This is a huge mistake. You should not try to implement a ‘template’ becuase there are too many variables involved for one idea to be successful in a completely different circumstance. For example, Some Best Buy stores do well and others have been closed down. They all used the same ‘template’.
You have to gather the demographical components of your particular situation and design a business model that can take advantage of your particular environmental conditions and parameters.
I am sure that you are aware of companies that assist with business plans. Here is one example: http://www.masterplans.com/business-plan-articles/fitness-studio-busines….
I would consider a good template helpful because it will take you through questions you may not have thought of. While it is true that every situation is unique, collectively there are only so many ways of running a fitness business.
I wish you good luck.
I have been writing business plan as well for my business, and a good source fo it was http://businessplantemplate.club/. Also you need to think about a lot about details of your business before creating business plan.