Im 15, been doing shotokan karate for the past 5 years. I earned my black belt last month, and it wasn't easy on any level. However, after 5 years of doing shotokan, i want to take another style of martial arts. I don't want it to be anything fancy, i want it to be a tough martial arts style that trains your internal muscles and gives you strength and the upper hand in street fighting; a practical style of martial arts i guess. Any suggestions of styles that would fit this description? thanks in advance