The podcast is worth listening to, but I can summarize the key points:
- Pain is not as simple as: damage to the body ==> pain. For example, some people have back pain. Some of them, when examined with MRI's, have damage to parts of their spines (herniated discs, fractured vertebrae, etc.) It is easy to assume that the damage causes the pain. But when people who have no pain are picked off the street randomly and tested they often show very similar damage - but no pain at all.
- Pain is profoundly influenced by expectations and psychology (which is not the same as saying it's 'all in your head'). Take the placebo effect. Give someone a sugar pill but tell them it's a painkiller and they will often feel better - the pain goes away. Similarly, there is a nocebo effect - give someone a treatment that they think might have side effects and they might experience pain even if you're not actually doing anything to them.
- In short, a person's beliefs and expectations can influence whether or not they experience pain from a particular physical situation. There are probably physical states that are always painful (broken leg?) and some that are never painful, but there is a much wider range in the middle that might go either way.
None of which is to say you should ignore pain or encourage your students to do so (in the context that I think we all understand that there is a difference between the temporary, normal, and mild pain of muscular exertion and the pain of injury). Pain is often a real and important indicator of mechanical injury. Unless you're an orthopedist, if a student of yours is in injury-type pain I wouldn't suggest you do anything other than refer them to a physician.
But you should also understand that certain beliefs might make your students more likely to experience pain. And as an instructor or a fellow student, your words can have a profound impact on other people's beliefs and expectations.
Let me give a quick example. I played (American) football (poorly, but I was on the team) in high school. Everyone was hyper-aware of the risk of knee injury, and it was thought by most of us that almost all hard training was likely to cause long term knee damage. We all told each other this, and all believed it. We took it in stride (and some misguided pride) that playing football would give us all 'bad knees' eventually.
So my knees hurt. By my junior year I had constant low grade pain in my knees. Then I stopped practicing (my career ended), and the knee pain dissipated.
Did I have damage to my knees that healed? Was there some physical, mechanical abnormality in my knees in high school that went away? Perhaps. But I often did more and harder training (albeit of slightly different kinds) in later years and never had even a tiny amount of pain at any other point in my life, up to and including now. I have also never done any training since then that I believed would cause knee pain.
I'm pretty sure my expectations of getting 'bad knees' led to my knee pain in high school. It's hard to imagine another explanation for a pain that simply went away, without any intervention, never to return, even as I aged and did a lot of hard training later in life.
What is the point? If a student comes to you with a sharp pain, take it seriously. I would never suggest otherwise. HOWEVER there are things you can do during training that might prevent the pain from ever occurring.
When you teach proper form, it is (I think?) only natural to suggest to people that doing things incorrectly can lead to injury. Locking joints while striking, letting knees cave inwards in stances, etc. all put the body in compromising positions that can lead to injury.
The problem is that telling your students this makes it more likely that they'll experience those injuries (by the nocebo effect). Obviously, the right solution is NOT to avoid teaching proper form. But when teaching proper form, emphasize the non-injury-related aspects of that form. Teach your students to use proper alignment because it's more efficient, takes less energy, increases accuracy, or increases power. Or even because it looks better.
You should continue to demand that your students constantly improve their technical abilities, but you should probably emphasize all the reasons for this without talking about how it will make them less likely to get hurt. Because if you do, then when they realize their form isn't absolutely perfect (because almost nobody has perfect form), they might believe that their technique is hurting them - and that belief itself makes it more likely that it will.
Once again: Don't lie to your students. Don't ignore a student in pain or suggest that they ignore pain. Do teach proper movement to minimize the chances that your students get hurt. Do emphasize all the reasons for that proper movement EXCEPT the fact that it will minimize their risk of injury.