Dipping into the mailbag (well, "comment bag"):
What would you do about intermittent and unpredictable pain? Mine started after a mild injury last winter. I got a clean bill of health from a doctor and got on with physio, which helped enough.
But recently I've been getting bouts of pain and swelling, which your blog has helped me to recognize are probably delayed onset pain from activities. I like walking and swimming anyway so I decided to follow your methods. The issue I'm having is that a walk of, say 5km, can be fine one week and agonizing the next. I'm struggling to develop and keep to any plan because it all just feels so unpredictable.
This is a great question, because it's a hard one, and also so common (especially for people who are desperately seeking to remain active).
So, in a nutshell, if you're an active person struggling to overcome knee pain, the situation can look something like this:
One day, you notice you have knee pain. Over the next few weeks, you try to ignore it. But it doesn't go away. Frustrated, you finally decide to curtail your activities. You settle on something like "I'll walk 5,000 steps a day. That's nothing! I'm used to doing so, so much more! But I'll just do the 5,000 steps for a while, build up my knees and maybe leg muscles too, then increase my walking. And then, after some months, I'll be healed!"
But then: Ugh. You do your 5,000 steps each day and the results are decidedly mixed. You have some good days. But there are bad days mixed in, and you're not quite sure why. You flounder about, growing more frustrated. What's going on? You know you're fit enough. You should be able to walk 10,000 steps a day, no problem. Gradually, you start to lose hope ...
In this case, "Intermittent Pain" is getting "pain and swelling" ... and the results of walking some distance can be fine one week and "agonizing the next."
So here are some thoughts (and again, not advice, but things to consider):
1. A couple of scary words in Intermittent Pain's account are "swelling" and "agonizing." This sounds like what would be expected from someone with a weak joint who is doing too much.
Even though some weeks are "fine," my inclination would be to worry I'm playing around a little too close to the edge of what my knee can tolerate. This reminds me of when I got a leave from my job in Hong Kong because of my bad knees and, convinced that they really needed movement, proceeded to drown them in easy movement. And I got worse.
My real "ah hah" moment came on realizing my knees were a lot weaker than I initially thought. That's when I scaled way, way back on my walking. This can be very, very hard to do for active people who are used to biking or running or hiking for hours and hours every week. But when I scaled way, way back, I was able to find a new baseline, then start to improve from that.
2. Another thing that can be useful is trying to keep notes on what's happening on the bad knee days. Do they typically fall on days when you have to sit a lot the day before? Do they come after you eat certain foods? In certain weather? I would hoover up details, jot them down, and see if I can detect patterns.
3. I don't know what the mild injury you sustained was, but might it be worth going back to the doctor (or seeing another doctor) to make sure there's no lingering issue (or new issue) that could be causing problems? There always could be something structurally wrong that needs attention.
4. You mention you like swimming. That's wonderful (and typically a great activity for bad knees). If I were you, I might think about spending as much time in the pool as I can, and as little time walking about on land as possible, when it comes to getting my exercise in.
That's all from me! Readers of this blog may have other thoughts. Good luck!