Warming up is necessary for all instruments, not only the shakuhachi. However,it often occurs in practice that you even if you warm up before a performance,there will be a long period of time after your warm up ends and before you can actually play.
You may have to wait on stage for others to play first, for instance, or for someone important to give a speech…When this happens, by the time you actually start playing, it’s as though you hadn’t warmed up at all.
If your shakuhachi gets cold, the pitch will rise as it warms up when you play.In order to avoid this, try keeping it warm with your hands on stage. Even if you do this, though, the “feeling” of being warmed up might not return right away when you play. However, the softer a person plays, the less likely not being able to warm up is to affect them.
To understand why, imagine what 100 meter sprinters do.They warm up extensively, stretching all their body parts, until right before the race, when they burst into action. If they don’t do this, they won’t run well at best, and at worst will injure themselves.
People who play powerfully, using all their energy and abilities like as printer, rely more on warm-up than those who don’t. However, if you can play with the muscles around their mouth more relaxed, then you will have to rely less on warming up.
Thus, it is good practice to start playing songs immediately without any warm-up whatsoever. You won’t be able to do this well unless you can play relaxed, so this will naturally help you learn to play in a relaxed manner.