External posture, or how one conducts the position of one's body when playing on the dizi, is important to support all the other aspects of playing. Note that here, we focus on the gross body positions as opposed to the way the fingers are laid out on the dizi.
We cover some general principles, followed by more specific ones for the two stances, namely sitting and standing.
A proper posture allows maximal control over tone produced by the dizi without injury or discomfort.
The basic requirement for external posture is to prioritise the neutral spine and positioning such that a natural range of motion is obtained. If at any point there is pain or numbness in any body part from playing the dizi, an improper posture is likely to be the cause.
The following are some guidelines for the head and upper limbs, and are applicable regardless of the stances used:
The head should always be facing forwards, even when looking at the score. It is not wise to nod or tilt the head in any position since that can obstruct the airstream, causing intonation issues as well as comfort problems.
As a corollary, the music stand should always be positioned such that if one were to look straight ahead, the conductor can be seen, and a slight lowering of the eyes are enough to view the music written on the score. Such a set up usually requires the stand to be at least two feet (or around 60cm) away from the dizi player.
The arms should be relaxed, with shoulders down and elbows at their ``natural'' position, i.e. without raising them beyond 45°. At the same time, the shoulders shouldn't be hunched forwards---a neutral spine position is much preferred. The wrists shouldn't be overly flexed (i.e. bent away from the palm)---they should be held as neutral or straight relative to the forearms as possible.
Sometimes, time may be counted through a careful movement of the upper limbs in concert---these must be coordinated with the head to ensure that the position of the dizi relative to the fingers and the embouchure do not change. Dramatic movements of any sort should be reduced to a minimum.
There are two main stances that one can play the dizi in, namely sitting and standing. We elaborate a little on the requirements for each below.
Much of dizi playing in orchestras involve sitting. Generally, sit such that the abdominal area is not unduly compressed by the thighs, with feet flat on the ground, i.e. do not cross the legs. With some chairs having a slight declination towards the buttocks, it may be necessary to use less of the chair's surface for sitting, i.e. the sitting bones of the dizi player will be closer to the front edge of the chair.
Since the body naturally twists to the left slightly when holding the dizi [in orthodox position], it may be necessary to counter-balance the position with the chair turned to face to the right so that the head (which is turned to the left) will face forward. This is definitely preferable than attempting to force the right arm to retract more just so that the body sitting in the chair can face the front squarely.
The standing posture is often used when one is soloing on the dizi or at times when one is practising on one's own. The chief advantage of the standing position compared to the sitting one is the near impossibility of compressing the abdominal area unduly.
Ideally, the feet should be in `L'-shape, with the left foot facing forwards while the right foot is perpendicular to it (also known as dingzixing (丁字形)). The feet shouldn't be too far apart---a good comfortable position of no more than shoulder width should be obtained. The weight should be distributed around 60% forward and 40% back, but this can be varied with no major issues.
Some light ``rocking'' movement (i.e. shifting the weight from leading foot and back) is permissible as a means of keeping time and/or expression, but more dramatic movements ought to be kept at a minimum to avoid major performance issues for the diaphragm.