I view martial arts as the best workout you can get. Sparring in any combat sport works the entire body. If you grapple or strike, you're using every muscle in your body and you have the resistance of another human being, making this type of training the most functional and effective resistance work you can get. The drilling, stretching, bag work, etc. in addition to the sparring will give you well rounded workout. So, practice your art or sport to it's fullest. Learn to make it work for you.