Domain advantage will not be passed on to the subdomain. Google will treat the subdomain as a different website.
If you want to pass site juice to the trainer pages, then set it up as normal pages, like:
domainname.com/trainername
domainname.com/trainername

Buying new sites for all trainers will not pass domain juice. I hope this helps. In case of further help with SEO, email me at varun@upreports.com