Good topic. For the record, I do think most instructor-level black belts will be familiar with the external conditioning methods many of you have already described in some detail. But I don't believe these exercises are practiced to any reasonable level of proficiency. It's one thing to do it occasionally as part of your curriculum - it's quite another to actually practice it to the point that your 'blocks' can bring tears to another man's eyes. I had a sempai that I honestly feared to cross forearms with, since even a few minutes of practice with him would leave purple bruises up and down my blade area. I eventually would have to adapt and block isshinryu style with my muscle when working with him just to avoid further trauma across the bone. He once smashed a baseball bat into two with just a forearm thrust, which is a feat I've only seen a handful of times from men who were all superior martial artists.
In terms of withstanding blows, there's not much to be done beyond strengthening the midsection and some judicious hardening of the shins and forearms.
Well, you can do a bit more than that. Consider the various natural strengthening exercises in Goju-ryu karate using weights like the chishi or tan. Performed properly, the increased muscle coming from these exercises is greatly more flexible than those gained from modern bodybuilding regimens, and combined with correct stance training can allow
a Goju karateka to withstand and divert force much greater than fighters who don't use these methods. (Not being a style egotist, all styles have their pluses and minuses - this just happens to be one of Goju's strong suits.) It's a combination of raw power from your legs and abdomen, strength and flexibility from your shoulders and back, and the sense of gripping and chi expression from your head through your spine through your core through your feet and toes.
Also, consider the dynamic tension strength built by practice of sanchin. Mas Oyama of kyokushin fame was a big supporter of sanchin strength practice and he always maintained that sanchin was a key component of his imposing physicality. Uechi-ryu karate has a soft version of sanchin as does hung gar gung fu. If you go read the Dragon Times interview with Sensei Shinyu Gushi, he has a few interesting words to say about sanchin:
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I don't do any weight training. I used to do a little when I was young but Uehara sensei told me that it I should concentrate on the quality of my muscles and not just their size so I cut it down to a minimum. It's good to be strong but in karate it's speed and "snap" that you need. What muscles I have comes from Sanchin training and using nigiri game. Muscles developed this way serve to protect the body, weight training just produces a pleasing appearance.
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When you are fighting (drops into Sanchin stance) you pull your shoulders down like this and tense your muscles, including those around your throat to make a shield. With your body round and compact and your muscles tense you are relatively safe and protected. We pull everything into the center, lower our bodies like this and make them round and smooth. Techniques are performed in front of the body, we don't block above the level of the head for example because that would weaken our defenses."[/FONT]
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http://www.dragon-tsunami.org/Dtimes/Pages/article18.htm
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