My legs feel fatigued when I walk up just 8 stairs or so, or if I walk uphill fast. I can bike for miles, but I can't do these other activities. I am 57 years old, and this has been going on since I was in my 20s. I feel as if it is getting a little worse. I can't jog anymore because of this sensation. It feels as if I have been sprinting, and my legs feel so uncomfortable that I have to stop and bend over. My breathing is fine. When my doctor asks me to push with my legs against her hand, everything is fine. I don't feel pain, just extreme fatigue.