Metrics that you are analyzing are percentage, It means if integers values decreased probably percentages will increase. So, you need to understand what are website long-terms top ranking. If you provided information contents without a call-to-action or your blog user experience is no good, probably your blog wil keep a low performance.

Best choice is create a subdomain, because each trainer Will have a different content and layout. But for Google each subdomain is a new website, no share relevance between them. If you can use a page model for each trainer, you can use directory structure such as domain.com/trainers/name, so you will distribue link juice across pages, improving website architecture.