You haven't made it clear what the purpose of your practice is. "Ma bu" or "Ma bu" exercises the endurance of thigh muscles. It is certainly beneficial, but you should do what you can and don't stay too long, or you will strain your knee. Self-defense has nothing to do with "Ma Bu Ping". Learn special self-defense, how to attack people's key points, how to subdue people with joint skills and so on. Don't be too obsessed with specific actions, it's not a martial arts secret. Practice at will. If you are tired, it will definitely have an exercise effect.