your content needs to be around keywords that...
1) have search volume
2) are easy to rank
Regarding #1 I can tell you from experience (I've done this 12-13 years ago when I've been newbie at SEO) that if you write articles on random topics, without checking if those topics are typed into google by people you're gonna end up with a huge pile of content that nobody reads. So, fire up your favorite keyword research tool, put some seed keywords in it, and let it find you some (50-100) long tail keywords that get search volume. Even if they only get 10 searches per month, it's still better (because you can rank for them faster than keywords with 2000+ monthly searches that could take you years) because...
The fitness niche is competitive, especially when you're a newbie and don't know how to approach it. This niche requires a lot of content and a decent domain authority to get on google's 1st page (where all of the traffic is), and if you don't know how to build up your domain's authority (the thing called DR that SEOs use to assess a domain's... well... authority
) you're gonna have a hard time ranking even for keywords that are deemed "easy" by your favorite keyword tool.
Actually, if I think better, it might be better for you to find even keywords without search volume (which are very long tails, usually, like 10-15 words long... or even question type keywords, these are also easy to rank for with the right approach). And the reason you might want to start with keywords that have no search volume is because most people don't bother with these keywords since... well... they get no traffic (although, this is not always true), and so the competition is lower for these keywords.
Like I said, find 50-100 of such long tail keywords and / or questions that are not addressed very well in google, write 50-100 words around each question (if you go the questions route), or 800-1000 words around the long tails (if there is enough info to write about, otherwise you can keep it to 500-600 words, no problem), publish those and - more importantly, and probably the hardest part - get them indexed in google and start building links to your domain's homepage to increase its authority while those 50-100 articles age and - hopefully - get some traffic after the sandbox period which, given the niche, it's more than likely to happen and can last anywhere from 3-4 months to 1 year or more.
Here's a guide to help you find good keywords to rank for:
https://ahrefs.com/academy/seo-training-course/lesson-0-1
And here's a guide to help you create content that ranks:
https://www.blackhatworld.com/seo/guide-full-example-of-how-to-do-on-page-seo.1251425/
definitely! That's the best option for you as a newbie, and in a tough niche like fitness. The good news, however, is that fitness can also branch out in a ton of sub-niches, and if you do your keyword research right you're bound to find some good keywords
