Martial Arts Based Fitness Classes Are, Probably, Not Doing You Any Self-Defense Favors
Martial arts have been used for exercise for a very long time. You should know that there is a big difference between fitness and fighting though. A lot of people get those things mixed up. However, you have to consider who is teaching the concepts. A lot of those people are just fitness professionals, which is fine, if you are looking for fitness. Yet, you might find that a lot of the techniques you train in class may not be optimal for actually fighting someone when something is on the line.
What is the problem? A lot of the punches are shortened, the kicks are not as powerful, and your bones are not ready for it. The truth is that hitting things actually counts. Why? Your bones adjust to contact. They grow stronger because they know that this is an activity that they do often. (See https://livehealthy.chron.com/punching-bag-make-knuckles-bigger-3035.html). Of course, the thought of hitting things is intimidating. Especially if you were taught to be meek. There is no shame in that because I grew up, not necessarily taught from my father, that I should be meek and listen to my elders.
Hitting things feels like crossing a line at times. It can really start feeling like something else if you take the proper mechanics to heart. It is addicting, because the sound of the “boom” when contact is made, can be amazing if you were never taught you can generate power. That being said, getting to that point may take some time to get there. At least, to get the mental headspace to allow yourself to hit something hard and know you are not going to lose control.
Building up is a good thing. Using the other fitness classes to build up to it is fine. You just need to know what you are doing and how limited techniques you have in a real fight. If anything, you might develop the cardio to defend yourself for a very long time.