What kind of muscle/joint/ligament do walking upstair/downstair involve?

Question

I tried to understand why walking downstair hurts while walking upstair is good. All I found in the internet were website while keep saying the pointless fact "It's runner's knee" and didn't try hard to explain why except telling you may have a feet in bad shape.

I think the knowing of the kind of muscle/joint/ligament involved during walking upstair/downstair might help understanding the cause of the pain.

From my personal experience, I trained my quadriceps by squating and my pain goes away temporarily. If I let my quadriceps relax for 2-3 weeks and try to run, my pain comes back. So I think it must related to the muscle.

Answer 1

The muscles involved in going down stairs are the same as when going up, but they are being used differently. The primary difference is that instead of your quadriceps pushing you up (a concentric contraction), your quad is resisting gravity as it lowers your body down (an eccentric contraction). The eccentric contraction is extremely powerful and if you have problems along the kinetic chain above and below the knee, this could cause you knee pain when going down stairs.

I've had some struggles with knee pain and found Mike Robertson's work on corrective exercise to be quite helpful. You can read some articles on his blog about the causes of knee pain here, and how to correct it here.