I'm fascinated by the athletic side of all of this. I have a friend who has had the aspiration to become a regular exerciser for years, but he says everything

I'm fascinated by the athletic side of all of this. I have a friend who has had the aspiration to become a regular exerciser for years, but he says everything he tries just hurts too much. I exercise regularly myself, but we haven't found a way to talk about it, because it's so hard to share subjective sensations of pain. In some sense, everything I do hurts, too, and everyone who works out or plays a sport acknowledges a lot of pain. People differentiate routine pain from pain that requires effort to endure and distinguishes both of those from pain that indicates an injury happening or being aggravated, and people value and hone their ability to distinguish the second two from each other, because they don't want to get injured but also don't want to let pain hold them back from doing something that makes their body healthier and stronger. I've known people who have endured through pain and suffered terrible consequences from it. Five years ago, my wife's aunt loved to say "I'm a tough old bird," and she has since lost a leg unnecessarily, because she thought that having high pain tolerance was a viable alternative to going to a doctor. Now she's in a wheelchair and does everything the doctors say. Other people have had opposite experiences, where learning to disregard pain led to breakthroughs for them. One woman I know set a big triathlon PR a year after having a kid, and when people asked her how she was able to do that, she said, "After having a kid, the pain just wasn't a big deal to me anymore." She's big into the science, so I expected to hear something about hormones, but for her, her expanded pain tolerance was the entire explanation for her better performance. Personally, just doing normal exercise presents me with an incredibly rich variety of "painful" sensations and a lot of difficult decisions. Right now I have a nagging shoulder injury, and every time an exercise generates a "painful" sensation in my shoulder, I have to decide, is this reflective of something making this injury worse? better? neutral impact? Should I stop right away so I don't aggravate the injury, or should I do this exercise more often because it's stimulating the tissue in just the right way? There's so much said and written about it, but it often seems frustratingly tautological. You have to know what the sensations mean before you can figure out which words refer to which sensations.