Turbo-Charge your Striking Power
The legs are integral to the development of striking power.
As force is increased through the foot's contact with the ground, it moves up the leg as a wave and joins with the force generated through the rotation of the hips. This rotation allow for greater extension and projection of the accumulated force. Simultaneously the abdominal "core" is contracted and pressurized so that the force has a stable "platform" to project forward from as the fist (or palm, foot, etc) impacts its target. Some martial art systems teach use of the kiai at this point, to increase the pressurization in the abdominal cavity. Keep in mind that the hip joint is complex and involves a large mass of musculature. Some martial art systems emphasize training the muscles of the inner hip (piriformis, iliopsoas, etc.--baguazhang is famous for this) rather than simply the large muscles of the outer hip, such as the gluteals.
The hips are integral to the development of striking power.
"Now", you say, "I got it". But wait, there's still one key mechanical component to add, if you want to maximize your punching power. The expansion and contraction of the muscles of the thorax will generate incredible power when applied to a strike. The reason is because we are talking about very strong muscles, the muscles that are involved with respiration such as the intercostales and subcostales, and the diaphragm. The latissimus dorsi (lats) also act as an accessory muscle in respiration. As the legs are propelling the force forward and the hips are rotating and extending the force, the torso will be forcefully contracted as the strike impacts its target. One should note a strong compression in the abdominal region and the ribcage.
The muscles of the thorax are integral to the development of striking power.
The exercise that I have found to be very useful for teaching the body how to properly contract the thorax is the Russian Military Press. If you are not thoroughly familiar with this exercise, review the RKC video and book and practice the RMP with kettlebells! With some practice, you will get a very clear sense of fully expanding and fully contracting the muscles of the ribcage.
Once you have developed the full range of motion with the RMP, put down the KB and practice the same movement with just your body. You should still be able to create the proper tension throughout the body. With the hand that is not pressing, place your fingers over the side of your ribs on the working side. As you press the hand overhead, you should feel the ribs on the pressing side open fully, so that you can poke your fingertips between the ribs. As you pull the hand down, feel the ribs closing around your fingers, so that at the bottom of the compression, your ribs form one solid 'vest', and your fingers cannot penetrate between the ribs. It is very important that you fully compress at the bottom of the movement. Think of corkscrewing the elbow down into the body as you pull the arm down. Feel a solid linkage from the armpit all the way down to the hip, so that the lats and obliques feel like one continuous muscle.
Over time, you will learn to easily expand and contract the muscles of the thorax and will be able to do so with less and less movement of the arm. Progress to the point that you can solicit the full expansion and contraction of the ribs without having to move the arms at all. Once you are at this stage in your practice, you will be able to transfer this muscle control skill into your strikes.
The legs, hips and torso and involved in all types of strikes, be it straight punches, uppercuts, hammer fist, elbows, knees, or kicks, as well as in grappling and throwing.
To incorporate full body power into a strike, there must be power generation from the legs, hips, and torso.
There is more, of course, to generating powerful strikes than the basic mechanics discussed above. Other key components include technique, timing, and balance, as well as strengthening weak links in the body such as the wrist for punching and the foot/ankle for kicking. However, by learning how to properly integrate the strength of the torso with that of the legs and hips, you are enhancing your ability to maximize your striking power.