You can't help but engage in the kinds of changes Jess and I have and not learn a few things about your own body. And one of the things we've discovered is how truly incredible the human body is. We have learned to communicate (in a way) with our bodies to tell it what we need from it and it will communicate what it needs from you.
Your body requires fuel to keep all of it's processes running. Everything from voluntary motor functions like walking, speaking, running, cycling etc.. to the smallest involuntary functions like cellular division and hormone production requires energy from the food we take in. How your body spends the energy you consume, though, is subject to input from ourselves. If you work at a job that requires you to sit in front of a computer screen all day and you go home and sit in front of the television at night you are sending signals to your body that these are the normal functions that must be fueled and so your body will reallocate energy that would be used for building muscle, bone density and cardiovascular health to other areas of the body such as to nervous system functions and the immune system. Eventually, these systems get so much energy that they become over active and cause a wide array of health problems.
Now on to the good news...if you begin telling your body than in addition to the hours of sitting it must be ready to tackle it must also devote energy to build up your endurance and support systems to take in a 30 min walk once a day, your body will begin funneling that excess energy to building up the parts that contribute to making it possible to complete those walks. Furthermore, if you tell your body that instead of walking 30 minutes a day that you will be running for 10 minutes and walking for 30 it will devote energy to ensuring you can carry out these activities at a proficient level.
Here's the thing folks, we all have different starting points when it comes to taking on a lifestyle change. Get started doing something each day that pushes your body toward your threshold for effort and over time your body will respond in a very positive way. Forget people telling you that (fill in the blank) exercise is bad for your knees, joints, heart, head, feet or whatever. Anyone that tells you that exercise can be detrimental to any part of your body is making excuses for their own lethargy.
Trust your body and Happy Running!!!