The human knee corresponds to a door hinge.
It bends in only one axis with very little side compliance.
Whatever side compliance we think we have in our knee actually comes from our hip, ankle and foot.
When we feel pain in our knee, it comes as the result of how we use our foot, ankle and hip, with some pain coming from over-dependence on our front thigh muscles to mash the pedal down.
Most Americans walk with their toes out.
One can check this most accurately by observing his or her wet footprints on the floor.
If a person walks with his toes out, he does so because of the way he organizes the movement of his hips, ankles and feet.
Transferring this walking-organization to a bicycle spin means one puts side loads on his knee; a joint not intended to take side loads.
How to have happy knees:
Stand with your feet straight ahead.
When straight ahead, your feet may feel pointed inwards.
Put your hands on your back trouser pockets so you can feel the muscles in your outer buttocks and hips.
Slowly step backwards and place your foot one pace backwards and perfectly straight.
Do it slowly and pay attention.
Put the foot down perfectly straight.
Walk backwards in this manner for several paces, paying attention to how the muscles in the hips must work in order to put your foot down straight.
In order to put your foot down straight, with your toes relatively in compared to your normal walk and stance, you will need to turn your heel out; and, in order to turn your heel out you will need to do something different with your hip muscles.
Try the above before reading any further.
I'll wait....
Now we need to transfer this to the bicycle.
Usually, one knee hurts and not the other.
If they both hurt use the same technique on both of them.
In the spin, as the foot goes forward and down, visualize turning the heel out and the toe in, as if stepping on something and squishing it, like a bug or a cigarette.
More than the toe going in, the heel should go out.
This happens in the hip.
One can help this by simultaneously pushing sidewards with the foot as it goes down.
So, as the foot goes forward and down, push sidewards/outwards with the foot and visualize the toe going in and the heel going out, with the emphasis on the heel going out.
When one does this right, it will cause the knee to come in towards the top tube, so that sometimes the knee will actually graze the top tube.
If one put lights on his knees, so that he could see their up and down path using this method, they might look like the following parentheses symbols )(
Not so exaggerated, though.
In fact, to someone riding behind you, your knees should just go up and down !! and not inward )(
However much it may feel as if your toe and knee go in and your heel goes out, an observer behind you will just see straight up and down knees and a straight ahead foot.
Got all that?
OK.
One more thing.
As the foot goes down and forward, push lightly outwards with the foot, a little bit of toe in and a lot of heel out - AND - roll the foot and ankle inwards so that at the bottom of the spin, as one stands on the pedal, his weight goes into the pedal through the big toe and the index toe.
When your knee hurts, do the above and the pain will go away within seconds.
Then you forget to do it and the pain will come back.
Then you will remember to do it and the pain will go away.
This yo-yo goes on for about a year of riding before one does it all the time and has no pain.
I ride in a rolling hill urban and suburban environment, with about 1000 feet of dynamic range; meaning, I gain or lose 1000 feet on a typical ride.
At 59 years of age, I ride with a 53t chainring and a17t cog for 81.9 gear inches.
I have no knee pain.
I have HAD knee pain in the past, but I don't have it now, riding my bike.
I sometimes have knee pain when walking, and I practice the things I do in my spin with my walking, and the walking pain goes away, instantly.
I have more to say on this subject, especially regarding subconscious mashing, but I'll wait to see if anyone has any interest in what I have already written.
I love this subject.
I think about it all the time.
I intend to eventually produce a DVD addressing knee pain.
I'll sell it at cost.
I just want people to enjoy riding their bike.
By the way, I don't know anything about toes-in issues.
For those who walk with their toes in, I don't have any corrective techniques, yet.