I would go for Workout Instructor (domains are available expect .com). Using a dash they are all available. It seems that your service is quite rigid and spammy, and instructor is the word that comes to my mind when I think of those adjectives.

http://www.123-reg.co.uk/order?domain=www.workoutinstructor&... http://www.123-reg.co.uk/order?domain=www.workout-instructor...