Hi Roy. Though most trainers on this site and elsewhere probably use a client agreement or contract, I would strongly caution and advise you that it’s BEST to seek the advice of an experience small business attorney (preferably one with experience working with a fitness professional). This will give you the opportunity to sit down and discuss your specific needs and business operation, so that a Client Agreement that directly addresses your needs can be drafted.
Yes, there are certain provisions that ‘may be’ typical to most if not all such agreements, but in my opinion, there is no real boilerplate language that covers everyone’s situation — we, and our training practices are all different.
I hope that this helps.