I'm doing the c25k too, but instead of increasing the speed I am increasing the incline on my treadmill. hopefully by the end I'll feel steong enough to speed up. maybe that will work for you too?

I think its different based on each person. I know for me its not until I'm in the lower 200s that I can start running because I get shin splints easily and have weak knees and ankles. Other people weigh more and can run no problem.

My suggestion if you feel that you can start running, start slow and easy, listen to your body and go from there.

I am also doing the C25K. Currently I am close to 320 (give or take) and I try to run for about 10 minutes per day and walk an additional 20.

Doing C25K is great - but if you're in the 300s you have to also strengthen the muscle that supports the knees, abs, and back. Idealy, start strengthening these first, then start running so you don't hurt yourself. I started running when I was around 315-320 a little over a year ago. But I started strength training first because I felt pain in weird places when I ran.

Start with adding squats to your routine every day. 2 sets of 10 if you can, but if you can't, try 2 sets of 5. Use a ball beween your back and the wall for stability and to make sure you maintain proper posture. Work up to more, but it might take a while.

From squats, I added a whole bunch of weight machines and other body weight exercises that centered on strengthening the core. Back - abs - butt and the muscles that support the knees (squats and lunges were amazing for me).

After about a month of concentrating on my core, I started running and all the weird pain was gone.

Go very slow. Pull that speed down to where you are just pushing a running type form, but don't go fast. I think my first speed was like 3.8. I have very short legs though, so this felt like flying. I run at 4.5 now, but it took a while to comfortably build up to that.

Spend as many weeks as you need for each C25K week, and don't sweat it. I think I spent 4 weeks on Week 1, Week 2, and Week 3 each before running became easier. Run with your treadmill set to an incline of 1 - this will simulate running outside more accurately and will take some pressure off your ankles.

On days you don't run, try incline intervals on the treadmill while walking.

The first time I tried C25K, I did so on the treadmill and got up to week 8 and 28minutes of jogging (slloooowwwwllllllyyyy) but I had to stop b/c of hip pain. I was 355 at the time.

Now I'm 325 and I'm starting again. I'm only on W2D1 but so far so good.

I think Supergirl6 gave you the absolute best advice. Work on strengthening the supporting muscles. That's definitely what I'm going to do.

I'm 320 and only 5'4'' so I have to be kinda careful running. I usually run barefoot on a treadmill or use minimalist running shoes outside. I avoid heal-striking at all cost and focus on a midfoot strike so that my calves act as shock absorbers and there is minimal stress on my joints. I was running 3 miles daily without any problem, but then I had to go on bedrest for several months because of my dysfunctional pregnancy. Now I'm back at square one with my running, trying to work back up from being completely out of shape. My doctor is more supportive than most. She thinks it's great that I run. I'm sure there are many docs who would look at my body and suggest I just walk. As a fat runner I think I have to be more attentive to any discomfort and really listen to my body to know when I can push and when I need to take it easier. Best of luck to you! Running rocks!