Four kids would definitely have its stressful moments!
You have really figured out how to manage your stress.
Going to the gym, taking care of your body, having a few moments of adult conversation, all of these are ways to revitalize you from the rigors of mothering.
The other nifty benefit of prioritizing your "me-time" is that you are modeling how to take care of yourself. I think this lesson is very important for our children. Boys can begin to believe that they are too tough or strong to need to care for themselves. And girls can get so involved with caring for others that they forget to care for themselves. So not only are you being good to yourself, you are being good for your children as well.
Congratulations on finding a perfect stress reliever.