Handbook of Liturgical Practice of the Russian Church Abroad
A custom has emerged in some places, which is in fact an adoption of heterodox customs, of clergy and servers in the Altar ‘half bowing’, or inclining their heads or upper bodies forwards, at various moments in the Divine Liturgy (e.g. the ‘words of institution’, the epiclesis, and so on). This is not a practice of our Church and must not be done.
In the Altar, we always stand fully upright and attentive; and at the appointed solemn moments we cross ourselves and make either a bow or prostration (as prescribed). Other postures of what amount to expressions of personal piety are not appropriate within the Altar, or elsewhere in the temple.