The arms
The image has four arms, two normal ones in front, two additional ones closely behind but attached to the frontal ones, which seem to sprout from the shoulder joints. The front arms are both turned rightwards; the left one is so stretched to the right as to cover the bosom, and is known technically as Gaja-hasta ("the Elephant-Hand") or Daṇḍa-hasta ("the Staff Hand"). It is bent at the end, with the fingers pointing towards the bent left foot (called Kuñcita-pāda), in a graceful manner.
The Daṇḍa-hasta is indeed indicative of a position conducive to the practice of breath control (prāṇāyāma), which is essential to yoga. As a consequence of the particular position of the legs, the apāna ("the Downward Breath", approximately) has moved upwards, and needs now to be held in check lest it relapse downwards. And this is achieved by the stretched left hand, which is actually pressed somewhat upon the bosom, upon the left portion, the prakṛti-bhāga, of the frame. The band that is tied at the waist - at the point of the diaphragm, reinforces and reiterates this pressure. All this is a matter of sheer yogic practice, hardly recorded in yogic texts, and there can hardly be anything to "prove" here with a mass of textual evidence, except the actual yogic experience of a master-yogin, endowed at once with expertise in observation and articulation that Śrīraṅgamahāguru was.
Prāṇa and Apāna
The front right arm is positioned in the gesture of "Promise of freedom from fear" (Abhaya-mudrā). As for the hind arms, they are stretched sideways. The left arm is bent at the elbow accentuating its beauty. This ardha-candra ("Half-Moon") hand holds a blazing fire. The right arm in the rear holds a hand-drum (ḍamaru), which Śiva appears to be sounding gently. The fire and the drum respectively represent prāṇa and apāna (the twin aspects, the upward and the downward flow, of "vital energy"), there being a general equation between apāna and agni ("fire"). In fact, the ḍamaru itself symbolises the "movements" of prāṇa and apāna, for the alternation of the two strings of this drum expresses the movement of the jīva.
It is this balance or harmony between prāṇa and apāna is what is considered the very essence of prāṇāyāma (Cf. Bhagavad-gītā 5.27 : prāṇāpānau samau kṛtvā).