Getting back on my bicycle the last few weeks I initially had some knee pain. It was not major pain, but it was enough to make me feel uncomfortable. Great, knee pain from cycling and leg pain from running. This contributed to some of the negatively the last few weeks. I wondered, 'knee pain? from biking?' However, I quickly remembered when I had had similar knee pain from biking many years ago, it was because my seat was too low. So I took out my little torque wrench and adjusted my bicycle for the first time in three years I think, and raised the seat about 4 millimeters. Having done over 100 miles since then, I assume that raising the seat because my legs are longer is what I needed. I realize it's not a lot, but I'm 28 years old!
Our bodies are amazing things. We really don't understand them. We're attempting to map the human brain, but at every step of the way we are finding it is more complex than we originally thought. There are tens of billions of neurons in a human brain, and they don't all work the same in every person, from what we know so far. For example, if you are missing part of your brain you can train your brain to take on some of the functions of the missing part.
The point being, the physical experiment that is my body continues to amaze me.