Trying to get back into shape

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Hi everyone. I am 30 years old and a few months ago I was in the worst shape of my life. I've been doing better lately, and I hope this will help me. About 6 years ago I was down to 187 pounds, as of this morning I'm at 256, which is a few less than a month ago. I have knee problems and bad back injury so it is hard for me to find a workout routine that is relatively painless (any advice would be appreciated). Anyways I'm looking forward to taking the next step in getting fit.