I am beginner at aikido and when I train, for some reason I tend to hold my breath when I should be exhaling. Mostly during falls and techniques where I'm nage.
Is there a way to get rid of this bad habit, other than eventually it will happen on its own?
This is a fairly common problem on both sides of the equation. We have to continually emphasize the importance of breathing during the techniques with newer students… and the importance of breathing out when having a technique performed on you. So step 1 is to trust that everyone in the room you are practicing has probably had this problem before, either in this or in another art.
As to things that you can do to improve:
When a technique is being performed it is very easy to get "caught up" in either the motion or, more frequently, in some specific part of the motion (e.g., in a strike-then-lock pattern it isn't uncommon to see people get preoccupied with the coming lock and thus throw a halfhearted strike). The goal here is to work to stay present all the way through the technique.
Essentially when doing the technique take it slowly (where you can) and focus on the flow and on how to breathe through the technique. When observing a technique make a note not just of how the bodies move, but also of how the participants breathe.
Take 10 minutes a day and do a breath awareness meditation of some sort. This doesn't have to be super formal (I used to do it on a train), but basically just pay attention to your own breath for ten minutes. Breath by Breath is a good basic guide if you are interested in the Buddhist variation of this practice.
Pick up something in addition to Aikido that makes syncing breath and movement explicit, e.g., yoga (or, heck, even running). Essentially find a practice where breathing is not optional and proper breathing is emphasized. Your branch of Aikido or your instructors may even have such a practice built-in which you can do on your own (hapkido has danjeon breathing).
Start paying attention to your breath more in your everyday life. You'll find yourself holding your breath in very small fashions - when you wait for a thought to begin, or complete. When you're watching someone's movement and you're not sure.
When you're typing at the keyboard. All those micro-moments when you're holding your breath. Start working on releasing those, and let your breath flow freely. This will help you realize what is happening in the aikido class and fix the problem.
I think I've been doing aikido for 12 or 15 years now. I'm still waiting for that habit to go away on its own. I still catch myself holding my breath.
Things that work for me:
Kiai - (Not all the time, but there are techniques where it helps. On the other hand, you get some funny looks) (I'm mostly not serious about this one)
Hiss - Particularly when doing breakfalls, I try to be very aware of breathing out. I purse my lips and kind of puff or hiss the breath out to make sure that it is going smoothly. (Holding your breath during breakfalls is somewhat self correcting; the pain will remind you that you've just done something dumb. )
Weapons Work - I've found that it is far easier to work on my breath control while doing weapons work. Inhale when I lift the sword, exhale when I lower the sword. Inhale as I position the jo, exhale when I strike.
I've seen some other aikido players utter a very soft, almost subvocalized "Hsssu" at the point where they would apply atemi (that depends on your school/lineage).
Beyond that point the answer gets much more detailed, and depends in part on which type of aikido you practice.
Something that may help: take a short kata, something that you can do yourself is best if not find someone who does not mind doing the same thing. Personally, I use either the 6 or 18 count jo kata. Do the kata for one minute non stop. Then rest for a minute. Do the kata for two minutes non stop, rest for one. Do the kata for three minutes non stop, rest for one. Keep doing it so you can do the kata at a good speed for 15 minutes. You will either learn to control your breathing or you will die. The trick is to breath normally and neither force it nor fall into a breathing pattern. It will build your endurance as well.
