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Note that this question is a mirror of this one on Due to the lack of answers, I thought here might be a good place to seek more. Feel free to answer in either.

There is a fairly wide spread belief within the Aikido community that all joint locks and some throws (or rather their break falls) are harmful to children. I am looking for actual evidence-based medicine research(1) on the medium to long term harm to the development of children's body. Adults can practice these locks for decades without any adverse effects as their bones, tendons, and so on are all finalised. On the other hand, kids bodies are still growing and might be much weaker to resist strain. That's the common view within the Aikido teaching world. I am looking for actual medical evidence of such.

For example, here are two common locks used in Aikido: kote gaeshi (supinating wristlock) and kote hineri (rotational wristlock). The former twists the write anti-clockwise, the latter clockwise if applied to the left hand.

kote gaeshikote hineri

Both can be very painful in the short term but once the lock is released the pain disappears. The goal of locks is to either cause the body to move in a predefined way (to set up for a throw) or to pin the target so they are disinclined to resist the pin. The locks are safe to practice on adults: they do not cause any short, medium, or long term damage if applied correctly. Of course, they could do grievous damage if applied in haste on unsuspecting targets. But damage is not the goal. Otherwise, we could not train! To be fair, pain is not the goal either.

(1) Answers based on either anecdotal evidence or hear say will attract down votes.

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I hope this does not break the asking for medical advise as I am not asking for advise, I am asking for medical research. However, this might break the "asking for reference material" which tends to be frowned upon. It works well as a skeptic question. Not sure if it fits here... – Sardathrion Aug 7 '14 at 8:57
You're asking for medical data, not advice. Big difference. The difference is between asking "what is <X>" and "should I <X>" – The Wudang Kid Aug 7 '14 at 12:16
@TheWudangKid: Indeed. I was pretty sure I would be on the right side of that but as this site is still in beta, everyone could have decided that any form of medical question is off topic. I am glad that this is not the case. – Sardathrion Aug 7 '14 at 12:25
Have you considered asking a medical professional? – Juann Strauss Aug 7 '14 at 14:04
@JuannStrauss: Yeah but WHY!!!. Curious mind want to know! ^_~ – Sardathrion Aug 8 '14 at 7:01
up vote 10 down vote accepted

I don't have medical studies, but I can at least point you in the right direction of what to look up, based on kinesiology and adult biology.

Tendon Plasticity

"Tendon Plasticity" (Viscoelastic tissue) - Tendons work somewhat like rubber bands - they have some stretch to them, but if you over-stretch them, just like a rubber band, it ends up loose and destabilized and doesn't ever come back to normal:

If the recovery time between successive exertions is not long enough for a given force and duration, the recovery will not be complete and the tendon will be stretched further with each successive exertion.

(If you want to go further in-depth, check out Chapter 2 of Tendon Injuries Basic Science & Clinical Medicine, which goes into the issues of mechanical loading and stress failure points for tendon tissue)

Joint locks often use the limits of a person's muscle/tendon length to get the "lock" - the wrist lock being a prime example - and you'll notice from doing wrist locks, some people have a lot more range of motion before they have to go with it - that's a matter of having more muscle/tendon length.

Regularly stretching (or having it stretched for you, via joint lock) can result in that permanent tendon deformation and joint destabilization.

Tendon Strengthening

Too much load, or too much stretching, is bad. Too little load, is also bad. The key to strengthening tendons is months of regular resistance/load, high rep or long holds, to increase tendon thickness:

Chart of Tendon Therapy vs Injury based on load/stress levels

What this means about adults vs. children

I'm not a pediatrician, but based on what I know above, the argument for kids to not do joint locks has some solid basis:

  1. Adults have had more tendon strength from natural thickening of tendons based on long term loading, whereas children it is easier to overpower their tissue strength.
  2. Tendon overstretching is effectively permanent damage (short of surgery and stapling), and opens you up for other injuries for the rest of your life

There's also a 3rd factor which is that joint locks rely either on end length of tendons, or compressing joint capsules, which, if done with too much force or repetition, permanently damages cartilage.

If you want more science or specific studies, I suggest looking for people who are versed in pediatric sports injuries, as you're likely to find more relevant information there.

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way too much text for me ... but +1 for nice color diagram ! – Thierry Savard Saucier Aug 8 '14 at 13:44
Well, OP asked for medical science, so I gave it to him. Even then this is a very watered down version. I can break it down in more layman's terms, but I've found most people tend to think you're "making things up" when you simplify past a point, even if it's true as far as function goes. – Bankuei Aug 8 '14 at 20:05
As the OP, I think there could me more to this but as it stands, it's a great answer. Many thanks! – Sardathrion Aug 9 '14 at 14:36
My training is in kinesiology & physical therapy, so I have a baseline level of the science behind it, but not specific to children. If you do find deeper science sources, do you think you could link it back in this question? I'd be happy to see more myself. – Bankuei Aug 9 '14 at 16:04
Aye, it is a very good answer. I just didnt bother to read it all, since I wasnt OP. – Thierry Savard Saucier Aug 11 '14 at 11:47

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