JT’s suggestion above is spot on. I also like the disruption model of thinking which in this case would mean finding websites you like that are specifically NOT in the fitness industry. This way you’re not contained or restrained by fitness-type sites. It helps you think broadly, differently. The other way to apply disruption thinking is to identify brands you really love, and ask yourself how would they do it, eg:
If Google was offering strength & conditioning programmes, what would their site offer?
If Air New Zealand… if the All Blacks…
In terms of the nuances of the fitness industry, if you have a really clear brief, any good website designer/developer should be able to deliver. One thing we used to specify in our marketing briefs back in my marketing day was what we want our clients to think, feel, and do when they engage with our site/product.
Hope that helps in this first stage. Good luck!