there is no distinct line between these two categories.
Stages of Damage to Nerves
Nerves are complex structures, and there is a gradient of possible levels of insult/injury:
Paresthesia occurs when a nerve has stopped functioning normally due to lack of oxygen; this may be because of direct pressure on the nerve, pressure on blood vessels near the nerve, or reduced circulation in an entire extremity. Any combination of these factors may also combine to reduce the supply of oxygen to the point where function is impaired. At this stage, no actual tissue damage has occurred, and normal function returns as soon as circulation is restored. This is what we typically mean by "loss of circulation", or a limb "falling asleep"; but note that the actual mechanism is most often compression of a nerve. If the oxygen starvation (ischemia) is sufficiently severe and prolonged, it can cause tissue damage and progress to more severe stages of nerve injury.
Neurapraxia is a condition where a nerve's ability to properly conduct electrical impulses is impaired by damage to the myelin nerve sheath. This may be caused by either mechanical stress or ischemia (in other words, all the same causes as paresthesia). Because the nerve fiber (axon) itself is not significantly damaged, it may retain partial function, and will gradually regain normal function as the myelin is repaired; complete recovery within 6-8 weeks is typical, often with significant improvement in the first 2-3 weeks, or even sooner for less severe cases. 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 at with Neurapraxia (because until the new axon reaches its destination, it's not doing any good). Recovery is generally good, but not always complete. This type of injury is mostly caused by strong mechanical insult to the nerve. In rope bondage, this type of injury appears to be less common than Neurapraxia, but with similar causes/circumstances.
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