The science behind a punch?

What muscle groups are involved in punching. I have tried punching stuff myself mostly a heavy bag and I feel it mostly in the shoulder area. I think the reason behind this is because I learned off of YouTube a technique called the "Shoulder-Snap" which utilizes your shoulder movement mostly which is how you are meant to throw your punches properly.

There are four main punching techniques and they are the jab, hook, uppercut and cross. I am wondering what muscle groups are involved when throwing these punches also how can you effectively increase punching power, I read different articles teaching about different weight exercises to boost punching power as well as implementing different types of techniques in order to also increase punching power but I tested these out myself and found that I felt more stiff when throwing punches, I don't know if what I feel equates to whether or not I am effectively increasing my punching power. I tried also hitting the heavybag about 3-5 times a week and felt like I got the best results, which I don't know why. But I am wondering about you people with possibly in-depth knowledge on human anatomy can maybe help me with this.