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In several martial arts (e.g. karate, muay thai), there are methods for toughening body parts (such as the fists or shins) by hitting them against hard objects. I am an amateur martial arts fan and wonder if these techniques are valid.

Does hitting hard objects actually strengthen and toughen a fighter's bones? What is the physiological explanation for this?

Are these a waste of time, or do the drills only make one used to the pain? It appears to me that the damage of such training goes well beyond the benefits.

I would gladly hear any scientific reasoning for or against such training.

  • No. To extend on that, not unless you actually injure your bones. Repetitive bone injury definitely would harden them, but I strongly advise against this. If you can't figure out why, it's not your bones that are soft... – LemmyX Jan 13 at 4:00
  • @LemmyX so are all seiken hardening and shin hardening drills in karate and other disciplines waste of time? – codezombie Jan 13 at 21:08
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    @LemmyX Please write an answer instead of answering in a comment. – mattm Jan 14 at 17:49
  • @mattm I left it as a comment because my answer wouldn't be long, and probably wouldn't be a very helpful one. – LemmyX Jan 16 at 15:35
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Yes, but... (and it's a big "but")

Two things stimulate bone density:

Damage

Generally our biological systems are set up so that if something is damaged, cells lay down more, tougher material since clearly what we had before wasn't quite tough enough. In other tissues, this forms as scar tissue which can reduce your mobility, however bone just gives you denser bone.

The ideal way to do this is minor damage, which, you can get from impacts. Of course, you need to have a certain bone density to begin with, otherwise you're just putting yourself into deep trouble (see what happens when people with osteoporosis take a fall...).

The other issue is that if you actually break a bone, there's no guarantee it will heal correctly or the joints will be aligned exactly right either, even with medical care. Some repairs are too hard even for surgery to get back into place and they just settle for giving you a fake hip or throw a pin in to hold it together.

Weight (resistance to force)

Strain against force (in our daily lives, that's gravity + our activities) increases bone density. This is why the #1 recommended activity to avoid bone loss or increase bone density is resistance training.

This is safer and generally better researched as the method to use. The only draw back is that some forms of increased bone density are harder to implement. For example, people toughen the center of long bones because it's tricky to set up weight across it easily, while clanging forearms against a training partner or a wooden dummy or kicking a tire is pretty simple to set up.

In both cases, however, you're talking about a process of years of training to remodel bone, and even then there are limits - toughen your fists as much as you want, your metacarpal bones in your hand still can only take so much before they crack.

BUT...

For a lot of the cases of striking hard objects, you risk joint damage over time. Punches tend to suffer this the most, since knuckles are a joint, not a solid chunk of bone. Just like how bone remodels to deal with force, the joints will start building up calcium deposits... and then you can't move as well at all.

So... for striking? Pretty much unless it's forearms/shins, you're probably losing rather than gaining. And even then, it's about consistent force over years of training, not "hitting harder" and trying to destroy objects as place where you see benefit. Otherwise, just go with resistance training.

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    Great answer. I will point out that many people willingly make the trade of potential joint damage for the ability to hit harder, especially because many of the serious problems show up only when practitioners get older. – mattm Nov 21 '15 at 22:05
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    I refuse the assumption that only increasing the bone density results in "hability to hit harder" . or that is the most effective and safe way to do so. Will post an answer on that – Freedo Nov 23 '15 at 17:51
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    I will add that when the average life expectancy was 40 years, you didn't worry about what your joints were like at 50. Those old school martial artists trained they way they did because they (a) were fighting for their lives, and (b) didn't expect to live long enough that the long term damage would be an issue. With the longevity that people enjoy today, the issues of long term damage are important to consider. – pojo-guy Jan 7 '16 at 4:36
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    ^this is a myth. Life expectancy wasn't really ever 40, but average life length was 40~ mostly because of the large amount of deaths in childbirth. If you lived to 40, even in the past, you were probably going to live to 70~. – Kyle Baker Dec 9 '18 at 2:49
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Yes, hitting objects does make your bones more solid.

Bones are primarily made up of two parts, and outer layer and an inner layer. The outer is a thin layer of compact bone (cortical bone). The inner layer is far less compact and is known as spongy or cancellous bone.

cancellous bone(hip)

The thin layer provides up to 80% of the strength of the bone despite covering a much smaller area.

Impact (hitting) will cause the density of the bones to increase. The outer layer will thicken and the inner layer will become denser. On impacts, tiny cracks are caused in the bone and when healed they are denser than before. This is not limited to impacts but also occurs under stress, lifting and twisting.

Those with weak bones are often told to exercise and specifically do light impact movements, such as jumping.

In traditional kung-fu, hand hardening exercises were part of daily routines, and done in such a way to gradually increase bone density without causing damage.

Modern boxers regularly suffer broken hands after punching forehands or hips, despite wearing gloves. This is mostly due to exercising only on soft pads/bags.

Additional Info:

There are quite a lot of medical papers which focus on bone strengthening. One example, which is quite accessible to non-medics, can be found at: http://www.springer.com/cda/content/document/cda_downloaddocument/9783642023996-c1.pdf (requires PDF reader).

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    Please quote from the citation(s) you listed that support the claim that martial arts practices of beating against the bone causes bone density increases in the short or long term. It's not enough just to cite the source paper in its entirety. – Steve Weigand Nov 23 '15 at 20:38
  • The paper you cited doesn't support your claim - it only states that microdamaged bone is replaced with "mechanically stronger bone to help preserve bone strength", not that the new bone is stronger than undamaged bone. – brazofuerte Feb 10 at 12:05
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I'll focus my answer on why you want to do that, and if it's an effective/safe way to achieve the goals that you are truly seeking (because even if you can increase your bone density, this does not necessarily mean that you achieve the goal you want).

I'll work with 3 scenarios:

  • I want to hit my opponent harder

  • I want to feel less pain

  • I want to prevent broken bones

I want to hit my opponent harder

First of all, you should focus on learning and executing the correct technique. You can have all the bone density you want, but a correctly executed strike will be much more effective and "harder" than a poorly executed strike. Training to achieving speed and correct technique should be much more important in your training routine than increasing your bone density.

Secondly, it's not the weight or the strength of your bones that results in a powerful punch, but the body weight, technique, and MUSCLE. If you have 10 kg of muscle on your arm, you may be able to hit a wall after years of training and not break your hand. However, if I have 30 kg of muscle on my arm, I can knock you out without the tedious and painful time spent hitting a wall. If you want to hit harder, hit the gym, build some muscle, and learn how to use your body weight in your favor.

Thirdly, know where to hit, and how to use speed and body weight to hit gracefully. Learning where it hit is down to you, your instructor, and your martial art, so I won't expand on this much. You don't need super strength to hurt (or even kill) someone; you just need to know where to hit them.

A few more tips:

  • Your strongest punch doesn’t land when your arms are fully out-stretched; your punch hits harder when it lands a bit shorter than your full range of motion.

  • Getting hit by a counter-punch hurts more than anything else.

  • Exhale sharply on every punch.

  • Body rotation, body rotation, body rotation. A full rotation with short arm extension hits harder than a small rotation with full arm extension.

In conclusion, hitting a wall or other hard, immovable object, doesn't make any sense if your goal is to "hit harder"; the ability to hit hard is the result of good technique, having muscle, creating impulse and speed, and knowing where to hit. Remember that essentially, mass (m) times (v) velocity equals impact power.

I want to feel less pain

There is already a very good question about this here on Martial Arts. Indeed one of the symptoms of osteoporosis is pain. But the bones are not where you feel pain. You feel pain on the nerves. And pain is not a physical thing, it happens only inside your head. Control your mind and you control your pain.

At same time, you can become desensitized to the pain if it's regular; your body learns to ignore it and you feel less and less pain, and at same time it grows stronger, not just the bones, but the nerves, the muscles, everything!

From personal experience, I had a lot of pain when practising some Krav Maga moves, especially immobilization, but I kept training and every day the pain decreased. Was it because of increased bone density? I doubt it, because it's an exercising with minimal direct impact on your bones (can't say the same for your joints). I only become desensitized about the pain, and acquired more flexibility so the range of motion didn't hurt as much.

There is little research on this subject, so I can't prove that increased bone density means less pain, but even if they researched this it would be difficult to prove that isn't just desensitization or muscle adaptation.

So, the best I can say to you is if you want to feel less pain, then feel the pain! Feel the pain with all your being, feel it on every cell, recognize that it's merely a warning of your body and that it will pass eventually.

While the same exercises that supposedly increase your bone density are the same that will help you to overcome the pain, it isn't possible to prove a direct link between the two. It would be very hard for any scientist to isolate the conditions and the biological adaptations that occur at all levels (plus pain can't be really measured).

So, just pick something to hit and keep hitting it, or do whatever is causing you pain and do it, but don't go to extremes thinking that opening micro-holes in your bones will help you in anything and give you time to rest! You will see that eventually the pain will decrease (if you have any medical condition, or are feeling extreme pain while or after doing this, stop immediately and seek professional help; you might have gone too far).

I want to prevent broken bones

This one is tricky. While increased bone density make bones stronger, it also make them less flexible. So it's a question of balance. Too low bone density and your bones will crack like glass; too much bone density and your bones cannot bend and will crack too.

The scientific evidence on low bone density and broken bones is very well documented [1]. The scientific evidence on high density and fractures is also very well documented; when the bone density is very high, it is usually associated with some sort of disease or illness and bone density is not equal to bone strength ([2] and [4]).

The scientific evidence on the risks of punching hard objects for a long time is scarce and as such, I cannot guarantee that it is safe or unsafe, or effective at all. So, why risk it?

However, I would reiterate that the majority of people break bones punching because of bad technique. My instructor reminds us all of the time of the importance of having good technique to avoid breaking your hand; some people above my grade already broke their hands because they were doing it wrong.

Technique is always everything! If in doubt, ask your instructor how to punch properly and practice that, repeatedly. This is a much better advice to prevent broken bones than "pick a wall, put some news papers, and hit it 20 times every day" because no matter how strong your bones are, if you are punching the wrong way, you will break your hand.

You may also be interested to see what you can do to strengthen your hands and wrists with weights; you may be surprised how weak your hands, fingers, and wrists are if you have never worked them before. Hand and wrist exercises really helped me with my martial arts, possibly more effectively and safely than hitting a wall. I won't include the specific exercises here, because my answer is already very long. I hope this helps and answers what you truly wanted to know behind your question.

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Well it seems I might be the only one who thinks this is mostly a myth. I'm open to the possibility that bone density can be changed by beating against the bone or breaking the bone, but I'll require citations for that from scientific sources first.

I wrote about this particular issue in my answer to the broader question of: Arm Toughening Without Losing Sensitivity

Quoting the relevant bits from my answer...

... 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.

Hope that helps.

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  • I added a link to a paper discussing micro-fractures in my answer above. – Taylor Taff Nov 23 '15 at 14:16
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    I had a chance to briefly scan the medical paper you cited in your answer. My tentative conclusion (correct me if I missed it) is that it describes how bone is normally formed and then covers diseases and conditions that affect bone growth. It doesn't seem to cover this particular claim: that bone density is increased through martial arts practices that beat against the bone. It talks about fractures and how the bone heals, but it doesn't seem to deal with the added question of how that affects density of the bone in the long term. Please add a quote that deals with this issue, if you can. – Steve Weigand Nov 23 '15 at 20:33
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    @mattm Yes, that's a well known phenomenon which I mentioned in my answer regarding Wolfe's Law. Any increase of load on your system will have the effect of increasing bone density. Weightlifting is a good example. But even just walking or running will have a similar effect. The reason for osteoporosis in old age is often because of being sedentary. Exercise can strengthen bones. Tennis will work. But it's not the same as beating your bones like some forms of martial arts do. That practice is what is questionable, not loading. – Steve Weigand Dec 6 '15 at 3:43
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    That's hugely different. That is load. That's not directly pounding the bone like what martial arts does. The way martial arts stuff is supposed to work is that there are microfractures that take place to the bone as a direct result of impact force on the bone. The way tennis and other sports, including just plain walking, work is that they're adding load forces to the bone. The bone has cells in it that respond to the load, secreting structures that build bone and make it more dense. It's not the same as repair after microfracture. – Steve Weigand Dec 6 '15 at 6:58
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    Hironiri Ohtsuka Sr. was an orthopedic surgeon, and founder of the Wado school of karate. He felt strongly enough about this that he formally removed a lot of the traditional impact exercises that damaged bone from his system, as useless training that harmed the body. Sorry, I have nothing to back this up except oral history. – pojo-guy Jan 7 '16 at 4:43
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Meta: Definitive hand conditioning answer?


According to the following study, practice of karate-style conditioning does lead to increased size of the metacarpals and hypertrophy of the skin over the knuckles, but it is also heavily associated with decreased wrist mobility and blood flow:

Kicking and Striking Objects

...

Roback5 studied 16 male and 4 female karateists and found that few injuries were reported from breaking objects, However, he found beneficial adaptive changes, such as enlargement of the second (35%), third (45%), and fourth (15%) metacarpals. Twenty percent also had thickening of the soft tissue of the little finger border of the palm and hypertrophy of the skin over the knuckles. Forty percent of the hands had mild abnormalities, 66% had decreased movement of the wrist, and 48% had decreased blood flow of the artery on the little finger side of the palm.

...

5. Roback MD: The injury debate. Black Belt Magazine. January 1979. pp 38-40

Note however that though it is oft-claimed that the bone which replaces micro-fractured bone in the body is 'stronger/harder/tougher' than healthy bone, this is not the case - it is only stronger than the damaged bone:

Bone constantly undergoes modeling (reshaping) during life to help it adapt to changing biomechanical forces, as well as remodeling to remove old, microdamaged bone and replace it with new, mechanically stronger bone to help preserve bone strength.


Further reading:

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  • Thanks. Very useful and definitive, especially in terms of sources – codezombie Feb 12 at 10:27
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Ignoring the answer that links to a completely irrelevant topic of fractures, rather than micro fractures (which is the equivalent of comparing bicep tears to tears in muscle fibers that cause muscle growth) it’s quite obvious that research shows bones do strengthen overtime from high impact.

Just think of it from a logical perspective. If you ever watch UFC or any type of kickboxing or Muay Thai there are vicious kicks and leg checks. Having experienced that, I can tell you that it’s extremely painful and it’s certainly possible to break your legs from a check.

So is it true that all kickboxers are naturally born with unbreakable legs? I guarantee you an average joe will snap their tibia in half of they kicked someone’s leg with a kickboxers amount of force. Obviously the kickboxers strengthened their shins over time. And I can also tell you I can kick harder objects with significantly more force than I could before I started training my shins. Five years ago I would’ve broken my leg on a heavy bag kick that I do now daily.

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