Hello Dr. Simpson,
I have done promotions in the Fitness/ Health niche and my experience has been it is much more difficult to create partnerships in this niche in comparison to the IM niche.
I have used a similar approach...i.e. offering help, promoting offers etc however it has produced limited results in forming solid JV partnerships.
The push in the fitness niche seems to be (my opinion only) a partner would promote for you if you were a student in their mastermind group etc. where they can use your results to promote their success.
This is not a bad strategy, it simply can be cost prohibitive.