Fitness Instructor Training

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I've been playing with the idea of becoming a kickboxing or a yoga instructor for a few years now. I know they've been hoping to find a reliable KB instructor at work for classes at lunchtime. Mainly in just looking for some feedback from those of you who are currently teaching group exercise classes. What is the certification process like? What do you enjoy about teaching, and what do you find frustrating? I'd like to get an idea of whether or not it's for me.