Before I get started, let me just say that there are a lot of different theories out there on how to hit harder and what you should or shouldn't do. This article is going to tell you what I've found in my own training and experience. I don't expect everyone to agree with everything that I say. People train differently and have different types and levels of knowledge and experience. I'm just going to share with you a few things which I think are important to punching power and that have helped me personally over the years.
I don't mean going and bench pressing 300 pounds or doing latt pull downs on weight machines an hour a day or anything like that. What I've found is best for building up muscle for any physical endeavor is to come as close to that action as possible when you are working out. So, what I like to do is get two evenly weighted dumbells and their weight will depend on your physical conditioning. Don't try to do too much too fast even if you are used to lifting weights a lot. Just because you can do bicep curls with forty pound dumbells in each hand doesn't mean you want that kind of weight to start out with this. Trust me. If you use too much, you may hyper extend a joint, pull a muscle, or even drop the weight on your foot or something of that nature. Start light. Work your way up. What you're going to do is just stand there and do dumbell punches. You see them doing this stuff all the time in aerobics and the like. The difference here is that you're not trying to work your cardio right now. You don't really need to raise your heart rate all that much. What you want to do is slowly throw your punches out, making sure to move your hips and bend your knees with the punches as is appropriate. When one arm is holding a dumbell out in a punching fashion, the other arm should be back against the body, holding the weight up as if having your guard up with your free hand. Also, remember to breathe out as you extend your arms outward with the dumbells and in as you come back. This may seem simple, but it is amazing the difference you'll see after you do about twenty or so punches like this and then put the weights down and throw a few punches.
2. Knuckle push ups
This one is more to help condition your knuckles usually, but it has another benefit. It helps you to keep a tight fist. If your fist isn't tight while doing knuckle push ups, you aren't going to have a very enjoyable work out. And likewise if your fists aren't tight when you're punching, you won't get maximum power out of your strikes and you may damage your hands. Now, I should point out that I'm talking about a good closed fist when you get to your target. A lot of people close their fists too soon. If you start out with closed fists, you start out with muscles that are more tensed than if you hand your hands open. Tensed muscles cannot move as quickly. This means they are less likely to land on the target without being blocked or avoided completely and it gives them less momentum to help with the build up of power.
When I say form, I don't necessarily mean any specific art and certainly not kata. I mean using correct pysical form or body alignment. If you are not properly aligned, you can be knocked of balance more easily and your punches will not have the right direction and flow of force in them that they could and should have. One of my teachers used to have me throw punches in the air at full speed and force. Then, he would randomly yell for me to stop and I was supposed to just freeze in whatever position and phase of the punching I was in at that moment. He would then come over to me and start pushing, nudging, and some times lightly striking different areas on me to test my balance and power. This is a good thing to do if you have a partner you can train with. If not, try shadow boxing in a mirror and try to see if you think you're aligned the way you should be. If you're honest with yourself, you should be able to figure it out pretty easily.
4. Follow through
This is a big one to me. I have a friend who has given me a seemingly endless amount of grief over the years when we've worked out together and I've tried to show him a new punch defense. The reason is that as I would have him simulate an attack, he wouldn't actually throw his punches in a manner that would ever actually hit me. He would pull back too soon or not put any of his weight into the punch. Then, he would tell me my defense wouldn't work. And I would always point out to him that if someone were trying to hit me, unless they were using a feint, they wouldn't pull back before actually making contact and if they hit me with as little behind their punches as he had behind his, I wouldn't need a defense, because they would never hurt me. It's important to train with the concept of follow through. If you really want to hit hard, you can't hit at your target. You have to hit through it. Don't aim for your opponent. Aim for about three inches behind him. That's why it's so important to train at least some on a heavy bag. You can hit as hard as you want and you don't have to worry about hurting your training partner. That being said, some people will say that if you're going to put that much into a punch, you're putting yourself out there a lot and if you miss, you're screwed. Well, that's why it's important to build your punching speed as well. And of course, you need more than just punching to be a good martial artist or to really be good at defending yourself. You also need to know when to punch, kick, grab, etc. That takes a lot of training which I won't cover here. But when you do punch, you want it to count. So, I hope these few pointers are helpful to you. They've always served me well.