user-1: Both the Theravada and the Zen traditions appear to regard pain, even extreme physical pain, as a necessary part of sitting, whereas Ngakpa Chogyam in Journey into Vastness, speaking for the Dzogchen point of view, seems to imply that pain is an indication that one is not sitting properly and that there are ways of sitting that do not produce pain. 
The only references to pain in the context of meditation in the Pali Canon appear to refer to the Buddha's six-year period of self-mortification, which he repudiated (correct me with a specific reference if I am mistaken). Therefore, I am interested in the attitude of different Buddhist schools to pain in the context of sitting and meditation. Is it a sign of poor sitting practice or is it part of the experience, perhaps even something important that should be cultivated (e.g., ancient shamans used pain to induce altered states of consciousness, an example being the famous Sun Dance in which in which practitioners hung themselves by the pectoral muscles from a post for several days). 
What do the different Buddhist schools and traditions say about this?

user-1: My experience with Soto Zen is that, a first mention of pain during sitting is regarded as normal and one should "just keep doing it". Generally, there's also a culture within Soto Zen taking pride on painful things -- like hard blows of keisaku, or sleeping on hard wood -- but I suspect this is more related to novices then advanced practitioners.
At the same time, using a different posture or a chair was always welcomed -- despite the toughness attitude, meditation itself was more important than posture, specially if it's becoming an obstacle. My experience with Tibetan and Theravada is similar on this: there's a preference for a stable and "portable" position like lotus. But being in unbearable pain when meditating in a posture is not seeing as positive to the practice.
Also, westerns are notorious for having difficulties sitting cross legged and many monasteries of different schools offer cushions and chairs.
From the suttas, I think the attitude towards pain in the training depends on a few things:

whether the physical discomfort is optional (e.g. dwelling temperature, body position, hunger/thirst, etc) as opposed to medical condition.
whether the pain is present right now.
whether the hindrance of aversion is present.

There are some specific points to draw.
Training samatha, for example, is notoriously difficult under physical pain. Here's a section of a sutta that is indicative of the problem of physical discomfort to develop samadhi:

But with excessive thinking and pondering I might tire my body, and when the body is tired, the mind becomes strained, and when the mind is strained, it is far from concentration. So I steadied my mind internally, quieted it, brought it to singleness, and concentrated it. Why is that? So my mind should not be strained.
-- Dvedhāvitakka Sutta [Bodhi trans.], MN 19

I think understanding how pain is dealt with in general in the suttas might illuminate how one should approach it during sitting (or non-sitting) meditation.
The general teaching that I think most schools share towards pain is to be mindful of the pain being experienced. Here's an associated sutta section:

“There are, bhikkhus, tangible objects cognizable by the body that are agreeable and those that are disagreeable. One should train so that these do not persist obsessing one’s mind even when they are repeatedly experienced. When the mind is not obsessed, tireless energy is aroused, unmuddled mindfulness is set up, the body becomes tranquil and untroubled, the mind becomes concentrated and one-pointed”
-- SN 35.134

A more detailed technique is described in the sathipatana sutta in the contemplation of feeling section:

"And how, O bhikkhus, does a bhikkhu live contemplating feeling in feelings?
"Here, O bhikkhus, a bhikkhu when experiencing a pleasant feeling, understands: 'I experience a pleasant feeling'; when experiencing a painful feeling, he understands: 'I experience a painful feeling'; when experiencing a neither-pleasant-nor-painful feeling, he understands: 'I experience a neither-pleasant-nor-painful feeling'; when experiencing a pleasant worldly feeling, he understands: 'I experience a pleasant worldly feeling'; when experiencing a pleasant spiritual feeling, he understands: 'I experience a pleasant spiritual feeling'; when experiencing a painful worldly feeling, he understands: 'I experience a painful worldly feeling'; when experiencing a painful spiritual feeling, he understands: 'I experience a painful spiritual feeling'; when experiencing a neither-pleasant-nor-painful worldly feeling, he understands: 'I experience a neither-pleasant-nor-painful worldly feeling'; when experiencing a neither-pleasant-nor-painful spiritual feeling, he understands: 'I experience a neither-pleasant-nor-painful spiritual feeling.'
"Thus he lives contemplating feelings in feelings internally, or he lives contemplating feeling in feelings externally, or he lives contemplating feeling in feelings internally and externally. He lives contemplating origination-things in feelings, or he lives contemplating dissolution-things in feelings, or he lives contemplating origination-and-dissolution-things in feelings. Or his mindfulness is established with the thought: 'Feeling exists,' to the extent necessary just for knowledge and remembrance and he lives independent and clings to naught in the world.
"Thus, indeed, O bhikkhus, a bhikkhu lives contemplating feeling in feelings."
-- Satipatthana Sutta, MN 10 (Soma Thera Trans.)

Moreover, presence of pain is an opportunity to develop equanimity:

"Now how, Ananda, in the discipline of a noble one is there the unexcelled development of the faculties?
"[...] when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable & disagreeable. He discerns that 'This agreeable thing has arisen in me, this disagreeable thing... this agreeable & disagreeable thing has arisen in me. And that is compounded, gross, dependently co-arisen. But this is peaceful, this is exquisite, i.e., equanimity.' With that, the arisen agreeable thing... disagreeable thing... agreeable & disagreeable thing ceases, and equanimity takes its stance. Just as a strong man might easily extend his flexed arm or flex his extended arm, that is how quickly, how rapidly, how easily, no matter what it refers to, the arisen agreeable thing... disagreeable thing... agreeable & disagreeable thing ceases, and equanimity takes its stance. In the discipline of a noble one, this is called the unexcelled development of the faculties with regard to tactile sensations cognizable by the body.
"And how is one a person in training, someone following the way?
There is the case where, when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable & disagreeable. He feels horrified, humiliated, & disgusted with the arisen agreeable thing... disagreeable thing... agreeable & disagreeable thing.
"And how is one a noble one with developed faculties?
There is the case where, when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable & disagreeable. If he wants, he remains percipient of loathsomeness in the presence of what is not loathsome. If he wants, he remains percipient of unloathsomeness in the presence of what is loathsome. If he wants, he remains percipient of loathsomeness in the presence of what is not loathsome & what is. If he wants, he remains percipient of unloathsomeness in the presence of what is loathsome & what is not. If he wants — in the presence of what is loathsome & what is not — cutting himself off from both, he remains equanimous, alert, & mindful.
-- Indriya-bhavana Sutta, MN 152 (Thanissaro Trans.)

Endurance is an important part of the practice as well (Soto Zen is particularly emphatic on this one):

“Bhikkhus, in three cases ardor should be exercised. What three? (1) Ardor should be exercised for the non-arising of unarisen bad unwholesome qualities. (2) Ardor should be exercised for the arising of unarisen wholesome qualities. (3) Ardor should be exercised for enduring arisen bodily feelings that are painful, racking, sharp, piercing, harrowing, disagreeable, sapping one’s vitality. In these three cases ardor should be exercised.
-- AN 3.49

Finally, here's how the Buddha is described reacting to bodily pain:

Now on that occasion the Blessed One’s foot had been cut by a stone splinter. Severe pains assailed the Blessed One—bodily feelings that were painful, racking, sharp, piercing, harrowing, disagreeable. But the Blessed One endured them, mindful and clearly comprehending, without becoming distressed.
-- SN 1.38


Complementary, the presence of aversion is one of the 5 hindrances that generally obstruct one's practice:

“Bhikkhus, there are these five hindrances. What five? The hindrance of sensual desire, the hindrance of ill will [aversion], the hindrance of sloth and torpor, the hindrance of restlessness and remorse, the hindrance of doubt. These are the five hindrances. This Noble Eightfold Path is to be developed for direct knowledge of these five hindrances, for the full understanding of them, for their utter destruction, for their abandoning.”
SN 45.177


user-1: Theravada Buddhist Answer. Vipassana instructions following the tradition of the late Ven. Mahasi Sayadaw.
The body is conditioned and therefore "dukkha". There will arise pain sooner or later in one form or the other. That is its nature.
Pain is just pain. There is nothing inherently bad about it. It's simply an experience.
In the Sallatha Sutta (SN 36.6) the Buddha compared pain and our reaction to the pain as being shot by 2 arrows.
The first arrow is the pain we cannot avoid, e.g. physical pain from doing sitting meditation. The second arrow is our aversion (attachment) to the pain. This arrow we can avoid by being mindful and taking the pain as an object of meditation.
In Vipassana meditation pain should be observed with mindfulness in the present moment. If aversion to the pain arises, then the aversion should be taken as an object. 
This allows us to see the object clearly and thereby change the reactionary behavior of the untrained mind into a behavior based on impartiality and acceptance of what is ocurring at the sense doors.

user8157: Pain is obviously related to physical posture; obviously related to the mobility of an individual's body & joints. Therefore, some individuals without any samadhi (meditative development) can sit for long periods while other individuals (who might have better samadhi) cannot sit as long without experiencing pain. 
For example, in the West, are often found slender naturally flexible women leading hatha yoga classes, who display no evidence of spiritual development (e.g., they are emotionally unbalanced, addicted to cigarettes, etc).
Imo, the above shows there is no relevance or correlation between physical posture/pain and meditative development. If it was otherwise, a naturally physically flexible person would either be advantaged or disadvantaged compared to another person. 
When samadhi (concentration) is genuinely developed (absorption into breathing, jhana, etc), awareness of pain disappears from consciousness, even though the legs themselves may become very stiff & very painful. A samadhi practitioner may sit for a few hours without consciously experiencing pain then, after emerging from samadhi, will struggle to stand up & walk. 
This is why I am not aware of any instructions in the Pali teachings about meditation & physical pain. In fact, the very essence of the Middle-Way is the development of jhana (with rapture, happiness & equanimity) which is contrary to those Theravada schools (Goenka; Mahasi, etc) that teach meditation on pain. 
Since the ultimate purpose of Buddhist meditation is to develop a bliss (samatha) that liberates an individual from reliance on sensuality & then insight (vipassana) that liberates a individual from attachment, self-view & suffering, it is obvious meditation on pain is not directly relevant to the Buddhist path.
When I was young, I practised meditation very intensively and developed some capacity to be non-attached. Then at a later time, my body suffered an injury & a lengthy rehabilitation that was very painful at times. I required no additional training in non-attachment to deal with my injury & rehabilitation. The non-attachment developed in my painless meditation, when I was younger, was more than sufficient. 
It may sound like a paradox but non-attachment & dispassion towards rapture (piti) is said by some to be much more effective at dealing with pain that direct meditation on pain itself. This is probably why the Buddha encouraged the development of non-attachment & egolessness (rather than meditation on pain itself).

-1: <p>Both the Theravada and the Zen traditions appear to regard pain, even extreme physical pain, as a necessary part of sitting, whereas Ngakpa Chogyam in <em>Journey into Vastness</em>, speaking for the Dzogchen point of view, seems to imply that pain is an indication that one is not sitting properly and that there are ways of sitting that do not produce pain. </p>

<p>The only references to pain in the context of meditation in the Pali Canon appear to refer to the Buddha's six-year period of self-mortification, which he repudiated (correct me with a specific reference if I am mistaken). Therefore, I am interested in the attitude of different Buddhist schools to pain in the context of sitting and meditation. Is it a sign of poor sitting practice or is it part of the experience, perhaps even something important that should be cultivated (e.g., ancient shamans used pain to induce altered states of consciousness, an example being the famous Sun Dance in which in which practitioners hung themselves by the pectoral muscles from a post for several days). </p>

<p>What do the different Buddhist schools and traditions say about this?</p>
 -1: <p>My experience with Soto Zen is that, a first mention of pain during sitting is regarded as normal and one should &quot;just keep doing it&quot;. Generally, there's also a culture within Soto Zen taking pride on painful things -- like hard blows of keisaku, or sleeping on hard wood -- but I suspect this is more related to novices then advanced practitioners.</p>
<p>At the same time, using a different posture or a chair was always welcomed -- despite the toughness attitude, meditation itself was more important than posture, specially if it's becoming an obstacle. My experience with Tibetan and Theravada is similar on this: there's a preference for a stable and &quot;portable&quot; position like lotus. But being in unbearable pain when meditating in a posture is not seeing as positive to the practice.</p>
<p>Also, westerns are notorious for having difficulties sitting cross legged and many monasteries of different schools offer cushions and chairs.</p>
<p>From the suttas, I think the attitude towards pain in the training depends on a few things:</p>
<ul>
<li>whether the physical discomfort is optional (e.g. dwelling temperature, body position, hunger/thirst, etc) as opposed to medical condition.</li>
<li>whether the pain is present right now.</li>
<li>whether the hindrance of aversion is present.</li>
</ul>
<p>There are some specific points to draw.</p>
<p>Training samatha, for example, is notoriously difficult under physical pain. Here's a section of a sutta that is indicative of the problem of physical discomfort to develop samadhi:</p>
<blockquote>
<p>But with excessive thinking and pondering I might <strong>tire my body, and when the body is tired, the mind becomes strained, and when the mind is strained, it is far from concentration</strong>. So I steadied my mind internally, quieted it, brought it to singleness, and concentrated it. Why is that? So my mind should not be strained.</p>
<p>-- Dvedhāvitakka Sutta [Bodhi trans.], <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.019.than.html" rel="nofollow noreferrer">MN 19</a></p>
</blockquote>
<p>I think understanding how pain is dealt with in general in the suttas might illuminate how one should approach it during sitting (or non-sitting) meditation.</p>
<p>The general teaching that I think most schools share towards pain is to be mindful of the pain being experienced. Here's an associated sutta section:</p>
<blockquote>
<p>“There are, bhikkhus, tangible objects cognizable by the body that are agreeable and those that are disagreeable. One should train so that these do not persist obsessing one’s mind even when they are repeatedly experienced. When the mind is not obsessed, tireless energy is aroused, unmuddled mindfulness is set up, the body becomes tranquil and untroubled, the mind becomes concentrated and one-pointed”</p>
<p>-- <a href="https://suttacentral.net/en/sn35.134" rel="nofollow noreferrer">SN 35.134</a></p>
</blockquote>
<p>A more detailed technique is described in the sathipatana sutta in the contemplation of feeling section:</p>
<blockquote>
<p>&quot;And how, O bhikkhus, does a bhikkhu live contemplating feeling in feelings?</p>
<p>&quot;Here, O bhikkhus, a bhikkhu when experiencing a pleasant feeling, understands: 'I experience a pleasant feeling'; when experiencing a painful feeling, he understands: 'I experience a painful feeling'; when experiencing a neither-pleasant-nor-painful feeling, he understands: 'I experience a neither-pleasant-nor-painful feeling'; when experiencing a pleasant worldly feeling, he understands: 'I experience a pleasant worldly feeling'; when experiencing a pleasant spiritual feeling, he understands: 'I experience a pleasant spiritual feeling'; when experiencing a painful worldly feeling, he understands: 'I experience a painful worldly feeling'; when experiencing a painful spiritual feeling, he understands: 'I experience a painful spiritual feeling'; when experiencing a neither-pleasant-nor-painful worldly feeling, he understands: 'I experience a neither-pleasant-nor-painful worldly feeling'; when experiencing a neither-pleasant-nor-painful spiritual feeling, he understands: 'I experience a neither-pleasant-nor-painful spiritual feeling.'</p>
<p>&quot;Thus he lives contemplating feelings in feelings internally, or he lives contemplating feeling in feelings externally, or he lives contemplating feeling in feelings internally and externally. He lives contemplating origination-things in feelings, or he lives contemplating dissolution-things in feelings, or he lives contemplating origination-and-dissolution-things in feelings. Or his mindfulness is established with the thought: 'Feeling exists,' to the extent necessary just for knowledge and remembrance and he lives independent and clings to naught in the world.</p>
<p>&quot;Thus, indeed, O bhikkhus, a bhikkhu lives contemplating feeling in feelings.&quot;</p>
<p>-- Satipatthana Sutta, <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.010.soma.html" rel="nofollow noreferrer">MN 10</a> (Soma Thera Trans.)</p>
</blockquote>
<p>Moreover, presence of pain is an opportunity to develop equanimity:</p>
<blockquote>
<p>&quot;Now how, Ananda, in the discipline of a noble one is there the unexcelled development of the faculties?</p>
<p>&quot;[...] when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable &amp; disagreeable. He discerns that 'This agreeable thing has arisen in me, this disagreeable thing... this agreeable &amp; disagreeable thing has arisen in me. And that is compounded, gross, dependently co-arisen. But this is peaceful, this is exquisite, i.e., equanimity.' With that, the arisen agreeable thing... disagreeable thing... agreeable &amp; disagreeable thing ceases, and equanimity takes its stance. Just as a strong man might easily extend his flexed arm or flex his extended arm, that is how quickly, how rapidly, how easily, no matter what it refers to, the arisen agreeable thing... disagreeable thing... agreeable &amp; disagreeable thing ceases, and equanimity takes its stance. In the discipline of a noble one, this is called the unexcelled development of the faculties with regard to tactile sensations cognizable by the body.</p>
<p>&quot;And how is one a person in training, someone following the way?</p>
<p>There is the case where, when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable &amp; disagreeable. He feels horrified, humiliated, &amp; disgusted with the arisen agreeable thing... disagreeable thing... agreeable &amp; disagreeable thing.</p>
<p>&quot;And how is one a noble one with developed faculties?</p>
<p>There is the case where, when touching a tactile sensation with the body, there arises in a monk what is agreeable, what is disagreeable, what is agreeable &amp; disagreeable. If he wants, he remains percipient of loathsomeness in the presence of what is not loathsome. If he wants, he remains percipient of unloathsomeness in the presence of what is loathsome. If he wants, he remains percipient of loathsomeness in the presence of what is not loathsome &amp; what is. If he wants, he remains percipient of unloathsomeness in the presence of what is loathsome &amp; what is not. If he wants — in the presence of what is loathsome &amp; what is not — cutting himself off from both, he remains equanimous, alert, &amp; mindful.</p>
<p>-- Indriya-bhavana Sutta, <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.152.than.html" rel="nofollow noreferrer">MN 152</a> (Thanissaro Trans.)</p>
</blockquote>
<p>Endurance is an important part of the practice as well (Soto Zen is particularly emphatic on this one):</p>
<blockquote>
<p>“Bhikkhus, in three cases ardor should be exercised. What three? (1) Ardor should be exercised for the non-arising of unarisen bad unwholesome qualities. (2) Ardor should be exercised for the arising of unarisen wholesome qualities. (3) Ardor should be exercised for enduring arisen bodily feelings that are painful, racking, sharp, piercing, harrowing, disagreeable, sapping one’s vitality. In these three cases ardor should be exercised.</p>
<p>-- <a href="https://suttacentral.net/en/an3.49" rel="nofollow noreferrer">AN 3.49</a></p>
</blockquote>
<p>Finally, here's how the Buddha is described reacting to bodily pain:</p>
<blockquote>
<p>Now on that occasion the Blessed One’s foot had been cut by a stone splinter. Severe pains assailed the Blessed One—bodily feelings that were painful, racking, sharp, piercing, harrowing, disagreeable. But the Blessed One endured them, mindful and clearly comprehending, without becoming distressed.</p>
<p>-- <a href="https://suttacentral.net/en/sn1.38" rel="nofollow noreferrer">SN 1.38</a></p>
</blockquote>
<hr />
<p>Complementary, the presence of aversion is one of the 5 hindrances that generally obstruct one's practice:</p>
<blockquote>
<p>“Bhikkhus, there are these five hindrances. What five? The hindrance of sensual desire, the hindrance of ill will [aversion], the hindrance of sloth and torpor, the hindrance of restlessness and remorse, the hindrance of doubt. These are the five hindrances. This Noble Eightfold Path is to be developed for direct knowledge of these five hindrances, for the full understanding of them, for their utter destruction, for their abandoning.”</p>
<p><a href="https://suttacentral.net/en/sn45.177" rel="nofollow noreferrer">SN 45.177</a></p>
</blockquote>
 -1: <p><em>Theravada Buddhist Answer. Vipassana instructions following the tradition of the late Ven. Mahasi Sayadaw.</em></p>

<p>The body is conditioned and therefore "dukkha". There will arise pain sooner or later in one form or the other. That is its nature.</p>

<p>Pain is just pain. There is nothing inherently bad about it. It's simply an experience.</p>

<p>In the <a href="http://www.accesstoinsight.org/tipitaka/sn/sn36/sn36.006.nypo.html" rel="nofollow"><em>Sallatha Sutta (SN 36.6)</em></a> the Buddha compared pain and our reaction to the pain as being shot by 2 arrows.</p>

<p>The first arrow is the pain we cannot avoid, e.g. physical pain from doing sitting meditation. The second arrow is our aversion (attachment) to the pain. This arrow we can avoid by being mindful and taking the pain as an object of meditation.</p>

<p>In Vipassana meditation pain should be observed with mindfulness in the present moment. If aversion to the pain arises, then the aversion should be taken as an object. </p>

<p>This allows us to see the object clearly and thereby change the reactionary behavior of the untrained mind into a behavior based on impartiality and acceptance of what is ocurring at the sense doors.</p>
 8157: <p>Pain is obviously related to physical posture; obviously related to the mobility of an individual's body &amp; joints. Therefore, some individuals without any samadhi (meditative development) can sit for long periods while other individuals (who might have better samadhi) cannot sit as long without experiencing pain. </p>

<p>For example, in the West, are often found slender naturally flexible women leading <em>hatha yoga</em> classes, who display no evidence of spiritual development (e.g., they are emotionally unbalanced, addicted to cigarettes, etc).</p>

<p>Imo, the above shows there is no relevance or correlation between physical posture/pain and meditative development. If it was otherwise, a naturally physically flexible person would either be advantaged or disadvantaged compared to another person. </p>

<p>When <em>samadhi</em> (concentration) is genuinely developed (absorption into breathing, jhana, etc), awareness of pain disappears from consciousness, even though the legs themselves may become very stiff &amp; very painful. A samadhi practitioner may sit for a few hours without consciously experiencing pain then, after emerging from samadhi, will struggle to stand up &amp; walk. </p>

<p>This is why I am not aware of any instructions in the Pali teachings about meditation &amp; physical pain. In fact, the very essence of the Middle-Way is the development of jhana (with rapture, happiness &amp; equanimity) which is contrary to those Theravada schools (Goenka; Mahasi, etc) that teach meditation on pain. </p>

<p>Since the ultimate purpose of Buddhist meditation is to develop a bliss (<em>samatha</em>) that liberates an individual from reliance on sensuality &amp; then insight (<em>vipassana</em>) that liberates a individual from attachment, self-view &amp; suffering, it is obvious meditation on pain is not directly relevant to the Buddhist path.</p>

<p>When I was young, I practised meditation very intensively and developed some capacity to be non-attached. Then at a later time, my body suffered an injury &amp; a lengthy rehabilitation that was very painful at times. I required no additional training in non-attachment to deal with my injury &amp; rehabilitation. The non-attachment developed in my painless meditation, when I was younger, was more than sufficient. </p>

<p>It may sound like a paradox but non-attachment &amp; dispassion towards rapture (<em>piti</em>) is said by some to be much more effective at dealing with pain that direct meditation on pain itself. This is probably why the Buddha encouraged the development of non-attachment &amp; egolessness (rather than meditation on pain itself).</p>
