Your body is an amazing machine. In order to keep it running strong, you have to use it. Machines that don't get used, get dusty with little baby spiders that crawl into crevices & make nests (i.e. achy joints). If you aren't exercising because it hurts or because it's too hard, that's the bump you need to overcome to get better. When you want to quit and you don't, that's where improvement is made.
After I had my 2nd child, I spent a couple of years not moving and packing on the pounds. When I look back at that period of my life and compare it to where I am today, I feel 10 years younger now. During that stagnant period, my knees ached every day, my back hurt, and my attitude sucked. My attitude still sometimes sucks, but my joints feel great! I feel like they're stronger and lubricated and (knock on wood!) nothing hurts. Unless somebody cross checks me in hockey, then I hurt for a while. Anyway, it's all because my parts are being used on a daily basis. If you sit still, the dust will come. And it hurts!
I'm going to go find a picture of myself during my sedentary days and post it. And my bff is coming to the gym with me tomorrow to take new pics of me looking awesome because the current photo of me to the right looks like I have chicken neck, which I do, but that doesn't need to be discussed. Or shown. :-) So tomorrow I will post then & now pics to show you what you can do just by moving. And eating less crap.