All types of martial arts are full contact sports that test your endurance and pain threshold. In order to dish it out and defeat an opponent during a fight you have to be able to take a few hits, punches and chokes without going into shock. The best way to ensure a high level of performance and effectiveness during a martial arts bout is to prepare your body and mind during training through conditioning and desensitizing exercises. That does not mean you should let anyone beat you into oblivion, but rather try to gradually adjust to a higher pain threshold.
The mixed martial arts fighter, Caroline Portugal, says:"My body is adjusting very well to the conditioning and desensitizing training. All athletes must heal and rest. When you are doing high impact training by taking hits deliberately it adds a lot of stress to your body. Therefor, it is important to help your body recover and eventually adjust by giving it time to heal."
Portugal goes through sequences of taking kicks and punches to different parts of her body while flexing her muscles to protect her soft tissue and bones from any impact-related damages. These hits subsequently lead to bruises. With continued training, however, the body adjusts and bruising decreases while the pain threshold increases.
Using protective gear like shin guards during martial arts training may prevent injuries. Nevertheless, it does very little in preparing you for a competitive bout unless you are allowed to wear protective gear at the official tournament. You should try to replicate the tournament conditions during training as much you can.