Interesting story in Information Today...
Cognition launches Semantic Medline
"...enables complex health and life science material to be rapidly and efficiently discovered with greater precision and completeness using natural language processing (NLP) technology"
I tried a quick search "exercise and depression" just to see it working - results are mostly relevant on the first couple of pages - it does offer you to select the correct meaning e.g. of depression (feeling of sadness/hopelessness) but still seems to bring up records referring to other meanings (e.g. ST segmental depression) - although I guess it's impossible to avoid that - and the definitions might be more useful if sourced from a medical dictionary which they don't appear to be. It would be interesting to compare results using MeSH.
Given that my search retrieved over 7000 results, it would also be useful to have some options for narrowing the search - suggesting additional search terms (e.g. are you interested in a particular population e.g. postnatal?)