I'm thinking someone being healthy has alot of energy and strength and brain power so with this I suggest thepowervault.com or thepowerzine.com hopefully this will spark some creativity.
If not mind about the hyphen, the two following domains are not registered at this moment. fit-boot .com fit-after .com (For your reference only.)
You can grab a good domain name yourself, you need to be a little creative and you should give time in research..
My suggestion, professionally never ask! A better question would be, what are key elements to keep an eye out for choosing a domain name! And here are some tips, some are very obvious! short international? then go for the obvious international extensions local? go for a local domain name (SEO) Make it personal, be proud about your name. Don't always use the most obvious names like in your case Fitness (but will help SEO when choosing words that you want to rank high) Don't be scared of hyphens. There is nothing wrong with it. Be original. Ultimately if your lazy and need help. Well with a little enthusiasm use http://www.randomainer.com/ (you never know what shoots out that might inspire you) These are just a couple of things to look out for.
If you don't have a name in mind, then let someone else decide for you. Go to places that have expired domain names. Do a search for ones that are .com and have health in them. You can usually buy those cheap, and just check that they don't have some bad history with a Google search. The benefit is that you can pick up domains that are 'aged' and maybe also have backlinks, and even pagerank. I picked up a PR4 two-word travel .com domain this way for $10. Hope you like this idea.
Type the domain name into Google. If you find spammy stuff / porn etc - then you are warned off. If however you find NOTHING - that is even worse, because it may mean that Google has blocked it from showing up, and you should then avoid it too. Anything else is probably fine.