Make exercise filtering (tags) more flexible and personalized to the trainer's worldview. It should be possible for trainers to classify exercises according to their coaching methodology. That will make it that much easier to create workouts quickly and with ease for customers.
Examples:
I'd like a tag for leg exercises in general (not only glutes or quads), i'd also like to be able to tag exercises by context, is it ideal for home, gym or park workouts.