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There are arm-toughening drills in many martial arts. Usually, this consists of banging various parts of your arm against a partner's arm or a tree or other immovable object. I've been concerned about the wisdom of this particular practice and whether or not it should have a place in kung fu practice.

Many martial arts also have sensitivity drills such as chi-sao or hubud-lubud. Some martial arts, for example Northern Mantis, Wing Chun, and Hung Gar, have both arm-toughening and sensitivity drills. These ideas seem at odds with each other. The stated purpose of banging arms in arts like Karate and Kung-Fu, is to either:

  • Decrease the intensity of the shock when someone blocks your strike or you block someone else's strike
  • Deaden the nerves in the arm for delivering blows

I'm not much of a one for anatomy, but for simplicity's sake, I'm going to refer to three striking surfaces of the arm:

  • The radial bone and accompanying nerve
  • The ulna bone and nerve
  • The muscle between the radial and ulna bone

Some arts, like Isshin-ryu, will only block with the last striking surface (muscle blocking). I think that's a pretty good idea. This is because that surface has very little nerve to damage. The nerves needed for sensitivity drills like chi-sao are the radial, ulna, and the under-side of the wrist. Only blocking with the muscle part of the arm seems ideal. Still, it seems like the other surfaces would need to be toughened in case they are banged by a block or strike.

I have heard it said, in Karate circles especially, that the purpose of toughening hands and arms is to break through armor. This is obviously horse manure. If it ever was possible to break through armor, that is no longer necessary in this day and age. I'd rather be able to practice martial arts and still type than to have deformed claws for hands. More moderate Karate practicioners say the idea is to toughen your bones so that you can break other people's bones. Okay, I dunno if that's the best way to go about it, but I can get behind that. But sensitivity is more valuable to me than toughness in the arts that I practice. Still, I can see value in toughening the arms so that they are more resistant to hard impacts. Is there a balance here? How does one toughen the arms without killing the nerves?

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3 Answers 3

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The primary reason why people bang up their limbs (arms, legs, elbows, knees, and head) is to be able to lessen the pain of the impact. Secondarily, by lessening the pain, the body is able to make mechanical adaptations to improve the power of the strike.

First with regards to the pain lessening...

While I do believe this does deaden the nervous system's response, I do not think it's generally permanent. It's short-term, probably on the order of a day before the effect starts to wear off. And it lasts maybe a week or two before it goes away completely.

Also, I don't think it's actually damaging the nerves themselves. Probably it's simply causing the brain to reduce its perception of the pain, basically dialing down the "volume" of the pain that the brain hears.

When a nerve in your limbs feels pain, it sends a pain signal to the brain. In the brain, neurotransmitters are responsible for communicating the pain signal to the brain's neurons. You only "experience" the pain at this point.

What happens next is the brain responds by secreting neurotransmitter blockers that prevent the pain chemicals from causing further pain. (The same thing happens when you take an aspirin, by the way.) Repeated doses of pain, will raise the base level of these neurotransmitter blockers so that it takes stronger and stronger amounts of pain for it to be felt by the brain.

And so what you're actually doing when you hit your limbs hard against stuff is increasing the base level of pain blocking chemicals in your brain. That lets you experience less pain. And it wears off over time, if you stop doing the exercises that cause pain.

Unlike taking an aspirin and having it lessen all of the pain you feel in your entire body, this effect is localized to the neurons that are associated with the particular limbs that were hit. And there might be some pain blocking going on right at the source (the limb's nerves) instead of just inside of the brain itself... But at this point, I'm in over my head, since I'm not a neuroscientist. Hehe.

Now, when nerves are seriously damaged (for real), they won't respond to sensation at all. Not just pain, but all sensation including touch and temperature. Your arm, for example, will be numb for weeks after that, unable to even feel normal touches. Or you might feel something, but it won't feel normal. Usually the body can heal minor nerve damage and even reroute signals to the brain to bypass damaged or dead nerves. In worse cases, this damage is more or less permanent, though there might be some sensation on occasion. The body is basically unable to repair it. In the worst cases, the nerve is completely severed, and you feel absolutely nothing ever again.

The moment you damage your nerve, it will sometimes feel like a sharp, shooting electric pain going up the limb, followed by pins and needles and then numbness. Also, when this happens, it's not just pain that will be numbed. It will be all sensation, including touch and temperature.

This is generally NOT what people feel when they perform the "iron body" stuff that martial arts practice. They are still able to feel touch and temperature just fine. It's just that the pain they feel will be lessened. So this is why I say it's probably mostly happening in the brain by increasing levels of neurotransmitter blockers, rather than actually damaging the nerves themselves.

The second part of what's going on is mechanical adaptation. That's where you learn to adjust your body's mechanics to allow you to use the limb to hit harder. If you anticipate that it will be too painful to hit in such a way, you will not really "lean into" your technique. You'll be too timid. And so your mechanics will not be as strong. But when you are sure it's not going to hurt, you start to make those mechanical adaptations to increase the effect and power of your strike.

Now, what I left out was bone strengthening. The theory goes like this: Micro-fractures in bone cause rapid mineralization of the fracture site, filling it up with calcium to reform the bone. So by repeatedly causing these micro-fractures, over time it can lead to a much stronger bone.

But it turns out that might not actually be true. According to some medical doctors, the fractures do increase strength temporarily, but eventually the bone becomes as weak as any other part of the bone, meaning that it's just as likely to break there as any other part of the same bone over the long term: http://www.nytimes.com/2010/10/19/health/19really.html

Of course, that article refers to medical bone breaks and fractures. But what about martial arts micro-fracturing? All bets are off. I don't think it has been sufficiently studied to say either way.

My feeling is that there probably will be some increase in bone strength, but it will only last until you stop the iron body training. At which point, it will probably return to normal strength. Most likely, then, what people perceive as their bones getting stronger is actually just a lessening of pain and an increase in power due to mechanical adaptations as a result (mentioned above).

One of the things you can definitely do to increase bone density and bone volume is to start doing weight lifting exercises. Increasing the load (weight) your bones have to endure will cause your bones to grow. This is described in Wolfe's Law. But once again, this is temporary. Your bone's strength will decrease again after you stop loading it.

Anyway, how important is this "iron body" practice in martial arts? Well, that depends on the style. Styles that do a lot of iron body training probably need it more than styles that practice it less or not at all. Without it, hitting your bones against something will cause a lot of pain, and that will cause you to be timid about using your bones in the way in which your style requires. Some say that's probably a good thing, some obviously would disagree.

Muay Thai, for example, uses the shin in its version of the round kick. They practice by hitting stiff punching bags at first. And then later on they'll work on hitting their shins against harder objects. The object is to lessen pain and make the shin bone stronger. This in turn gives them confidence enough to swing their legs really powerfully without worrying about breaking their shin bones. And in general, it works in their favor. But that's because they typically land their round kicks on their opponent's softer areas, like the thigh muscles and the abdomen. But they often do break their shins when they try the same kind of kick on an opponent who turns his knee into the shin. That happens because the lower part of the tibia (shin bone) is inherently weaker than the top part of it (just below the knee). Probably no amount of toughening exercises can make up for this difference.

So in the end, maybe it's just the pain lessening and mechanical adaptation that's important. The bone strengthening is probably a red herring. Or at the very least, it's overemphasized. In my opinion.

Final word about safety: Obviously, iron body training can cause permanent nerve damage. So work up to it gradually. If you feel shooting pain, pins and needles, or numbness, stop immediately and don't return to it until you know you can handle it and have corrected whatever you were doing wrong. Because, like I said, normally this shouldn't happen. Start slowly and gradually increase force.

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Not all nerves do the same thing!

So, here's a thing: not all nerves do the same thing, and you can deaden the pain nerves without losing movement sensitivity.

Movement sensitivity is primarily from proprioception, much of which the nerves that you'd be using measure the length of your muscle spindles and how fast they're being contracted/lengthened. Likewise pressure sensitivity isn't the same as pain sensitivity, which is why novocaine at the dentist's office stops pain, but you can generally feel them pressing and rooting around in your mouth.

It's really about bone

That said, deadening the nerves may reduce the amount of pain you feel in blocks/strikes, but it's not really the reason for arm conditioning. The reason is for bone strengthening - you have to apply stress along the directions you want bones to grow strong in - in most cases, your radial/ulnar bones are designed to take pressure length-wise, not cross-wise. So, the constant banging is to create microfractures to harden the bones to reduce the odds of a break.

But is it practical?

Well, it's pretty iffy to me. It makes sense of you're doing Muay Thai or a sport where everyone else is ALSO doing bone conditioning and you expect to take a lot of hits to your shins, forearms, using people's full body weight.

Everything else, odds are someone who can hit you with enough force for it to matter is probably using a club or some kind of weapon, in which case, you don't want to take that hit, you want to avoid it or jam it early. You want to do a little bit more for feeling how to take strong hits and keep your structure, or to push through pain, but constant banging doesn't make a lot of sense to me for modern combative needs.

What's it mean for you?

  1. Arm toughening will not lose your movement sensitivity - so if you want to do that, it's fine.

  2. Arm toughening can reduce your pain sensitivity (and some other, non-combative sensitivities too).

  3. Arm toughening can improve your bone strength against cross-ways force, though the amount of work for what you get from it makes it questionable as a useful practice.

If you do a lot of hard blocks against things like roundhouses, it might make a lot of sense to go with. Otherwise... it really comes down to your preference and making sure you can keep your structure against force and also your ability to deal with pain.

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That was a good point about there being different types of nerves. I didn't make that distinction in my answer. +1 –  Steve Weigand May 29 at 18:18
    
What is a pain nerve and how is that different from a movement nerve? Where should I bang my arm to hit one and not the other? Diagrams preferably. –  The Wudang Kid May 29 at 20:12
    
en.wikipedia.org/wiki/Golgi_tendon_organ The Golgi tendon organs measure muscle tension and speed of length change in muscle. These are your primary forms of proprioception sensation used for "feeling" where your body is positioned. This is different than the pain/motor nerves that actually go through your muscles. Since they don't go through the muscles themselves, you don't hit them when you bang your arms. –  Bankuei May 30 at 16:52

Funnily enough, I was just reading about this on BadMartialArts.com due to a different page's crosslink. They give a fairly comprehensive explanation of what's involved on a physiological level in conditioning. One of the major takeaways is that part of the conditioning is building up the muscles and learning to tense them properly against a blow to absorb the impact. And part of it is just a matter of getting used to the pain rather than actually damaging nerve endings.

Ultimately, as stated at the end of Steve's answer, if you're trying to avoid long-term damage, it's like anything else in exercise. Start gradually and back off if you start getting negative effects.

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