Would enclosing keywords in the text of your article body with the H1 tag help improve search engine rankings?
I know that enclosing keyword with header tags is helpful in terms of SE rankings,. but headers tags are usually done in title not on body,. You can bold it instead of header tag,.
Using H1 would surely help. But use it wisely. Don't overdo it. And don't use it in places you should not (eg in the middle of a sentence). Bold it instead.
Header tags do help rankings when they contain your targeted search terms. You should use them as headers and sub-headers above the content of your page.
As mentioned previously, it does improve you ranking if you enclose keywords in header tags, but don't expect a dramatic improvement and don't put header tags in illogical places. I suggest you to read the article about Google search engine ranking factors by SEOmoz on this effect.