ADHD and sticking to a plan???

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I'm wondering how others with ADHD manage to stick to a menu, exercise plan, or frankly manage to continuously fight the impulse eating and exercise distractions? I'm trying to find more active hobbies since my current favs are reading, crafting, and computer gaming. But I also have asthma and a bad back so it's difficult to find something that doesn't aggravate those. I'm looking into yoga or tai chi as a start, but so far have managed to get completely distracted each time I've begun researching, or any time I pop in a DVD. I'm considering a class where I actaully have to show up... has that worked for anyone? I work full time & am taking classes, so I've been having trouble finding a class I can work into my schedule. Any ideas? Thanks all!