by [anonymous]2 min read10th Oct 201023 comments


Personal Blog

I once met a guy who practiced aikido and explained a little about it to me.  Aikido is a martial art, but it focuses in particular on what I'd think of as "body hacking."  There are ways to make your opponent trip and fall, or use his strength against himself; there are ways to pick up and throw a much heavier and stronger opponent.  Of course, because of this, there's often a lot of mystery and hokum surrounding aikido, but this guy said he belonged to a particular branch where, instead of venerating tradition, they try to come up with new "body hacks" and have worldwide meetings to test and compare them.  

The relevance to LessWrong is tangiential, except that this seems like a model of rationalism applied to things that seem like magic: it's a good example of how one should behave when faced with the inexplicable.

This dude demonstrated (and taught me to perform) a "trick" that I would not have believed possible.

First, hold out your arm straight and stiff and ask someone to push it down.  You can offer resistance, but if your opponent is strong enough, or if enough people are pushing down on your arm, you'll eventually fail.

Now, instead of holding your arm out stiff, make it as loose and floppy as you can.  Then hold it out, but think of "reaching" through the air, but without moving.  (As a visual aid, Aikido Guy held out a Coke bottle and asked me to hold my arm out while thinking of reaching for the bottle.)  Now get someone to push your arm down.  You are much, much stronger.  And you don't feel like you're expending any effort.  Nobody could push my arm down.  Aikido Guy, who is very small, told me that he'd once gotten three varsity football players hanging off his arm without budging it.

Aikido Guy was curious about this mystery, and luckily he was on a university campus, so he asked to be wired up to an MRI while he tried holding his arm out both ways. Apparently there was a real difference in the way the neurons fired. When he was trying to hold his arm out "stiffly," his brain stimulated all the muscle fibers in his arm, but intermittently (compared to the timescale of neuronal activity.)  When he was "reaching," his brain stimulated a smaller fraction of the arm muscles, but continuously.  Apparently the former kind of muscle stimulation is more tiring and weaker than the latter.

So, although we don't really understand what's going on, we do know that there's a physical explanation for it. (Do any of you have a better explanation?)


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23 comments, sorted by Click to highlight new comments since: Today at 4:58 PM

I've recently been learning swing dance aerials. I will let you into a secret: they're easy. Provided the height/weight ratios between partners are within certain tolerances, and provided everyone's knees and elbows and shoulders are in the right place, that girl has to go over that guy's shoulder. A pair of complete novices could probably learn any given aerial move in under an hour.

Many flashy jaw-dropping feats you see people do, in many performance arts, usually stem from there being an easy way to accomplish something that looks incredibly difficult. Fire eating is literally sticking a flame in your mouth and extinguishing it, but has a method so basic an eleven year old chemistry student should be able to tell you how it works. It's probably easier than the swing aerials.

Learning to lead and follow properly, though, (the bit no-one notices), that takes weeks and weeks.

This is why I always feel weird watching the more "artistic" gymnastics-like events in the Olympics. I don't know what I'm supposed to be impressed by.

I didn't believe the arm trick would work, so I went downstairs and got one of my roommates to push my arm while I tried the stiff and reaching versions. He was able to push my arm down both times without apparently trying harder in the latter case. As far as I can tell, I followed the instructions. What are the likely failure modes?

[-][anonymous]12y 4

I would guess it's being sufficiently "loose" before you start to reach, because he had to physically wobble my arm around before I was "loose" enough.

Of course it's also possible that this doesn't work all the time and it's some kind of group hypnosis -- which would still be interesting in its own right.

[-][anonymous]12y 2

Years of learning Aikido really should change the way the muscles are activated. So it would be surprising if no change showed in the MRI. You probably were mentally prepared when you tried, so that experiment was biased. Hypnosis is know to affect muscles so no surprise there either.

So my prediction is that these kinds of hacks only work with considerable preparation. Still it's good to know that they work in principle.

I was once told by a chiropractor that your ability to hold your arms out straight in front of you relies on your "foundation" or your posture or something. He demonstrated by easily pushing my arms down when I held them out in front of me, cracking my back, and then being unable to push my arms down (I realize this could be biased but it felt like he was using the same amount of force and I carried out the experiment with someone else who had gone.)

I realize that believing things that chiropractors say might be a candidate for the irrationality thread here but the explanation wasn't mystical, just if your back is having trouble that might make your arm strength weaker in a non-obvious way.

I actually have been having back problems lately, although it didn't feel like the arm pushing experiment involved any of the muscles that have been causing me trouble.

I really don't know enough to say more but if you have the ability to get into contact with a masseuse or chiropractor to discuss it with then this seems like a back-problem-improving experiment waiting to happen.

When you refer to a chiropractor, are you talking about this chiropractic?

Yes, although I would note that the practitioners I was in contact with were definitely "mixers" as the page calls them, and didn't really talk about anything mystical, and as I mention in the thread they seemed to be concerned with providing evidence that treatment was helpful (though I never pressed the issue much).

I suspect general muscular issues, not just my back acting up, since I've got some co-occurring pains in other areas to the point where I walked around with a cane yesterday. The doctor didn't recommend a chiropractor or anything more interesting than Motrin.

That sounds terribly unpleasant! I'm sorry! I hope you feel better.

You could test whether the problem lies in the granularity with which you or he can assess the level of pressure applied by trying a variant: Place your hand on his shoulder, elbow down, and attempt to hold your arm stiff while he pulls down on your elbow with both his hands. Then, in the same position, attempt to point or reach behind him while he does the same thing.

Since he'll have to exert more effort in both cases, the difference in effort should be more apparent.

I'm surprised at the MRI story. But I'm not surprised that a straight arm is easily pushed down compared to a slightly bent arm. I don't think any recourse to muscle fiber recruitment is needed to explain it.

Since I'm not sure I understand exactly what happened based on your description, I'll try some variations with a friend. Are you certain that the configuration of the bones was the same in both cases? This is really the most likely explanation.

Also, I can't believe in anyone holding up 600lbs with anything but the shortest lever arm (roughtly: horizontal distance from the center of support (somewhere between your two feet) to their attachment point. Something has gotten lost in the retellings.

[-][anonymous]12y 1

I hadn't thought of this, but my experience with weights has definitely indicated that slight (and not obviously visible) differences in joint position make a big difference in strength.

I've always been fascinated by the fact that, individual bone/muscle length differences aside, there really are far superior techniques for kicking a ball, jumping, lifting a weight overhead, etc. to the ones that I'd improvise on my own.

Learning physical skills is very satisfying. I have no idea if it helps the brain handle more abstract learning, if it interferes, or if it has no effect outside of the obvious physical exercise.

I believe that if you stiffen your arm, you're tightening opposing muscles, so you're working against yourself.

You have a stretch reflex which automatically compensates for pressure, and I assume it comes into play for a relaxed arm.

Cheng Hsin is a martial art which includes working towards deeper relaxation than I would have thought useful. On the other hand, Peter Ralston, who invented it, was the first non-Asian to win the world full-contact martial arts tournament in China, so he might know what he's talking about.

He's taken introspection into how movement and intention work deeper than anyone else I can think of.

Peter Ralston, who invented it, was the first non-Asian to win the world full-contact martial arts tournament in China

This sort of claim is often the sign of a martial arts crackpot.

I believe that if you stiffen your arm, you're tightening opposing muscles, so you're working against yourself.

This is the explanation I've heard. When you stiffen your arm, you basically fire up all your arm muscles, and they oppose themselves in such a way that the net effect is zero. But this makes it very easy for anyone to bend your arm because the you've essentially canceled out your resistance.

It's interesting that being able to feel your own strength means you aren't able to use it.

This sounds like a useful metaphor to add to the standard Deep Wisdom.

FWIW, I just tried this casually (holding out one arm and pushing it down with the other) and it worked; from the inside it feels like NancyLebovitz's explanation: "stiff" makes the muscles oppose each other (without much regard for position), whereas positioning my hand somewhere engages the normal feedback loops which keep my arm where I want it to be.

I've seen several carny tricks involving the ability of a person to resist downward force through their outstretched (ground-parallel arm) hand. I never cared enough to get to the bottom of it. Ultimately it's a weight lifting exercise (with a variable weight). Various factors may prevent you from actually using the right muscles (maximally). Shoulder joint rotation would matter. Consciously or habitually activating supporting shoulder girdle muscles would be very helpful, as would shifting more of your weight to the opposite foot. I agree that it would be cool to know all the possible reasons for someone to perform poorly (given their actual level of strength), especially if each had a simple practical demonstration.