Punching Bag/ heavy bag
I am gonna get in trouble for this, but here goes.
One of the reasons that closed fist techniques were introduced was to keep the power of the chi/ki from fully integrating with the strike, thus causeing serious injury or death ... or so I have been told by two or more masters who have practiced Chinese arts with pressure points and chi application strikes.
As for the health, mind and body training, reflexes, or just plain having the technical ability to properly punch, strike, kick, or poke the soft easy points of the human body ... the punching bag and the heavy bag are excellent tools for this purpose.
Part of learning to kick or punch is learning to strike through the opponent making them feel like some giant has applied the pain of contact!
Each of the strikes ... knuckle punch, leapard strike, closed fist punch, knife hand, and a variety of kicks are designated for angle and direction to particular situations at various pressure points on the human body. Examine the striking charts most Karate schools/ or martial arts stores have, and they show many of the easy points. They do not explain how to activate them with rub, strike, or push, nor do they give angle and direction? You won't find them in average books, but will find them in pressure point books or those kind of books for people who study them?
Of course, when your sensei gives you an opening in an Aikido technique, do you know what to do, or do you see the various openings available? Probably not, because that is another form of study best left out ... we don't need accidental injury in our Aikido training. Still, it is in your studys.
Observe the angle and direction we use normally in most Aikido techniques, and you have a piece of the puzzle. Take the time to learn Basic closed fist, and knife hand (Te gatana) and that is the basic striking and hitting needed for over ninety percent of Aikido strikes ... should you ever need to strike.
The secret of striking through, or being able to use your entire body to move an object, without ripping your knuckles into a bloody mess will be the center of your practicing on the moving punching bag, or stationary heavy bag. When you hit the heavy bag so it bends in half or kick it so it changes its hang to a horizontal position, I would say your full power is in effect and you have a handle on letting loose the power you keep restrained at practice? Let it out, smack the stuffing out of them bags! If the heavy bag ain't duck-taped you ain't practicing hard enough!
There are many types of fighting, some involve boxing, constant lightfooted movement ... which is great for cardio-vascular system. Once you learn to use the angle, direction of all types of punches and kicks on the heavy bag ... doing them to a person almost becomes childs play? You might find that it is nearly impossible for someone to escape your Aikido techniques once your reflexes have been honed with speed bag ( striking bag suspended between rope and shock cord that allows for quick movement).
Don't expect your Aikido teachers to teach you all the different ways to kick and punch, most Japanese have had some type of martial training in another open hand art that covers kicking and punching when they come to Aikido. They have basically ... learned the basics, it makes Aikido so much more fun!
Besides, it couldn't hurt to know what kind of weapons you could be facing from an attacker and have them in YOUR back pocket for a rainy day?